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Title: The Student's Elements of Geology

Author: Sir Charles Lyell

Release date: February 1, 2003 [eBook #3772]
Most recently updated: February 22, 2021

Language: English

Other information and formats: www.gutenberg.org/ebooks/3772

Credits: Sue Asscher

*** START OF THE PROJECT GUTENBERG EBOOK THE
STUDENT'S ELEMENTS OF GEOLOGY ***

T h e S t u d e n t ’s E l e m e n t s o f
Geology

By SIR CHARLES LYELL, BART., F.R.S.

AUTHOR OF
“THE PRINCIPLES OF GEOLOGY,” “THE ANTIQUITY OF
MAN,” ETC.

WITH MORE THAN 600 ILLUSTRATIONS ON WOOD.
NEW YORK
HARPER & BROTHERS, PUBLISHERS
1878

CONTENTS.

PREFACE
Chapter I—ON THE DIFFERENT CLASSES OF ROCKS.
Geology defined. — Successive Formation of the Earth’s Crust. —
Classification of Rocks according to their Origin and Age. — Aqueous
Rocks. — Their Stratification and imbedded Fossils. — Volcanic Rocks,
with and without Cones and Craters. — Plutonic Rocks, and their Relation
to the Volcanic. — Metamorphic Rocks, and their probable Origin. — The
term Primitive, why erroneously applied to the Crystalline Formations. —
Leading Division of the Work.
Chapter II—AQUEOUS ROCKS—THEIR COMPOSITION AND
FORMS OF STRATIFICATION.
Mineral Composition of Strata. — Siliceous Rocks. — Argillaceous. —
Calcareous. — Gypsum. — Forms of Stratification. — Original
Horizontality. — Thinning out. — Diagonal Arrangement. — Ripple-mark.
Chapter III—ARRANGEMENT OF FOSSILS IN STRATA—FRESH-
WATER AND MARINE.
Successive Deposition indicated by Fossils. — Limestones formed of
Corals and Shells. — Proofs of gradual Increase of Strata derived from
Fossils. — Serpula attached to Spatangus. — Wood bored by Teredina. —
Tripoli formed of Infusoria. — Chalk derived principally from Organic
Bodies. — Distinction of Fresh-water from Marine Formations. — Genera
of Fresh-water and Land Shells. — Rules for recognising Marine Testacea.
— Gyrogonite and Chara. — Fresh-water Fishes. — Alternation of Marine
and Fresh-water Deposits. — Lym-Fiord.
Chapter IV—CONSOLIDATION OF STRATA AND PETRIFACTION
OF FOSSILS.
Chemical and Mechanical Deposits. — Cementing together of Particles. —
Hardening by Exposure to Air. — Concretionary Nodules. — Consolidating
Effects of Pressure. — Mineralization of Organic Remains. — Impressions

and Casts: how formed. — Fossil Wood. — Goppert’s Experiments. —
Precipitation of Stony Matter most rapid where Putrefaction is going on. —
Sources of Lime and Silex in Solution.
Chapter V—ELEVATION OF STRATA ABOVE THE SEA.—
HORIZONTAL AND INCLINED STRATIFICATION.
Why the Position of Marine Strata, above the Level of the Sea, should be
referred to the rising up of the Land, not to the going down of the Sea. —
Strata of Deep-sea and Shallow-water Origin alternate. — Also Marine and
Fresh-water Beds and old Land Surfaces. — Vertical, inclined, and folded
Strata. — Anticlinal and Synclinal Curves. — Theories to explain Lateral
Movements. — Creeps in Coal-mines. — Dip and Strike. — Structure of
the Jura. — Various Forms of Outcrop. — Synclinal Strata forming Ridges.
— Connection of Fracture and Flexure of Rocks. — Inverted Strata. —
Faults described. — Superficial Signs of the same obliterated by
Denudation. — Great Faults the Result of repeated Movements. —
Arrangement and Direction of parallel Folds of Strata. —
Unconformability. — Overlapping Strata.
Chapter VI—DENUDATION.
Denudation defined. — Its Amount more than equal to the entire Mass of
Stratified Deposits in the Earth’s Crust. — subaërial Denudation. — Action
of the Wind. — Action of Running Water. — Alluvium defined. —
Different Ages of Alluvium. — Denuding Power of Rivers affected by Rise
or Fall of Land. — Littoral Denudation. — Inland Sea-Cliffs. —
Escarpments. — Submarine Denudation. — Dogger-bank. —
Newfoundland Bank. — Denuding Power of the Ocean during Emergence
of Land.
Chapter VII—JOINT ACTION OF DENUDATION, UPHEAVAL, AND
SUBSIDENCE IN REMODELLING THE EARTH’S CRUST.
How we obtain an Insight at the Surface, of the Arrangement of Rocks at
great Depths. — Why the Height of the successive Strata in a given Region
is so disproportionate to their Thickness. — Computation of the average
annual Amount of subaërial Denudation. — Antagonism of Volcanic Force
to the Levelling Power of running Water. — How far the Transfer of
Sediment from the Land to a neighbouring Sea-bottom may affect
Subterranean Movements. — Permanence of Continental and Oceanic
Areas.

Chapter VIII—CHRONOLOGICAL CLASSIFICATION OF ROCKS.
Aqueous, Plutonic, volcanic, and metamorphic Rocks considered
chronologically. — Terms Primary, Secondary, and Tertiary; Palæozoic,
Mesozoic, and Cainozoic explained. — On the different Ages of the
aqueous Rocks. — Three principal Tests of relative Age: Superposition,
Mineral Character, and Fossils. — Change of Mineral Character and Fossils
in the same continuous Formation. — Proofs that distinct Species of
Animals and Plants have lived at successive Periods. — Distinct Provinces
of indigenous Species. — Great Extent of single Provinces. — Similar
Laws prevailed at successive Geological Periods. — Relative Importance of
mineral and palæontological Characters. — Test of Age by included
Fragments. — Frequent Absence of Strata of intervening Periods. —
Tabular Views of fossiliferous Strata.
Chapter IX—CLASSIFICATION OF TERTIARY FORMATIONS.
Order of Succession of Sedimentary Formations. — Frequent
Unconformability of Strata. — Imperfection of the Record. —
Defectiveness of the Monuments greater in Proportion to their Antiquity. —
Reasons for studying the newer Groups first. — Nomenclature of
Formations. — Detached Tertiary Formations scattered over Europe. —
Value of the Shell-bearing Mollusca in Classification. — Classification of
Tertiary Strata. — Eocene, Miocene, and Pliocene Terms explained.
Chapter X—RECENT AND POST-PLIOCENE PERIODS.
Recent and Post-pliocene Periods. — Terms defined. — Formations of the
Recent Period. — Modern littoral Deposits containing Works of Art near
Naples. — Danish Peat and Shell-mounds. — Swiss Lake-dwellings. —
Periods of Stone, Bronze, and Iron. — Post-pliocene Formations. —
Coexistence of Man with extinct Mammalia. — Reindeer Period of South
of France. — Alluvial Deposits of Paleolithic Age. — Higher and Lower-
level Valley-gravels. — Loess or Inundation-mud of the Nile, Rhine, etc. —
Origin of Caverns. — Remains of Man and extinct Quadrupeds in Cavern
Deposits. — Cave of Kirkdale. — Australian Cave-breccias. —
Geographical Relationship of the Provinces of living Vertebrata and those
of extinct Post-pliocene Species. — Extinct struthious Birds of New
Zealand. — Climate of the Post-pliocene Period. — Comparative Longevity
of Species in the Mammalia and Testacea. — Teeth of Recent and Post-
pliocene Mammalia.

Chapter XI—POST-PLIOCENE PERIOD, continued.—GLACIAL
CONDITIONS.
Geographical Distribution, Form, and Characters of Glacial Drift. —
Fundamental Rocks, polished, grooved, and scratched. — Abrading and
striating Action of Glaciers. — Moraines, Erratic Blocks, and “Roches
Moutonnees”. — Alpine Blocks on the Jura. — Continental Ice of
Greenland. — Ancient Centres of the Dispersion of Erratics. —
Transportation of Drift by floating Icebergs. — Bed of the Sea furrowed
and polished by the running aground of floating Ice-islands.
Chapter XII—POST-PLIOCENE PERIOD, continued.—GLACIAL
CONDITIONS, concluded.
Glaciation of Scandinavia and Russia. — Glaciation of Scotland. —
Mammoth in Scotch Till. — Marine Shells in Scotch Glacial Drift. — Their
Arctic Character. — Rarity of Organic Remains in Glacial Deposits. —
Contorted Strata in Drift. — Glaciation of Wales, England, and Ireland. —
Marine Shells of Moel Tryfaen. — Erratics near Chichester. — Glacial
Formations of North America. — Many Species of Testacea and
Quadrupeds survived the Glacial Cold. — Connection of the Predominance
of Lakes with Glacial Action. — Action of Ice in preventing the silting up
of Lake-basins. — Absence of Lakes in the Caucasus. — Equatorial Lakes
of Africa.
Chapter XIII—PLIOCENE PERIOD.
Glacial Formations of Pliocene Age. — Bridlington Beds. — Glacial Drifts
of Ireland. — Drift of Norfolk Cliffs. — Cromer Forest-bed. — Aldeby and
Chillesford Beds. — Norwich Crag. — Older Pliocene Strata. — Red Crag
of Suffolk. — Coprolitic Bed of Red Crag. — White or Coralline Crag. —
Relative Age, Origin, and Climate of the Crag Deposits. — Antwerp Crag.
— Newer Pliocene Strata of Sicily. — Newer Pliocene Strata of the Upper
Val d’Arno. — Older Pliocene of Italy. — Subapennine Strata. — Older
Pliocene Flora of Italy.
Chapter XIV—MIOCENE PERIOD.—UPPER MIOCENE.
Upper Miocene Strata of France. — Faluns of Touraine. — Tropical
Climate implied by Testacea. — Proportion of recent Species of Shells. —
faluns more ancient than the Suffolk Crag. — Upper Miocene of Bordeaux
and the South of France. — Upper Miocene of Oeningen, in Switzerland.
— Plants of the Upper Fresh-water Molasse. — Fossil Fruit and Flowers as

well as Leaves. — Insects of the Upper Molasse. — Middle or Marine
Molasse of Switzerland. — Upper Miocene Beds of the Bolderberg, in
Belgium. — Vienna Basin. — Upper Miocene of Italy and Greece. —
Upper Miocene of India; Siwalik Hills. — Older Pliocene and Miocene of
the United States.
Chapter XV—LOWER MIOCENE.
Lower Miocene Strata of France. — Line between Miocene and Eocene. —
Lacustrine Strata of Auvergne. — Fossil Mammalia of the Limagne
d’Auvergne. — Lower Molasse of Switzerland. — Dense Conglomerates
and Proofs of Subsidence. — Flora of the Lower Molasse. — American
Character of the Flora. — Theory of a Miocene Atlantis. — Lower Miocene
of Belgium. — Rupelian Clay of Hermsdorf near Berlin. — Mayence
Basin. — Lower Miocene of Croatia. — Oligocene Strata of Beyrich. —
Lower Miocene of Italy. — Lower Miocene of England. — Hempstead
Beds. — Bovey Tracey Lignites in Devonshire. — Isle of Mull Leaf-Beds.
— Arctic Miocene Flora. — Disco Island. — Lower Miocene of United
States. — Fossils of Nebraska.
Chapter XVI—EOCENE FORMATIONS.
Eocene Areas of North of Europe. — Table of English and French Eocene
Strata. — Upper Eocene of England. — Bembridge Beds. — Osborne or St.
Helen’s Beds. — Headon Series. — Fossils of the Barton Sands and Clays.
— Middle Eocene of England. — Shells, Nummulites, Fish and Reptiles of
the Bracklesham Beds and Bagshot Sands. — Plants of Alum Bay and
Bournemouth. — Lower Eocene of England. — London Clay Fossils. —
Woolwich and Reading Beds formerly called “Plastic Clay”. — Fluviatile
Beds underlying Deep-sea Strata. — Thanet Sands. — Upper Eocene Strata
of France. — Gypseous Series of Montmartre and Extinct Quadrupeds. —
Fossil Footprints in Paris Gypsum. — Imperfection of the Record. —
Calcaire Silicieux. — Gres de Beauchamp. — Calcaire Grossier. —
Miliolite Limestone. — Soissonnais Sands. — Lower Eocene of France. —
Nummulitic Formations of Europe, Africa, and Asia. — Eocene Strata in
the United States. — Gigantic Cetacean.
Chapter XVII—UPPER CRETACEOUS GROUP.
Lapse of Time between Cretaceous and Eocene Periods. — Table of
successive Cretaceous Formations. — Maestricht Beds. — Pisolitic
Limestone of France. — Chalk of Faxoe. — Geographical Extent and

Origin of the White Chalk. — Chalky Matter now forming in the Bed of the
Atlantic. — Marked Difference between the Cretaceous and existing Fauna.
— Chalk-flints. — Pot-stones of Horstead. — Vitreous Sponges in the
Chalk. — Isolated Blocks of Foreign Rocks in the White Chalk supposed to
be ice-borne. — Distinctness of Mineral Character in contemporaneous
Rocks of the Cretaceous Epoch. — Fossils of the White Chalk. — Lower
White Chalk without Flints. — Chalk Marl and its Fossils. — Chloritic
Series or Upper Greensand. — Coprolite Bed near Cambridge. — Fossils of
the Chloritic Series. — Gault. — Connection between Upper and Lower
Cretaceous Strata. — Blackdown Beds. — Flora of the Upper Cretaceous
Period. — Hippurite Limestone. — Cretaceous Rocks in the United States.
Chapter XVIII—LOWER CRETACEOUS OR NEOCOMIAN
FORMATION.
Classification of marine and fresh-water Strata. — Upper Neocomian. —
Folkestone and Hythe Beds. — Atherfield Clay. — Similarity of Conditions
causing Reappearance of Species after short Intervals. — Upper Speeton
Clay. — Middle Neocomian. — Tealby Series. — Middle Speeton Clay. —
Lower Neocomian. — Lower Speeton Clay. — Wealden Formation. —
Fresh-water Character of the Wealden. — Weald Clay. — Hastings Sands.
— Punfield Beds of Purbeck, Dorsetshire. — Fossil Shells and Fish of the
Wealden. — Area of the Wealden. — Flora of the Wealden.
Chapter XIX—JURASSIC GROUP.—PURBECK BEDS AND
OOLITE.
The Purbeck Beds a Member of the Jurassic Group. — Subdivisions of that
Group. — Physical Geography of the Oolite in England and France. —
Upper Oolite. — Purbeck Beds. — New Genera of fossil Mammalia in the
Middle Purbeck of Dorsetshire. — Dirt-bed or ancient Soil. — Fossils of
the Purbeck Beds. — Portland Stone and Fossils. — Kimmeridge Clay. —
Lithographic Stone of Solenhofen. — Archæopteryx. — Middle Oolite. —
Coral Rag. — Nerinæa Limestone. — Oxford Clay, Ammonites and
Belemnites. — Kelloway Rock. — Lower, or Bath, Oolite. — Great Plants
of the Oolite. — Oolite and Bradford Clay. — Stonesfield Slate. — Fossil
Mammalia. — Fuller’s Earth. — Inferior Oolite and Fossils. —
Northamptonshire Slates. — Yorkshire Oolitic Coal-field. — Brora Coal. —
Palæontological Relations of the several Subdivisions of the Oolitic group.

Chapter XX—JURASSIC GROUP, CONTINUED.—LIAS.
Mineral Character of Lias. — Numerous successive Zones in the Lias,
marked by distinct Fossils, without Unconformity in the Stratification, or
Change in the Mineral Character of the Deposits. — Gryphite Limestone.
— Shells of the Lias. — Fish of the Lias. — Reptiles of the Lias. —
Ichthyosaur and Plesiosaur. — Marine Reptile of the Galapagos Islands. —
Sudden Destruction and Burial of Fossil Animals in Lias. — Fluvio-marine
Beds in Gloucestershire, and Insect Limestone. — Fossil Plants. — The
origin of the Oolite and Lias, and of alternating Calcareous and
Argillaceous Formations.
Chapter XXI—TRIAS, OR NEW RED SANDSTONE GROUP.
Beds of Passage between the Lias and Trias, Rhætic Beds. — Triassic
Mammifer. — Triple Division of the Trias. — Keuper, or Upper Trias of
England. — Reptiles of the Upper Trias. — Foot-prints in the Bunter
formation in England. — Dolomitic Conglomerate of Bristol. — Origin of
Red Sandstone and Rock-salt. — Precipitation of Salt from inland Lakes
and Lagoons. — Trias of Germany. — Keuper. — St. Cassian and Hallstadt
Beds. — Peculiarity of their Fauna. — Muschelkalk and its Fossils. — Trias
of the United States. — Fossil Foot-prints of Birds and Reptiles in the
Valley of the Connecticut. — Triassic Mammifer of North Carolina. —
Triassic Coal-field of Richmond, Virginia. — Low Grade of early Mammals
favourable to the Theory of Progressive Development.
Chapter XXII—PERMIAN OR MAGNESIAN LIMESTONE GROUP.
Line of Separation between Mesozoic and Palæozoic Rocks. —
Distinctness of Triassic and Permian Fossils. — Term Permian. —
Thickness of calcareous and sedimentary Rocks in North of England. —
Upper, Middle, and Lower Permian. — Marine Shells and Corals of the
English Magnesian Limestone. — Reptiles and Fish of Permian Marl-slate.
— Foot-prints of Reptiles. — Angular Breccias in Lower Permian. —
Permian Rocks of the Continent. — Zechstein and Rothliegendes of
Thuringia. — Permian Flora. — Its generic Affinity to the Carboniferous.
Chapter XXIII—THE COAL OR CARBONIFEROUS GROUP.
Principal Subdivisions of the Carboniferous Group. — Different Thickness
of the sedimentary and calcareous Members in Scotland and the South of
England. — Coal-measures. — Terrestrial Nature of the Growth of Coal. —
Erect fossil Trees. — Uniting of many Coal-seams into one thick Bed. —

Purity of the Coal explained. — Conversion of Coal into Anthracite. —
Origin of Clay-ironstone. — Marine and brackish-water Strata in Coal. —
Fossil Insects. — Batrachian Reptiles. — Labyrinthodont Foot-prints in
Coal-measures. — Nova Scotia Coal-measures with successive Growths of
erect fossil Trees. — Similarity of American and European Coal. — Air-
breathers of the American Coal. — Changes of Condition of Land and Sea
indicated by the Carboniferous Strata of Nova Scotia.
Chapter XXIV—FLORA AND FAUNA OF THE CARBONIFEROUS
PERIOD.
Vegetation of the Coal Period. — Ferns, Lycopodiaceæ, Equisetaceæ,
Sigillariæ, Stigmariæ, Coniferæ. — Angiosperms. — Climate of the Coal
Period. — Mountain Limestone. — Marine Fauna of the Carboniferous
Period. — Corals. — Bryozoa, Crinoidea. — Mollusca. — Great Number
of fossil Fish. — Foraminifera.
Chapter XXV—DEVONIAN OR OLD RED SANDSTONE GROUP.
Classification of the Old Red Sandstone in Scotland and in Devonshire. —
Upper Old Red Sandstone in Scotland, with Fish and Plants. — Middle Old
Red Sandstone. — Classification of the Ichthyolites of the Old Red, and
their Relation to Living Types. — Lower Old Red Sandstone, with
Cephalaspis and Pterygotus. — Marine or Devonian Type of Old Red
Sandstone. — Table of Devonian Series. — Upper Devonian Rocks and
Fossils. — Middle. — Lower. — Eifel Limestone of Germany. — Devonian
of Russia. — Devonian Strata of the United States and Canada. —
Devonian Plants and Insects of Canada.
Chapter XXVI—SILURIAN GROUP.
Classification of the Silurian Rocks. — Ludlow Formation and Fossils. —
Bone-bed of the Upper Ludlow. — Lower Ludlow Shales with Pentamerus.
— Oldest known Remains of fossil Fish. — Table of the progressive
Discovery of Vertebrata in older Rocks. — Wenlock Formation, Corals,
Cystideans and Trilobites. — Llandovery Group or Beds of Passage. —
Lower Silurian Rocks. — Caradoc and Bala Beds. — Brachiopoda. —
Trilobites. — Cystideæ. — Graptolites. — Llandeilo Flags. — Arenig or
Stiper-stones Group. — Foreign Silurian Equivalents in Europe. — Silurian
Strata of the United States. — Canadian Equivalents. — Amount of specific
Agreement of Fossils with those of Europe.

Chapter XXVII—CAMBRIAN AND LAURENTIAN GROUPS.
Classification of the Cambrian Group, and its Equivalent in Bohemia. —
Upper Cambrian Rocks. — Tremadoc Slates and their Fossils. — Lingula
Flags. — Lower Cambrian Rocks. — Menevian Beds. — Longmynd
Group. — Harlech Grits with large Trilobites. — Llanberis Slates. —
Cambrian Rocks of Bohemia. — Primordial Zone of Barrande. —
Metamorphosis of Trilobites. — Cambrian Rocks of Sweden and Norway.
— Cambrian Rocks of the United States and Canada. — Potsdam
Sandstone. — Huronian Series. — Laurentian Group, upper and lower. —
Eozoon Canadense, oldest known Fossil. — Fundamental Gneiss of
Scotland.
Chapter XXVIII—VOLCANIC ROCKS.
External Form, Structure, and Origin of Volcanic Mountains. — Cones and
Craters. — Hypothesis of “Elevation Craters” considered. — Trap Rocks.
— Name whence derived. — Minerals most abundant in Volcanic Rocks.
— Table of the Analysis of Minerals in the Volcanic and Hypogene Rocks.
— Similar Minerals in Meteorites. — Theory of Isomorphism. — Basaltic
Rocks. — Trachytic Rocks. — Special Forms of Structure. — The
columnar and globular Forms. — Trap Dikes and Veins. — Alteration of
Rocks by volcanic Dikes. — Conversion of Chalk into Marble. — Intrusion
of Trap between Strata. — Relation of trappean Rocks to the Products of
active Volcanoes.
Chapter XXIX—ON THE AGES OF VOLCANIC ROCKS.
Tests of relative Age of Volcanic Rocks. — Why ancient and modern Rocks
cannot be identical. — Tests by Superposition and intrusion. — Test by
Alteration of Rocks in Contact. — Test by Organic Remains. — Test of Age
by Mineral Character. — Test by Included Fragments. — Recent and Post-
pliocene volcanic Rocks. — Vesuvius, Auvergne, Puy de Come, and Puy de
Pariou. — Newer Pliocene volcanic Rocks. — Cyclopean Isles, Etna, Dikes
of Palagonia, Madeira. — Older Pliocene volcanic Rocks. — Italy. —
Pliocene Volcanoes of the Eifel. — Trass.
Chapter XXX—AGE OF VOLCANIC ROCKS—CONTINUED.
Volcanic Rocks of the Upper Miocene Period. — Madeira. — Grand
Canary. — Azores. — Lower Miocene Volcanic Rocks. — Isle of Mull. —
Staffa and Antrim. — The Eifel. — Upper and Lower Miocene Volcanic
Rocks of Auvergne. — Hill of Gergovia. — Eocene Volcanic Rocks of

Monte Bolca. — Trap of Cretaceous Period. — Oolitic Period. — Triassic
Period. — Permian Period. — Carboniferous Period. — Erect Trees buried
in Volcanic Ash in the Island of Arran. — Old Red Sandstone Period. —
Silurian Period. — Cambrian Period. — Laurentian Volcanic Rocks.
Chapter XXXI—PLUTONIC ROCKS.
General Aspect of Plutonic Rocks. — Granite and its Varieties. —
Decomposing into Spherical Masses. — Rude columnar Structure. —
Graphic Granite. — Mutual Penetration of Crystals of Quartz and Feldspar.
— Glass Cavities in Quartz of Granite. — Porphyritic, talcose, and syenitic
Granite. — Schorlrock and Eurite. — Syenite. — Connection of the
Granites and Syenites with the Volcanic Rocks. — Analogy in Composition
of Trachyte and Granite. — Granite Veins in Glen Tilt, Cape of Good Hope,
and Cornwall. — Metalliferous Veins in Strata near their Junction with
Granite. — Quartz Veins. — Exposure of Plutonic Rocks at the surface due
to Denudation.
Chapter XXXII—ON THE DIFFERENT AGES OF THE PLUTONIC
ROCKS.
Difficulty in ascertaining the precise Age of a Plutonic Rock. — Test of Age
by Relative Position. — Test by Intrusion and Alteration. — Test by
Mineral Composition. — Test by included Fragments. — Recent and
Pliocene Plutonic Rocks, why invisible. — Miocene Syenite of the Isle of
Skye. — Eocene Plutonic Rocks in the Andes. — Granite altering
Cretaceous Rocks. — Granite altering Lias in the Alps and in Skye. —
Granite of Dartmoor altering Carboniferous Strata. — Granite of the Old
Red Sandstone Period. — Syenite altering Silurian Strata in Norway. —
Blending of the same with Gneiss. — Most ancient Plutonic Rocks. —
Granite protruded in a solid Form.
Chapter XXXIII—METAMORPHIC ROCKS.
General Character of Metamorphic Rocks. — Gneiss. — Hornblende-
schist. — Serpentine. — Mica-schist. — Clay-slate. — Quartzite. —
Chlorite-schist. — Metamorphic Limestone. — Origin of the metamorphic
Strata. — Their Stratification. — Fossiliferous Strata near intrusive Masses
of Granite converted into Rocks identical with different Members of the
metamorphic Series. — Arguments hence derived as to the Nature of
Plutonic Action. — Hydrothermal Action, or the Influence of Steam and

Gases in producing Metamorphism. — Objections to the metamorphic
Theory considered.
Chapter XXXIV—METAMORPHIC ROCKS—continued.
Definition of slaty Cleavage and Joints. — Supposed Causes of these
Structures. — Crystalline Theory of Cleavage. — Mechanical Theory of
Cleavage. — Condensation and Elongation of slate Rocks by lateral
Pressure. — Lamination of some volcanic Rocks due to Motion. —
Whether the Foliation of the crystalline Schists be usually parallel with the
original Planes of Stratification. — Examples in Norway and Scotland. —
Causes of Irregularity in the Planes of Foliation.
Chapter XXXV—ON THE DIFFERENT AGES OF THE
METAMORPHIC ROCKS.
Difficulty of ascertaining the Age of metamorphic Strata. — Metamorphic
Strata of Eocene date in the Alps of Switzerland and Savoy. — Limestone
and Shale of Carrara. — Metamorphic Strata of older date than the Silurian
and Cambrian Rocks. — Order of Succession in metamorphic Rocks. —
Uniformity of mineral Character. — Supposed Azoic Period. — Connection
between the Absence of Organic Remains and the Scarcity of calcareous
Matter in metamorphic Rocks.
Chapter XXXVI—MINERAL VEINS.
Different Kinds of mineral Veins. — Ordinary metalliferous Veins or Lodes.
— Their frequent Coincidence with Faults. — Proofs that they originated in
Fissures in solid Rock. — Veins shifting other Veins. — Polishing of their
Walls or “Slicken sides”. — Shells and Pebbles in Lodes. — Evidence of
the successive Enlargement and Reopening of veins. — Examples in
Cornwall and in Auvergne. — Dimensions of Veins. — Why some
alternately swell out and contract. — Filling of Lodes by Sublimation from
below. — Supposed relative Age of the precious Metals. — Copper and
lead Veins in Ireland older than Cornish Tin. — Lead Vein in Lias,
Glamorganshire. — Gold in Russia, California, and Australia. —
Connection of hot Springs and mineral Veins.
INDEX

PREFACE.

THE LAST or sixth EDITION of my “Elements of Geology” was already out
of print before the end of 1868, in which year I brought out the tenth edition
of my “Principles of Geology.”
In writing the last-mentioned work I had been called upon to pass in
review almost all the leading points of speculation and controversy to which
the rapid advance of the science had given rise, and when I proposed to
bring out a new edition of the “Elements” I was strongly urged by my
friends not to repeat these theoretical discussions, but to confine myself in
the new treatise to those parts of the “Elements” which were most
indispensable to a beginner. This was to revert, to a certain extent, to the
original plan of the first edition; but I found, after omitting a great number
of subjects, that the necessity of bringing up to the day those which
remained, and adverting, however briefly, to new discoveries, made it most
difficult to confine the proposed abridgment within moderate limits. Some
chapters had to be entirely recast, some additional illustrations to be
introduced, and figures of some organic remains to be replaced by new ones
from specimens more perfect than those which had been at my command on
former occasions. By these changes the work assumed a form so different
from the sixth edition of the “Elements,” that I resolved to give it a new title
and call it the “Student’s Elements of Geology.”
In executing this task I have found it very difficult to meet the
requirements of those who are entirely ignorant of the science. It is only the
adept who has already overcome the first steps as an observer, and is
familiar with many of the technical terms, who can profit by a brief and
concise manual. Beginners wish for a short and cheap book in which they
may find a full explanation of the leading facts and principles of Geology.
Their wants, I fear, somewhat resemble those of the old woman in New
England, who asked a bookseller to supply her with “the cheapest Bible in
the largest possible print.”

But notwithstanding the difficulty of reconciling brevity with the
copiousness of illustration demanded by those who have not yet mastered
the rudiments of the science, I have endeavoured to abridge the work in the
manner above hinted at, so as to place it within the reach of many to whom
it was before inaccessible.

CHARLES LYELL.

73 HARLEY STREET, LONDON,
December, 1870.

CHAPTER I.
ON THE DIFFERENT CLASSES OF ROCKS.

Geology defined. — Successive Formation of the Earth’s
Crust. — Classification of Rocks according to their Origin
and Age. — Aqueous Rocks. — Their Stratification and
imbedded Fossils. — Volcanic Rocks, with and without
Cones and Craters. — Plutonic Rocks, and their Relation to
the Volcanic. — Metamorphic Rocks, and their probable
Origin. — The term Primitive, why erroneously applied to
the Crystalline Formations. — Leading Division of the
Work.

Of what materials is the earth composed, and in what manner are these
materials arranged? These are the first inquiries with which Geology is
occupied, a science which derives its name from the Greek ge, the earth,
and logos, a discourse. Previously to experience we might have imagined
that investigations of this kind would relate exclusively to the mineral
kingdom, and to the various rocks, soils, and metals, which occur upon the
surface of the earth, or at various depths beneath it. But, in pursuing such
researches, we soon find ourselves led on to consider the successive
changes which have taken place in the former state of the earth’s surface
and interior, and the causes which have given rise to these changes; and,
what is still more singular and unexpected, we soon become engaged in
researches into the history of the animate creation, or of the various tribes
of animals and plants which have, at different periods of the past, inhabited
the globe.
All are aware that the solid parts of the earth consist of distinct
substances, such as clay, chalk, sand, limestone, coal, slate, granite, and the
like; but previously to observation it is commonly imagined that all these

had remained from the first in the state in which we now see them—that
they were created in their present form, and in their present position. The
geologist soon comes to a different conclusion, discovering proofs that the
external parts of the earth were not all produced in the beginning of things
in the state in which we now behold them, nor in an instant of time. On the
contrary, he can show that they have acquired their actual configuration and
condition gradually, under a great variety of circumstances, and at
successive periods, during each of which distinct races of living beings
have flourished on the land and in the waters, the remains of these creatures
still lying buried in the crust of the earth.
By the “earth’s crust,” is meant that small portion of the exterior of our
planet which is accessible to human observation. It comprises not merely all
of which the structure is laid open in mountain precipices, or in cliffs
overhanging a river or the sea, or whatever the miner may reveal in
artificial excavations; but the whole of that outer covering of the planet on
which we are enabled to reason by observations made at or near the surface.
These reasonings may extend to a depth of several miles, perhaps ten miles;
and even then it may be said, that such a thickness is no more than 1/400
part of the distance from the surface to the centre. The remark is just: but
although the dimensions of such a crust are, in truth, insignificant when
compared to the entire globe, yet they are vast, and of magnificent extent in
relation to man, and to the organic beings which people our globe.
Referring to this standard of magnitude, the geologist may admire the
ample limits of his domain, and admit, at the same time, that not only the
exterior of the planet, but the entire earth, is but an atom in the midst of the
countless worlds surveyed by the astronomer.
The materials of this crust are not thrown together confusedly; but
distinct mineral masses, called rocks, are found to occupy definite spaces,
and to exhibit a certain order of arrangement. The term rock is applied
indifferently by geologists to all these substances, whether they be soft or
stony, for clay and sand are included in the term, and some have even
brought peat under this denomination. Our old writers endeavoured to avoid
offering such violence to our language, by speaking of the component
materials of the earth as consisting of rocks and soils. But there is often so
insensible a passage from a soft and incoherent state to that of stone, that
geologists of all countries have found it indispensable to have one technical
term to include both, and in this sense we find roche applied in French,

rocca in Italian, and felsart in German. The beginner, however, must
constantly bear in mind that the term rock by no means implies that a
mineral mass is in an indurated or stony condition.
The most natural and convenient mode of classifying the various rocks
which compose the earth’s crust, is to refer, in the first place, to their origin,
and in the second to their relative age. I shall therefore begin by
endeavouring briefly to explain to the student how all rocks may be divided
into four great classes by reference to their different origin, or, in other
words, by reference to the different circumstances and causes by which they
have been produced.
The first two divisions, which will at once be understood as natural, are
the aqueous and volcanic, or the products of watery and those of igneous
action at or near the surface.
Aqueous Rocks.—The aqueous rocks, sometimes called the
sedimentary, or fossiliferous, cover a larger part of the earth’s surface than
any others. They consist chiefly of mechanical deposits (pebbles, sand, and
mud), but are partly of chemical and some of them of organic origin,
especially the limestones. These rocks are stratified, or divided into distinct
layers, or strata. The term stratum means simply a bed, or any thing spread
out or strewed over a given surface; and we infer that these strata have been
generally spread out by the action of water, from what we daily see taking
place near the mouths of rivers, or on the land during temporary
inundations. For, whenever a running stream charged with mud or sand, has
its velocity checked, as when it enters a lake or sea, or overflows a plain,
the sediment, previously held in suspension by the motion of the water,
sinks, by its own gravity to the bottom. In this manner layers of mud and
sand are thrown down one upon another.
If we drain a lake which has been fed by a small stream, we frequently
find at the bottom a series of deposits, disposed with considerable
regularity, one above the other; the uppermost, perhaps, may be a stratum of
peat, next below a more dense and solid variety of the same material; still
lower a bed of shell-marl, alternating with peat or sand, and then other beds
of marl, divided by layers of clay. Now, if a second pit be sunk through the
same continuous lacustrine formation at some distance from the first, nearly
the same series of beds is commonly met with, yet with slight variations;
some, for example, of the layers of sand, clay, or marl, may be wanting, one

or more of them having thinned out and given place to others, or sometimes
one of the masses first examined is observed to increase in thickness to the
exclusion of other beds.
The term formation, which I have used in the above explanation,
expresses in geology any assemblage of rocks which have some character in
common, whether of origin, age, or composition. Thus we speak of
stratified and unstratified, fresh-water and marine, aqueous and volcanic,
ancient and modern, metalliferous and non-metalliferous formations.
In the estuaries of large rivers, such as the Ganges and the Mississippi,
we may observe, at low water, phenomena analogous to those of the drained
lakes above mentioned, but on a grander scale, and extending over areas
several hundred miles in length and breadth. When the periodical
inundations subside, the river hollows out a channel to the depth of many
yards through horizontal beds of clay and sand, the ends of which are seen
exposed in perpendicular cliffs. These beds vary in their mineral
composition, or colour, or in the fineness or coarseness of their particles,
and some of them are occasionally characterised by containing drift-wood.
At the junction of the river and the sea, especially in lagoons nearly
separated by sand-bars from the ocean, deposits are often formed in which
brackish and salt-water shells are included.
In Egypt, where the Nile is always adding to its delta by filling up part of
the Mediterranean with mud, the newly deposited sediment is stratified, the
thin layer thrown down in one season differing slightly in colour from that
of a previous year, and being separable from it, as has been observed in
excavations at Cairo and other places.[1]
When beds of sand, clay, and marl, containing shells and vegetable
matter, are found arranged in a similar manner in the interior of the earth,
we ascribe to them a similar origin; and the more we examine their
characters in minute detail, the more exact do we find the resemblance.
Thus, for example, at various heights and depths in the earth, and often far
from seas, lakes, and rivers, we meet with layers of rounded pebbles
composed of flint, limestone, granite, or other rocks, resembling the
shingles of a sea-beach or the gravel in a torrent’s bed. Such layers of
pebbles frequently alternate with others formed of sand or fine sediment,
just as we may see in the channel of a river descending from hills bordering
a coast, where the current sweeps down at one season coarse sand and

gravel, while at another, when the waters are low and less rapid, fine mud
and sand alone are carried seaward.[2]
If a stratified arrangement, and the rounded form of pebbles, are alone
sufficient to lead us to the conclusion that certain rocks originated under
water, this opinion is farther confirmed by the distinct and independent
evidence of fossils, so abundantly included in the earth’s crust. By a fossil is
meant any body, or the traces of the existence of any body, whether animal
or vegetable, which has been buried in the earth by natural causes. Now the
remains of animals, especially of aquatic species, are found almost
everywhere imbedded in stratified rocks, and sometimes, in the case of
limestone, they are in such abundance as to constitute the entire mass of the
rock itself. Shells and corals are the most frequent, and with them are often
associated the bones and teeth of fishes, fragments of wood, impressions of
leaves, and other organic substances. Fossil shells, of forms such as now
abound in the sea, are met with far inland, both near the surface, and at
great depths below it. They occur at all heights above the level of the ocean,
having been observed at elevations of more than 8000 feet in the Pyrenees,
10,000 in the Alps, 13,000 in the Andes, and above 18,000 feet in the
Himalaya.[3]
These shells belong mostly to marine testacea, but in some places
exclusively to forms characteristic of lakes and rivers. Hence it is concluded
that some ancient strata were deposited at the bottom of the sea, and others
in lakes and estuaries.
We have now pointed out one great class of rocks, which, however they
may vary in mineral composition, colour, grain, or other characters, external
and internal, may nevertheless be grouped together as having a common
origin. They have all been formed under water, in the same manner as
modern accumulations of sand, mud, shingle, banks of shells, reefs of coral,
and the like, and are all characterised by stratification or fossils, or by both.
Volcanic Rocks.—The division of rocks which we may next consider are
the volcanic, or those which have been produced at or near the surface
whether in ancient or modern times, not by water, but by the action of fire
or subterranean heat. These rocks are for the most part unstratified, and are
devoid of fossils. They are more partially distributed than aqueous
formations, at least in respect to horizontal extension. Among those parts of
Europe where they exhibit characters not to be mistaken, I may mention not

only Sicily and the country round Naples, but Auvergne, Velay, and
Vivarais, now the departments of Puy de Dome, Haute Loire, and Ardêche,
towards the centre and south of France, in which are several hundred
conical hills having the forms of modern volcanoes, with craters more or
less perfect on many of their summits. These cones are composed moreover
of lava, sand, and ashes, similar to those of active volcanoes. Streams of
lava may sometimes be traced from the cones into the adjoining valleys,
where they have choked up the ancient channels of rivers with solid rock, in
the same manner as some modern flows of lava in Iceland have been known
to do, the rivers either flowing beneath or cutting out a narrow passage on
one side of the lava. Although none of these French volcanoes have been in
activity within the period of history or tradition, their forms are often very
perfect. Some, however, have been compared to the mere skeletons of
volcanoes, the rains and torrents having washed their sides, and removed all
the loose sand and scoriæ, leaving only the harder and more solid materials.
By this erosion, and by earthquakes, their internal structure has occasionally
been laid open to view, in fissures and ravines; and we then behold not only
many successive beds and masses of porous lava, sand, and scoriæ, but also
perpendicular walls, or dikes, as they are called, of volcanic rock, which
have burst through the other materials. Such dikes are also observed in the
structure of Vesuvius, Etna, and other active volcanoes. They have been
formed by the pouring of melted matter, whether from above or below, into
open fissures, and they commonly traverse deposits of volcanic tuff, a
substance produced by the showering down from the air, or incumbent
waters, of sand and cinders, first shot up from the interior of the earth by the
explosions of volcanic gases.
Besides the parts of France above alluded to, there are other countries, as
the north of Spain, the south of Sicily, the Tuscan territory of Italy, the
lower Rhenish provinces, and Hungary, where spent volcanoes may be
seen, still preserving in many cases a conical form, and having craters and
often lava-streams connected with them.
There are also other rocks in England, Scotland, Ireland, and almost
every country in Europe, which we infer to be of igneous origin, although
they do not form hills with cones and craters. Thus, for example, we feel
assured that the rock of Staffa, and that of the Giant’s Causeway, called
basalt, is volcanic, because it agrees in its columnar structure and mineral
composition with streams of lava which we know to have flowed from the

craters of volcanoes. We find also similar basaltic and other igneous rocks
associated with beds of tuff in various parts of the British Isles, and forming
dikes, such as have been spoken of; and some of the strata through which
these dikes cut are occasionally altered at the point of contact, as if they had
been exposed to the intense heat of melted matter.
The absence of cones and craters, and long narrow streams of superficial
lava, in England and many other countries, is principally to be attributed to
the eruptions having been submarine, just as a considerable proportion of
volcanoes in our own times burst out beneath the sea. But this question
must be enlarged upon more fully in the chapters on Igneous Rocks, in
which it will also be shown, that as different sedimentary formations,
containing each their characteristic fossils, have been deposited at
successive periods, so also volcanic sand and scoriæ have been thrown out,
and lavas have flowed over the land or bed of the sea, at many different
epochs, or have been injected into fissures; so that the igneous as well as the
aqueous rocks may be classed as a chronological series of monuments,
throwing light on a succession of events in the history of the earth.
Plutonic Rocks (Granite, etc).—We have now pointed out the existence
of two distinct orders of mineral masses, the aqueous and the volcanic: but
if we examine a large portion of a continent, especially if it contain within it
a lofty mountain range, we rarely fail to discover two other classes of rocks,
very distinct from either of those above alluded to, and which we can
neither assimilate to deposits such as are now accumulated in lakes or seas,
nor to those generated by ordinary volcanic action. The members of both
these divisions of rocks agree in being highly crystalline and destitute of
organic remains. The rocks of one division have been called Plutonic,
comprehending all the granites and certain porphyries, which are nearly
allied in some of their characters to volcanic formations. The members of
the other class are stratified and often slaty, and have been called by some
the crystalline schists, in which group are included gneiss, micaceous-schist
(or mica-slate), hornblende-schist, statuary marble, the finer kinds of
roofing slate, and other rocks afterwards to be described.
As it is admitted that nothing strictly analogous to these crystalline
productions can now be seen in the progress of formation on the earth’s
surface, it will naturally be asked, on what data we can find a place for them
in a system of classification founded on the origin of rocks. I cannot, in

reply to this question, pretend to give the student, in a few words, an
intelligible account of the long chain of facts and reasonings from which
geologists have been led to infer the nature of the rocks in question. The
result, however, may be briefly stated. All the various kinds of granites
which constitute the Plutonic family are supposed to be of igneous or
aqueo-igneous origin, and to have been formed under great pressure, at a
considerable depth in the earth, or sometimes, perhaps, under a certain
weight of incumbent ocean. Like the lava of volcanoes, they have been
melted, and afterwards cooled and crystallised, but with extreme slowness,
and under conditions very different from those of bodies cooling in the open
air. Hence they differ from the volcanic rocks, not only by their more
crystalline texture, but also by the absence of tuffs and breccias, which are
the products of eruptions at the earth’s surface, or beneath seas of
inconsiderable depth. They differ also by the absence of pores or cellular
cavities, to which the expansion of the entangled gases gives rise in
ordinary lava.
Metamorphic, or Stratified Crystalline Rocks.—The fourth and last
great division of rocks are the crystalline strata and slates, or schists, called
gneiss, mica-schist, clay-slate, chlorite-schist, marble, and the like, the
origin of which is more doubtful than that of the other three classes. They
contain no pebbles, or sand, or scoriæ, or angular pieces of imbedded stone,
and no traces of organic bodies, and they are often as crystalline as granite,
yet are divided into beds, corresponding in form and arrangement to those
of sedimentary formations, and are therefore said to be stratified. The beds
sometimes consist of an alternation of substances varying in colour,
composition, and thickness, precisely as we see in stratified fossiliferous
deposits. According to the Huttonian theory, which I adopt as the most
probable, and which will be afterwards more fully explained, the materials
of these strata were originally deposited from water in the usual form of
sediment, but they were subsequently so altered by subterranean heat, as to
assume a new texture. It is demonstrable, in some cases at least, that such a
complete conversion has actually taken place, fossiliferous strata having
exchanged an earthy for a highly crystalline texture for a distance of a
quarter of a mile from their contact with granite. In some cases, dark
limestones, replete with shells and corals, have been turned into white
statuary marble; and hard clays, containing vegetable or other remains, into

slates called mica-schist or hornblende-schist, every vestige of the organic
bodies having been obliterated.
Although we are in a great degree ignorant of the precise nature of the
influence exerted in these cases, yet it evidently bears some analogy to that
which volcanic heat and gases are known to produce; and the action may be
conveniently called Plutonic, because it appears to have been developed in
those regions where Plutonic rocks are generated, and under similar
circumstances of pressure and depth in the earth. Intensely heated water or
steam permeating stratified masses under great pressure have no doubt
played their part in producing the crystalline texture and other changes, and
it is clear that the transforming influence has often pervaded entire
mountain masses of strata.
In accordance with the hypothesis above alluded to, I proposed in the
first edition of the Principles of Geology (1833) the term “Metamorphic”
for the altered strata, a term derived from meta, trans, and morphe, forma.
Hence there are four great classes of rocks considered in reference to
their origin—the aqueous, the volcanic, the Plutonic, and the metamorphic.
In the course of this work it will be shown that portions of each of these
four distinct classes have originated at many successive periods. They have
all been produced contemporaneously, and may even now be in the progress
of formation on a large scale. It is not true, as was formerly supposed, that
all granites, together with the crystalline or metamorphic strata, were first
formed, and therefore entitled to be called “primitive,” and that the aqueous
and volcanic rocks were afterwards superimposed, and should, therefore,
rank as secondary in the order of time. This idea was adopted in the infancy
of the science, when all formations, whether stratified or unstratified, earthy
or crystalline, with or without fossils, were alike regarded as of aqueous
origin. At that period it was naturally argued that the foundation must be
older than the superstructure; but it was afterwards discovered that this
opinion was by no means in every instance a legitimate deduction from
facts; for the inferior parts of the earth’s crust have often been modified,
and even entirely changed, by the influence of volcanic and other
subterranean causes, while superimposed formations have not been in the
slightest degree altered. In other words, the destroying and renovating
processes have given birth to new rocks below, while those above, whether
crystalline or fossiliferous, have remained in their ancient condition. Even

in cities, such as Venice and Amsterdam, it cannot be laid down as
universally true that the upper parts of each edifice, whether of brick or
marble, are more modern than the foundations on which they rest, for these
often consist of wooden piles, which may have rotted and been replaced one
after the other, without the least injury to the buildings above; meanwhile,
these may have required scarcely any repair, and may have been constantly
inhabited. So it is with the habitable surface of our globe, in its relation to
large masses of rock immediately below; it may continue the same for ages,
while subjacent materials, at a great depth, are passing from a solid to a
fluid state, and then reconsolidating, so as to acquire a new texture.
As all the crystalline rocks may, in some respects, be viewed as
belonging to one great family, whether they be stratified or unstratified,
metamorphic or Plutonic, it will often be convenient to speak of them by
one common name. It being now ascertained, as above stated, that they are
of very different ages, sometimes newer than the strata called secondary, the
terms primitive and primary which were formerly used for the whole must
be abandoned, as they would imply a manifest contradiction. It is
indispensable, therefore, to find a new name, one which must not be of
chronological import, and must express, on the one hand, some peculiarity
equally attributable to granite and gneiss (to the Plutonic as well as the
altered rocks), and, on the other, must have reference to characters in which
those rocks differ, both from the volcanic and from the unaltered
sedimentary strata. I proposed in the Principles of Geology (first edition,
vol. iii) the term “hypogene” for this purpose, derived from upo, under, and
ginomai, to be, or to be born; a word implying the theory that granite,
gneiss, and the other crystalline formations are alike netherformed rocks, or
rocks which have not assumed their present form and structure at the
surface. They occupy the lowest place in the order of superposition. Even in
regions such as the Alps, where some masses of granite and gneiss can be
shown to be of comparatively modern date, belonging, for example, to the
period hereafter to be described as tertiary, they are still underlying rocks.
They never repose on the volcanic or trappean formations, nor on strata
containing organic remains. They are hypogene, as “being under” all the
rest.
From what has now been said, the reader will understand that each of the
four great classes of rocks may be studied under two distinct points of view;
first, they may be studied simply as mineral masses deriving their origin

from particular causes, and having a certain composition, form, and position
in the earth’s crust, or other characters both positive and negative, such as
the presence or absence of organic remains. In the second place, the rocks
of each class may be viewed as a grand chronological series of monuments,
attesting a succession of events in the former history of the globe and its
living inhabitants.
I shall accordingly proceed to treat of each family of rocks; first, in
reference to those characters which are not chronological, and then in
particular relation to the several periods when they were formed.
[1] See Principles of Geology, by the Author, Index, “Nile,” “Rivers,” etc.

[2] See p. 44, Fig. 7.

[3] Col. R. J. Strachey found oolitic fossils 18,400 feet high in the Himalaya.

CHAPTER II.
AQUEOUS ROCKS.—THEIR COMPOSITION
AND FORMS OF STRATIFICATION.

Mineral Composition of Strata. — Siliceous Rocks. —
Argillaceous. — Calcareous. — Gypsum. — Forms of
Stratification. — Original Horizontality. — Thinning out. —
Diagonal Arrangement. — Ripple-mark.

In pursuance of the arrangement explained in the last chapter, we shall
begin by examining the aqueous or sedimentary rocks, which are for the
most part distinctly stratified, and contain fossils. We may first study them
with reference to their mineral composition, external appearance, position,
mode of origin, organic contents, and other characters which belong to them
as aqueous formations, independently of their age, and we may afterwards
consider them chronologically or with reference to the successive
geological periods when they originated.
I have already given an outline of the data which led to the belief that the
stratified and fossiliferous rocks were originally deposited under water; but,
before entering into a more detailed investigation, it will be desirable to say
something of the ordinary materials of which such strata are composed.
These may be said to belong principally to three divisions, the siliceous, the
argillaceous, and the calcareous, which are formed respectively of flint,
clay, and carbonate of lime. Of these, the siliceous are chiefly made up of
sand or flinty grains; the argillaceous, or clayey, of a mixture of siliceous
matter with a certain proportion, about a fourth in weight, of aluminous
earth; and, lastly, the calcareous rocks, or limestones, of carbonic acid and
lime.

Siliceous and Arenaceous Rocks.—To speak first of the sandy division:
beds of loose sand are frequently met with, of which the grains consist
entirely of silex, which term comprehends all purely siliceous minerals, as
quartz and common flint. Quartz is silex in its purest form. Flint usually
contains some admixture of alumina and oxide of iron. The siliceous grains
in sand are usually rounded, as if by the action of running water. Sandstone
is an aggregate of such grains, which often cohere together without any
visible cement, but more commonly are bound together by a slight quantity
of siliceous or calcareous matter, or by oxide of iron or clay.
Pure siliceous rocks may be known by not effervescing when a drop of
nitric, sulphuric or other acid is applied to them, or by the grains not being
readily scratched or broken by ordinary pressure. In nature there is every
intermediate gradation, from perfectly loose sand to the hardest sandstone.
In micaceous sandstones mica is very abundant; and the thin silvery plates
into which that mineral divides are often arranged in layers parallel to the
planes of stratification, giving a slaty or laminated texture to the rock.
When sandstone is coarse-grained, it is usually called grit. If the grains
are rounded, and large enough to be called pebbles, it becomes a
conglomerate or pudding-stone, which may consist of pieces of one or of
many different kinds of rock. A conglomerate, therefore, is simply gravel
bound together by cement.
Argillaceous Rocks.—Clay, strictly speaking, is a mixture of silex or
flint with a large proportion, usually about one fourth, of alumina, or argil;
but in common language, any earth which possesses sufficient ductility,
when kneaded up with water, to be fashioned like paste by the hand, or by
the potter’s lathe, is called a clay; and such clays vary greatly in their
composition, and are, in general, nothing more than mud derived from the
decomposition or wearing down of rocks. The purest clay found in nature is
porcelain clay, or kaolin, which results from the decomposition of a rock
composed of feldspar and quartz, and it is almost always mixed with quartz.
The kaolin of China consists of 71·15 parts of silex, 15·86 of alumine, 1·92
of lime, and 6·73 of water;[1] but other porcelain clays differ materially, that
of Cornwall being composed, according to Boase, of nearly equal parts of
silica and alumine, with 1 per cent of magnesia.[2] Shale has also the
property, like clay, of becoming plastic in water: it is a more solid form of

clay, or argillaceous matter, condensed by pressure. It always divides into
laminæ more or less regular.
One general character of all argillaceous rocks is to give out a peculiar,
earthy odour when breathed upon, which is a test of the presence of
alumine, although it does not belong to pure alumine, but, apparently, to the
combination of that substance with oxide of iron.[3]
Calcareous Rocks.—This division comprehends those rocks which, like
chalk, are composed chiefly of lime and carbonic acid. Shells and corals are
also formed of the same elements, with the addition of animal matter. To
obtain pure lime it is necessary to calcine these calcareous substances, that
is to say, to expose them to heat of sufficient intensity to drive off the
carbonic acid, and other volatile matter. White chalk is sometimes pure
carbonate of lime; and this rock, although usually in a soft and earthy state,
is occasionally sufficiently solid to be used for building, and even passes
into a compact stone, or a stone of which the separate parts are so minute as
not to be distinguishable from each other by the naked eye.
Many limestones are made up entirely of minute fragments of shells and
coral, or of calcareous sand cemented together. These last might be called
“calcareous sandstones;” but that term is more properly applied to a rock in
which the grains are partly calcareous and partly siliceous, or to quartzose
sandstones, having a cement of carbonate of lime.
The variety of limestone called oolite is composed of numerous small
egg-like grains, resembling the roe of a fish, each of which has usually a
small fragment of sand as a nucleus, around which concentric layers of
calcareous matter have accumulated.
Any limestone which is sufficiently hard to take a fine polish is called
marble. Many of these are fossiliferous; but statuary marble, which is also
called saccharoid limestone, as having a texture resembling that of loaf-
sugar, is devoid of fossils, and is in many cases a member of the
metamorphic series.
Siliceous limestone is an intimate mixture of carbonate of lime and flint,
and is harder in proportion as the flinty matter predominates.
The presence of carbonate of lime in a rock may be ascertained by
applying to the surface a small drop of diluted sulphuric, nitric, or muriatic
acid, or strong vinegar; for the lime, having a greater chemical affinity for
any one of these acids than for the carbonic, unites immediately with them

to form new compounds, thereby becoming a sulphate, nitrate or muriate of
lime. The carbonic acid, when thus liberated from its union with the lime,
escapes in a gaseous form, and froths up or effervesces as it makes its way
in small bubbles through the drop of liquid. This effervescence is brisk or
feeble in proportion as the limestone is pure or impure, or, in other words,
according to the quantity of foreign matter mixed with the carbonate of
lime. Without the aid of this test, the most experienced eye cannot always
detect the presence of carbonate of lime in rocks.
The above-mentioned three classes of rocks, the siliceous, argillaceous,
and calcareous, pass continually into each other, and rarely occur in a
perfectly separate and pure form. Thus it is an exception to the general rule
to meet with a limestone as pure as ordinary white chalk, or with clay as
aluminous as that used in Cornwall for porcelain, or with sand so entirely
composed of siliceous grains as the white sand of Alum Bay, in the Isle of
Wight, employed in the manufacture of glass, or sandstone so pure as the
grit of Fontainebleau, used for pavement in France. More commonly we
find sand and clay, or clay and marl, intermixed in the same mass. When the
sand and clay are each in considerable quantity, the mixture is called loam.
If there is much calcareous matter in clay it is called marl; but this term has
unfortunately been used so vaguely, as often to be very ambiguous. It has
been applied to substances in which there is no lime; as, to that red loam
usually called red marl in certain parts of England. Agriculturists were in
the habit of calling any soil a marl which, like true marl, fell to pieces
readily on exposure to the air. Hence arose the confusion of using this name
for soils which, consisting of loam, were easily worked by the plough,
though devoid of lime.
Marl slate bears the same relation to marl which shale bears to clay,
being a calcareous shale. It is very abundant in some countries, as in the
Swiss Alps. Argillaceous or marly limestone is also of common occurrence.
There are few other kinds of rock which enter so largely into the
composition of sedimentary strata as to make it necessary to dwell here on
their characters. I may, however, mention two others—magnesian limestone
or dolomite, and gypsum. Magnesian limestone is composed of carbonate
of lime and carbonate of magnesia; the proportion of the latter amounting in
some cases to nearly one half. It effervesces much more slowly and feebly
with acids than common limestone. In England this rock is generally of a

yellowish colour; but it varies greatly in mineralogical character, passing
from an earthy state to a white compact stone of great hardness. Dolomite,
so common in many parts of Germany and France, is also a variety of
magnesian limestone, usually of a granular texture.
Gypsum is a rock composed of sulphuric acid, lime, and water. It is
usually a soft whitish-yellow rock, with a texture resembling that of loaf-
sugar, but sometimes it is entirely composed of lenticular crystals. It is
insoluble in acids, and does not effervesce like chalk and dolomite, because
it does not contain carbonic acid gas, or fixed air, the lime being already
combined with sulphuric acid, for which it has a stronger affinity than for
any other. Anhydrous gypsum is a rare variety, into which water does not
enter as a component part. Gypseous marl is a mixture of gypsum and marl.
Alabaster is a granular and compact variety of gypsum found in masses
large enough to be used in sculpture and architecture. It is sometimes a pure
snow-white substance, as that of Volterra in Tuscany, well known as being
carved for works of art in Florence and Leghorn. It is a softer stone than
marble, and more easily wrought.
Forms of Stratification.—A series of strata sometimes consists of one of
the above rocks, sometimes of two or more in alternating beds.
Thus, in the coal districts of England, for example, we often pass through
several beds of sandstone, some of finer, others of coarser grain, some
white, others of a dark colour, and below these, layers of shale and
sandstone or beds of shale, divisible into leaf-like laminæ, and containing
beautiful impressions of plants. Then again we meet with beds of pure and
impure coal, alternating with shales and sandstones, and underneath the
whole, perhaps, are calcareous strata, or beds of limestone, filled with
corals and marine shells, each bed distinguishable from another by certain
fossils, or by the abundance of particular species of shells or zoophytes.
This alternation of different kinds of rock produces the most distinct
stratification; and we often find beds of limestone and marl, conglomerate
and sandstone, sand and clay, recurring again and again, in nearly regular
order, throughout a series of many hundred strata. The causes which may
produce these phenomena are various, and have been fully discussed in my
treatise on the modern changes of the earth’s surface.[4] It is there seen that
rivers flowing into lakes and seas are charged with sediment, varying in
quantity, composition, colour, and grain according to the seasons; the waters

are sometimes flooded and rapid, at other periods low and feeble; different
tributaries, also, draining peculiar countries and soils, and therefore charged
with peculiar sediment, are swollen at distinct periods. It was also shown
that the waves of the sea and currents undermine the cliffs during wintry
storms, and sweep away the materials into the deep, after which a season of
tranquillity succeeds, when nothing but the finest mud is spread by the
movements of the ocean over the same submarine area.
It is not the object of the present work to give a description of these
operations, repeated as they are, year after year, and century after century;
but I may suggest an explanation of the manner in which some micaceous
sandstones have originated, namely, those in which we see innumerable thin
layers of mica dividing layers of fine quartzose sand. I observed the same
arrangement of materials in recent mud deposited in the estuary of Laroche
St. Bernard in Brittany, at the mouth of the Loire. The surrounding rocks are
of gneiss, which, by its waste, supplies the mud: when this dries at low
water, it is found to consist of brown laminated clay, divided by thin seams
of mica. The separation of the mica in this case, or in that of micaceous
sandstones, may be thus understood. If we take a handful of quartzose sand,
mixed with mica, and throw it into a clear running stream, we see the
materials immediately sorted by the water, the grains of quartz falling
almost directly to the bottom, while the plates of mica take a much longer
time to reach the bottom, and are carried farther down the stream. At the
first instant the water is turbid, but immediately after the flat surfaces of the
plates of mica are seen all alone, reflecting a silvery light, as they descend
slowly, to form a distinct micaceous lamina. The mica is the heavier mineral
of the two; but it remains a longer time suspended in the fluid, owing to its
greater extent of surface. It is easy, therefore, to perceive that where such
mud is acted upon by a river or tidal current, the thin plates of mica will be
carried farther, and not deposited in the same places as the grains of quartz;
and since the force and velocity of the stream varies from time to time,
layers of mica or of sand will be thrown down successively on the same
area.
Original Horizontality.—It is said generally that the upper and under
surfaces of strata, or the “planes of stratification,” are parallel. Although
this is not strictly true, they make an approach to parallelism, for the same
reason that sediment is usually deposited at first in nearly horizontal layers.
Such an arrangement can by no means be attributed to an original evenness

or horizontality in the bed of the sea: for it is ascertained that in those places
where no matter has been recently deposited, the bottom of the ocean is
often as uneven as that of the dry land, having in like manner its hills,
valleys, and ravines. Yet if the sea should go down, or be removed from
near the mouth of a large river where a delta has been forming, we should
see extensive plains of mud and sand laid dry, which, to the eye, would
appear perfectly level, although, in reality, they would slope gently from the
land towards the sea.
This tendency in newly-formed strata to assume a horizontal position
arises principally from the motion of the water, which forces along particles
of sand or mud at the bottom, and causes them to settle in hollows or
depressions where they are less exposed to the force of a current than when
they are resting on elevated points. The velocity of the current and the
motion of the superficial waves diminish from the surface downward, and
are least in those depressions where the water is deepest.

A good illustration of the principle here alluded to may be sometimes
seen in the neighbourhood of a volcano, when a section, whether natural or
artificial, has laid open to view a succession of various-coloured layers of
sand and ashes, which have fallen in showers upon uneven ground. Thus let
A B (Fig. 1) be two ridges, with an intervening valley. These original
inequalities of the surface have been gradually effaced by beds of sand and
ashes c, d, e, the surface at e being quite level. It will be seen that, although
the materials of the first layers have accommodated themselves in a great
degree to the shape of the ground A B, yet each bed is thickest at the
bottom. At first a great many particles would be carried by their own
gravity down the steep sides of A and B, and others would afterwards be
blown by the wind as they fell off the ridges, and would settle in the hollow,
which would thus become more and more effaced as the strata accumulated
from c to e. Now, water in motion can exert this levelling power on similar
materials more easily than air, for almost all stones lose in water more than
a third of the weight which they have in air, the specific gravity of rocks
being in general as 2½ when compared to that of water, which is estimated

at 1. But the buoyancy of sand or mud would be still greater in the sea, as
the density of salt-water exceeds that of fresh.

Yet, however uniform and horizontal may be the surface of new deposits
in general, there are still many disturbing causes, such as eddies in the
water, and currents moving first in one and then in another direction, which
frequently cause irregularities. We may sometimes follow a bed of
limestone, shale, or sandstone, for a distance of many hundred yards
continuously; but we generally find at length that each individual stratum
thins out, and allows the beds which were previously above and below it to
meet. If the materials are coarse, as in grits and conglomerates, the same
beds can rarely be traced many yards without varying in size, and often
coming to an end abruptly. (See Fig. 2.)

Diagonal or Cross Stratification.—There is also another phenomenon
of frequent occurrence. We find a series of larger strata, each of which is
composed of a number of minor layers placed obliquely to the general
planes of stratification. To this diagonal arrangement the name of “false or
cross bedding” has been given. Thus in the section (Fig. 3) we see seven or
eight large beds of loose sand, yellow and brown, and the lines a, b, c mark

some of the principal planes of stratification, which are nearly horizontal.
But the greater part of the subordinate laminæ do not conform to these
planes, but have often a steep slope, the inclination being sometimes
towards opposite points of the compass. When the sand is loose and
incoherent, as in the case here represented, the deviation from parallelism of
the slanting laminæ cannot possibly be accounted for by any rearrangement
of the particles acquired during the consolidation of the rock. In what
manner, then, can such irregularities be due to original deposition? We must
suppose that at the bottom of the sea, as well as in the beds of rivers, the
motions of waves, currents, and eddies often cause mud, sand, and gravel to
be thrown down in heaps on particular spots, instead of being spread out
uniformly over a wide area. Sometimes, when banks are thus formed,
currents may cut passages through them, just as a river forms its bed.

Suppose the bank A (Fig. 4) to be thus formed with a steep sloping side,
and, the water being in a tranquil state, the layer of sediment No. 1 is
thrown down upon it, conforming nearly to its surface. Afterwards the other
layers, 2, 3, 4, may be deposited in succession, so that the bank B C D is
formed. If the current then increases in velocity, it may cut away the upper
portion of this mass down to the dotted line e, and deposit the materials thus
removed farther on, so as to form the layers 5, 6, 7, 8. We have now the
bank B, C, D, E (Fig. 5), of which the surface is almost level, and on which
the nearly horizontal layers, 9, 10, 11, may then accumulate. It was shown
in Fig. 3 that the diagonal layers of successive strata may sometimes have
an opposite slope. This is well seen in some cliffs of loose sand on the
Suffolk coast. A portion of one of these is represented in Fig. 6, where the
layers, of which there are about six in the thickness of an inch, are

composed of quartzose grains. This arrangement may have been due to the
altered direction of the tides and currents in the same place.

The description above given of the slanting position of the minor layers
constituting a single stratum is in certain cases applicable on a much
grander scale to masses several hundred feet thick, and many miles in
extent. A fine example may be seen at the base of the Maritime Alps near
Nice. The mountains here terminate abruptly in the sea, so that a depth of
one hundred fathoms is often found within a stone’s throw of the beach, and
sometimes a depth of 3000 feet within half a mile. But at certain points,
strata of sand, marl, or conglomerate intervene between the shore and the
mountains, as in the section (Fig. 7), where a vast succession of slanting
beds of gravel and sand may be traced from the sea to Monte Calvo, a
distance of no less than nine miles in a straight line. The dip of these beds is
remarkably uniform, being always southward or towards the Mediterranean,
at an angle of about 25°. They are exposed to view in nearly vertical
precipices, varying from 200 to 600 feet in height, which bound the valley
through which the river Magnan flows. Although, in a general view, the
strata appear to be parallel and uniform, they are nevertheless found, when
examined closely, to be wedge-shaped, and to thin out when followed for a
few hundred feet or yards, so that we may suppose them to have been
thrown down originally upon the side of a steep bank where a river or

Alpine torrent discharged itself into a deep and tranquil sea, and formed a
delta, which advanced gradually from the base of Monte Calvo to a distance
of nine miles from the original shore. If subsequently this part of the Alps
and bed of the sea were raised 700 feet, the delta may have emerged, a deep
channel may then have been cut through it by the river, and the coast may at
the same time have acquired its present configuration.
It is well known that the torrents and streams which now descend from
the Alpine declivities to the shore, bring down annually, when the snow
melts, vast quantities of shingle and sand, and then, as they subside, fine
mud, while in summer they are nearly or entirely dry; so that it may be
safely assumed that deposits like those of the valley of the Magnan,
consisting of coarse gravel alternating with fine sediment, are still in
progress at many points, as, for instance, at the mouth of the Var. They must
advance upon the Mediterranean in the form of great shoals terminating in a
steep talus; such being the original mode of accumulation of all coarse
materials conveyed into deep water, especially where they are composed in
great part of pebbles, which cannot be transported to indefinite distances by
currents of moderate velocity. By inattention to facts and inferences of this
kind, a very exaggerated estimate has sometimes been made of the
supposed depth of the ancient ocean. There can be no doubt, for example,
that the strata a, Fig. 7, or those nearest to Monte Calvo, are older than
those indicated by b, and these again were formed before c; but the vertical
depth of gravel and sand in any one place cannot be proved to amount even
to 1000 feet, although it may perhaps be much greater, yet probably never
exceeding at any point 3000 or 4000 feet. But were we to assume that all
the strata were once horizontal, and that their present dip or inclination was
due to subsequent movements, we should then be forced to conclude that a
sea several miles deep had been filled up with alternate layers of mud and
pebbles thrown down one upon another.
In the locality now under consideration, situated a few miles to the west
of Nice, there are many geological data, the details of which cannot be
given in this place, all leading to the opinion that, when the deposit of the
Magnan was formed, the shape and outline of the Alpine declivities and the
shore greatly resembled what we now behold at many points in the
neighbourhood. That the beds a, b, c, d are of comparatively modern date is
proved by this fact, that in seams of loamy marl intervening between the

pebbly beds are fossil shells, half of which belong to species now living in
the Mediterranean.

Ripple-mark.—The ripple-mark, so common on the surface of
sandstones of all ages (see Fig. 8), and which is so often seen on the sea-
shore at low tide, seems to originate in the drifting of materials along the
bottom of the water, in a manner very similar to that which may explain the
inclined layers above described. This ripple is not entirely confined to the
beach between high and low water mark, but is also produced on sands
which are constantly covered by water. Similar undulating ridges and
furrows may also be sometimes seen on the surface of drift snow and blown
sand.
The ripple-mark is usually an indication of a sea-beach, or of water from
six to ten feet deep, for the agitation caused by waves even during storms
extends to a very slight depth. To this rule, however, there are some
exceptions, and recent ripple-marks have been observed at the depth of 60
or 70 feet. It has also been ascertained that currents or large bodies of water
in motion may disturb mud and sand at the depth of 300 or even 450 feet.[5]
Beach ripple, however, may usually be distinguished from current ripple by
frequent changes in its direction. In a slab of sandstone, not more than an
inch thick, the furrows or ridges of an ancient ripple may often be seen in
several successive laminæ to run towards different points of the compass.
[1] W. Phillips, Mineralogy, p.33.

[2] Phil. Mag., vol. x, 1837.

[3] See W. Phillips’s Mineralogy, “Alumine.”

[4] Consult Index to Principles of Geology, “Stratification,” “Currents,”
“Deltas,” “Water,” etc.

[5] Darwin, Volcanic Islands, p. 134.

CHAPTER III.
ARRANGEMENT OF FOSSILS IN STRATA.—
FRESH-WATER AND MARINE FOSSILS.

Successive Deposition indicated by Fossils. — Limestones
formed of Corals and Shells. — Proofs of gradual Increase
of Strata derived from Fossils. — Serpula attached to
Spatangus. — Wood bored by Teredina. — Tripoli formed of
Infusoria. — Chalk derived principally from Organic
Bodies. — Distinction of Fresh-water from Marine
Formations. — Genera of Fresh-water and Land Shells. —
Rules for recognising Marine Testacea. — Gyrogonite and
Chara. — Fresh-water Fishes. — Alternation of Marine and
Fresh-water Deposits. — Lym-Fiord.

Having in the last chapter considered the forms of stratification so far as
they are determined by the arrangement of inorganic matter, we may now
turn our attention to the manner in which organic remains are distributed
through stratified deposits. We should often be unable to detect any signs of
stratification or of successive deposition, if particular kinds of fossils did
not occur here and there at certain depths in the mass. At one level, for
example, univalve shells of some one or more species predominate; at
another, bivalve shells; and at a third, corals; while in some formations we
find layers of vegetable matter, commonly derived from land plants,
separating strata.
It may appear inconceivable to a beginner how mountains, several
thousand feet thick, can have become full of fossils from top to bottom; but
the difficulty is removed, when he reflects on the origin of stratification, as
explained in the last chapter, and allows sufficient time for the

accumulation of sediment. He must never lose sight of the fact that, during
the process of deposition, each separate layer was once the uppermost, and
immediately in contact with the water in which aquatic animals lived. Each
stratum, in fact, however far it may now lie beneath the surface, was once in
the state of shingle, or loose sand or soft mud at the bottom of the sea, in
which shells and other bodies easily became enveloped.
Rate of Deposition indicated by Fossils.—By attending to the nature of
these remains, we are often enabled to determine whether the deposition
was slow or rapid, whether it took place in a deep or shallow sea, near the
shore or far from land, and whether the water was salt, brackish, or fresh.
Some limestones consist almost exclusively of corals, and in many cases it
is evident that the present position of each fossil zoophyte has been
determined by the manner in which it grew originally. The axis of the coral,
for example, if its natural growth is erect, still remains at right angles to the
plane of stratification. If the stratum be now horizontal, the round spherical
heads of certain species continue uppermost, and their points of attachment
are directed downward. This arrangement is sometimes repeated throughout
a great succession of strata. From what we know of the growth of similar
zoophytes in modern reefs, we infer that the rate of increase was extremely
slow, and some of the fossils must have flourished for ages like forest-trees,
before they attained so large a size. During these ages, the water must have
been clear and transparent, for such corals cannot live in turbid water.

In like manner, when we see thousands of full-grown shells dispersed
everywhere throughout a long series of strata, we cannot doubt that time
was required for the multiplication of successive generations; and the
evidence of slow accumulation is rendered more striking from the proofs,
so often discovered, of fossil bodies having lain for a time on the floor of
the ocean after death before they were imbedded in sediment. Nothing, for
example, is more common than to see fossil oysters in clay, with Serpulæ,
or barnacles (acorn-shells), or corals, and other creatures, attached to the
inside of the valves, so that the mollusk was certainly not buried in
argillaceous mud the moment it died. There must have been an interval
during which it was still surrounded with clear water, when the creatures
whose remains now adhere to it grew from an embryonic to a mature state.
Attached shells which are merely external, like some of the Serpulæ (a) in
Fig. 9, may often have grown upon an oyster or other shell while the animal
within was still living; but if they are found on the inside, it could only
happen after the death of the inhabitant of the shell which affords the
support. Thus, in Fig. 9, it will be seen that two Serpulæ have grown on the
interior, one of them exactly on the place where the adductor muscle of the
Gryphæa (a kind of oyster) was fixed.

Some fossil shells, even if simply attached to the outside of others, bear
full testimony to the conclusion above alluded to, namely, that an interval
elapsed between the death of the creature to whose shell they adhere, and
the burial of the same in mud or sand. The sea-urchins, or Echini, so
abundant in white chalk, afford a good illustration. It is well known that
these animals, when living, are invariably covered with spines supported by
rows of tubercles. These last are only seen after the death of the sea-urchin,
when the spines have dropped off. In Fig. 11 a living species of Spatangus,
common on our coast, is represented with one half of its shell stripped of
the spines. In Fig. 10 a fossil of a similar and allied genus from the white
chalk of England shows the naked surface which the individuals of this
family exhibit when denuded of their bristles. The full-grown Serpula,
therefore, which now adheres externally, could not have begun to grow till
the Micraster had died, and the spines became detached.

Now the series of events here attested by a single fossil may be carried a
step farther. Thus, for example, we often meet with a sea-urchin
(Ananchytes) in the chalk (see Fig. 12) which has fixed to it the lower valve
of a Crania, a genus of bivalve mollusca. The upper valve (b, Fig. 12) is
almost invariably wanting, though occasionally found in a perfect state of
preservation in white chalk at some distance. In this case, we see clearly
that the sea-urchin first lived from youth to age, then died and lost its
spines, which were carried away. Then the young Crania adhered to the
bared shell, grew and perished in its turn; after which the upper valve was
separated from the lower before the Ananchytes became enveloped in
chalky mud.

It may be well to mention one more illustration of the manner in which
single fossils may sometimes throw light on a former state of things, both in
the bed of the ocean and on some adjoining land. We meet with many
fragments of wood bored by ship-worms at various depths in the clay on
which London is built. Entire branches and stems of trees, several feet in
length, are sometimes found drilled all over by the holes of these borers, the
tubes and shells of the mollusk still remaining in the cylindrical hollows. In
Fig. 14, e, a representation is given of a piece of recent wood pierced by the
Teredo navalis, or common ship-worm, which destroys wooden piles and
ships. When the cylindrical tube d has been extracted from the wood, the
valves are seen at the larger or anterior extremity, as shown at c. In like
manner, a piece of fossil wood (a, Fig. 13) has been perforated by a kindred
but extinct genus, the Teredina of Lamarck. The calcareous tube of this
mollusk was united and, as it were, soldered on to the valves of the shell
(b), which therefore cannot be detached from the tube, like the valves of the
recent Teredo. The wood in this fossil specimen is now converted into a
stony mass, a mixture of clay and lime; but it must once have been buoyant
and floating in the sea, when the Teredinæ lived upon, and perforated it.
Again, before the infant colony settled upon the drift wood, part of a tree
must have been floated down to the sea by a river, uprooted, perhaps, by a
flood, or torn off and cast into the waves by the wind: and thus our thoughts
are carried back to a prior period, when the tree grew for years on dry land,
enjoying a fit soil and climate.
Strata of Organic Origin.—It has been already remarked that there are
rocks in the interior of continents, at various depths in the earth, and at great
heights above the sea, almost entirely made up of the remains of zoophytes
and testacea. Such masses may be compared to modern oyster-beds and
coral-reefs; and, like them, the rate of increase must have been extremely
gradual. But there are a variety of stone deposits in the earth’s crust, now
proved to have been derived from plants and animals of which the organic
origin was not suspected until of late years, even by naturalists. Great
surprise was therefore created some years since by the discovery of
Professor Ehrenberg, of Berlin, that a certain kind of siliceous stone, called
tripoli, was entirely composed of millions of the remains of organic beings,
which were formerly referred to microscopic Infusoria, but which are now
admitted to be plants. They abound in rivulets, lakes, and ponds in England
and other countries, and are termed Diatomaceæ by those naturalists who

believe in their vegetable origin. The subject alluded to has long been well-
known in the arts, under the name of infusorial earth or mountain meal, and
is used in the form of powder for polishing stones and metals. It has been
procured, among other places, from the mud of a lake at Dolgelly, in North
Wales, and from Bilin, in Bohemia, in which latter place a single stratum,
extending over a wide area, is no less than fourteen feet thick. This stone,
when examined with a powerful microscope, is found to consist of the
siliceous plates or frustules of the above-figured Diatomaceæ, united
together without any visible cement. It is difficult to convey an idea of their
extreme minuteness; but Ehrenberg estimates that in the Bilin tripoli there
are 41,000 millions of individuals of the Gaillonella distans (see Fig. 16) in
every cubic inch (which weighs about 220 grains), or about 187 millions in
a single grain. At every stroke, therefore, that we make with this polishing
powder, several millions, perhaps tens of millions, of perfect fossils are
crushed to atoms.

A well-known substance, called bog-iron ore, often met with in peat-
mosses, has often been shown by Ehrenberg to consist of innumerable
articulated threads, of a yellow ochre colour, composed of silica,
argillaceous matter, and peroxide of iron. These threads are the cases of a
minute microscopic body, called Gaillonella ferruginea (Fig. 15),
associated with the siliceous frustules of other fresh-water algæ. Layers of
this iron ore occurring in Scotch peat bogs are often called “the pan,” and
are sometimes of economical value.
It is clear much time must have been required for the accumulation of
strata to which countless generations of Diatomaceæ have contributed their

remains; and these discoveries lead us naturally to suspect that other
deposits, of which the materials have been supposed to be inorganic, may in
reality be composed chiefly of microscopic organic bodies. That this is the
case with the white chalk, has often been imagined, and is now proved to be
the fact. It has, moreover, been lately discovered that the chambers into
which these Foraminifera are divided are actually often filled with
thousands of well-preserved organic bodies, which abound in every minute
grain of chalk, and are especially apparent in the white coating of flints,
often accompanied by innumerable needle-shaped spiculæ of sponges (see
Chapter XVII).
“The dust we tread upon was once alive!”—BYRON.

How faint an idea does this exclamation of the poet convey of the real
wonders of nature! for here we discover proofs that the calcareous and
siliceous dust of which hills are composed has not only been once alive, but
almost every particle, albeit invisible to the naked eye, still retains the
organic structure which, at periods of time incalculably remote, was
impressed upon it by the powers of life.
Fresh-water and Marine Fossils.—Strata, whether deposited in salt or
fresh water, have the same forms; but the imbedded fossils are very
different in the two cases, because the aquatic animals which frequent lakes
and rivers are distinct from those inhabiting the sea. In the northern part of
the Isle of Wight formations of marl and limestone, more than 50 feet thick
occur, in which the shells are of extinct species. Yet we recognise their
fresh-water origin, because they are of the same genera as those now
abounding in ponds, lakes, and rivers, either in our own country or in
warmer latitudes.
In many parts of France—in Auvergne, for example—strata occur of
limestone, marl, and sandstone hundreds of feet thick, which contain
exclusively fresh-water and land shells, together with the remains of
terrestrial quadrupeds. The number of land-shells scattered through some of
these fresh-water deposits is exceedingly great; and there are districts in
Germany where the rocks scarcely contain any other fossils except snail-
shells (helices); as, for instance, the limestone on the left bank of the Rhine,
between Mayence and Worms, at Oppenheim, Findheim, Budenheim, and
other places. In order to account for this phenomenon, the geologist has
only to examine the small deltas of torrents which enter the Swiss lakes

when the waters are low, such as the newly-formed plain where the Kander
enters the Lake of Thun. He there sees sand and mud strewn over with
innumerable dead land-shells, which have been brought down from the
valleys in the Alps in the preceding spring, during the melting of the snows.
Again, if we search the sands on the borders of the Rhine, in the lower part
of its course, we find countless land-shells mixed with others of species
belonging to lakes, stagnant pools, and marshes. These individuals have
been washed away from the alluvial plains of the great river and its
tributaries, some from mountainous regions, others from the low country.
Although fresh-water formations are often of great thickness, yet they are
usually very limited in area when compared to marine deposits, just as lakes
and estuaries are of small dimensions in comparison with seas.
The absence of many fossil forms usually met with in marine strata,
affords a useful negative indication of the fresh-water origin of a formation.
For example, there are no sea-urchins, no corals, no chambered shells, such
as the nautilus, nor microscopic Foraminifera in lacustrine or fluviatile
deposits. In distinguishing the latter from formations accumulated in the
sea, we are chiefly guided by the forms of the mollusca. In a fresh-water
deposit, the number of individual shells is often as great as in a marine
stratum, if not greater; but there is a smaller variety of species and genera.
This might be anticipated from the fact that the genera and species of recent
fresh-water and land shells are few when contrasted with the marine. Thus,
the genera of true mollusca according to Woodward’s system, excluding
those altogether extinct and those without shells, amount to 446 in number,
of which the terrestrial and fresh-water genera scarcely form more than a
fifth.[1]

Almost all bivalve shells, or those of acephalous mollusca, are marine,
about sixteen only out of 140 genera being fresh-water. Among these last,
the four most common forms, both recent and fossil, are Cyclas, Cyrena,
Unio, and Anodonta (see Figures); the two first and two last of which are so
nearly allied as to pass into each other.

Lamarck divided the bivalve mollusca into the Dimyary, or those having
two large muscular impressions in each valve, as a b in the Cyclas, Fig. 18,
and Unio, Fig. 22, and the Monomyary, such as the oyster and scallop, in
which there is only one of these impressions, as is seen in Fig. 23. Now, as
none of these last, or the unimuscular bivalves, are fresh-water,[2] we may at
once presume a deposit containing any of them to be marine.

The univalve shells most characteristic of fresh-water deposits are,
Planorbis, Limnæa, and Paludina. (See Figures.) But to these are
occasionally added Physa, Succinea, Ancylus, Valvata, Melanopsis,
Melania, Potamides, and Neritina (see Figures), the four last being usually
found in estuaries.

Some naturalists include Neritina (Fig. 35) and the marine Nerita (Fig.
36) in the same genus, it being scarcely possible to distinguish the two by
good generic characters. But, as a general rule, the fluviatile species are
smaller, smoother, and more globular than the marine; and they have never,
like the Neritæ, the inner margin of the outer lip toothed or crenulated. (See
Fig. 36.)
The Potamides inhabit the mouths of rivers in warm latitudes, and are
distinguishable from the marine Cerithia by their orbicular and multispiral
opercula. The genus Auricula (Fig. 31) is amphibious, frequenting swamps
and marshes within the influence of the tide.
The terrestrial shells are all univalves. The most important genera among
these, both in a recent and fossil state, are Helix (Fig. 38), Cyclostoma (Fig.
39), Pupa (Fig. 40), Clausilia (Fig. 41), Bulimus (Fig. 42), Glandina and
Achatina.

Ampullaria (Fig. 43) is another genus of shells inhabiting rivers and
ponds in hot countries. Many fossil species formerly referred to this genus,
and which have been met with chiefly in marine formations, are now
considered by conchologists to belong to Natica and other marine genera.

All univalve shells of land and fresh-water species, with the exception of
Melanopsis (Fig. 34), and Achatina, which has a slight indentation, have
entire mouths; and this circumstance may often serve as a convenient rule
for distinguishing fresh-water from marine strata; since, if any univalves
occur of which the mouths are not entire, we may presume that the
formation is marine. The aperture is said to be entire in such shells as the
fresh-water Ampullaria and the land-shells (Figs 38-42), when its outline is
not interrupted by an indentation or notch, such as that seen at b in
Ancillaria (Fig. 45); or is not prolonged into a canal, as that seen at a in
Pleurotoma (Fig. 44).

The mouths of a large proportion of the marine univalves have these
notches or canals, and almost all species are carnivorous; whereas nearly all
testacea having entire mouths are plant-eaters, whether the species be
marine, fresh-water, or terrestrial.
There is, however, one genus which affords an occasional exception to
one of the above rules. The Potamides (Fig. 37), a subgenus of Cerithium,
although provided with a short canal, comprises some species which inhabit
salt, others brackish, and others fresh-water, and they are said to be all
plant-eaters.

Among the fossils very common in fresh-water deposits are the shells of
Cypris, a minute bivalve crustaceous animal.[3] Many minute living species
of this genus swarm in lakes and stagnant pools in Great Britain; but their
shells are not, if considered separately, conclusive as to the fresh-water
origin of a deposit, because the majority of species in another kindred genus
of the same order, the Cytherina of Lamarck, inhabit salt-water; and,
although the animal differs slightly, the shell is scarcely distinguishable
from that of the Cypris.
Fresh-water Fossil Plants.—The seed-vessels and stems of Chara, a
genus of aquatic plants, are very frequent in fresh-water strata. These seed-
vessels were called, before their true nature was known, gyrogonites, and
were supposed to be foraminiferous shells. (See Fig. 46, a.)
The Charæ inhabit the bottom of lakes and ponds, and flourish mostly
where the water is charged with carbonate of lime. Their seed-vessels are
covered with a very tough integument, capable of resisting decomposition;
to which circumstance we may attribute their abundance in a fossil state.
The annexed figure (Fig. 47) represents a branch of one of many new
species found by Professor Amici in the lakes of Northern Italy. The seed-
vessel in this plant is more globular than in the British Charæ,) and
therefore more nearly resembles in form the extinct fossil species found in
England, France, and other countries. The stems, as well as the seed-
vessels, of these plants occur both in modern shell-marl and in ancient
fresh-water formations. They are generally composed of a large central tube
surrounded by smaller ones; the whole stem being divided at certain
intervals by transverse partitions or joints. (See b, Fig. 46.)

It is not uncommon to meet with layers of vegetable matter, impressions
of leaves, and branches of trees, in strata containing fresh-water shells; and
we also find occasionally the teeth and bones of land quadrupeds, of species
now unknown. The manner in which such remains are occasionally carried
by rivers into lakes, especially during floods, has been fully treated of in the
“Principles of Geology.”
Fresh-water and Marine Fish.—The remains of fish are occasionally
useful in determining the fresh-water origin of strata. Certain genera, such
as carp, perch, pike, and loach (Cyprinus, Perca, Esox, and Cobitis), as also
Lebias, being peculiar to fresh-water. Other genera contain some fresh-
water and some marine species, as Cottus, Mugil, and Anguilla, or eel. The
rest are either common to rivers and the sea, as the salmon; or are
exclusively characteristic of salt-water. The above observations respecting
fossil fishes are applicable only to the more modern or tertiary deposits; for
in the more ancient rocks the forms depart so widely from those of existing
fishes, that it is very difficult, at least in the present state of science, to
derive any positive information from ichthyolites respecting the element in
which strata were deposited.
The alternation of marine and fresh-water formations, both on a small
and large scale, are facts well ascertained in geology. When it occurs on a
small scale, it may have arisen from the alternate occupation of certain
spaces by river-water and the sea; for in the flood season the river forces
back the ocean and freshens it over a large area, depositing at the same time
its sediment; after which the salt-water again returns, and, on resuming its
former place, brings with it sand, mud, and marine shells.
There are also lagoons at the mouth of many rivers, as the Nile and
Mississippi, which are divided off by bars of sand from the sea, and which
are filled with salt and fresh water by turns. They often communicate
exclusively with the river for months, years, or even centuries; and then a
breach being made in the bar of sand, they are for long periods filled with
salt-water.
Lym-Fiord.—The Lym-Fiord in Jutland offers an excellent illustration of
analogous changes; for, in the course of the last thousand years, the western
extremity of this long frith, which is 120 miles in length, including its
windings, has been four times fresh and four times salt, a bar of sand
between it and the ocean having been often formed and removed. The last

irruption of salt water happened in 1824, when the North Sea entered,
killing all the fresh-water shells, fish, and plants; and from that time to the
present, the sea-weed Fucus vesiculosus, together with oysters and other
marine mollusca, have succeeded the Cyclas, Lymnæa, Paludina, and
Charæ.[4]
But changes like these in the Lym-Fiord, and those before mentioned as
occurring at the mouths of great rivers, will only account for some cases of
marine deposits of partial extent resting on fresh-water strata. When we
find, as in the south-east of England (Chapter XVIII), a great series of
fresh-water beds, 1000 feet in thickness, resting upon marine formations
and again covered by other rocks, such as the Cretaceous, more than 1000
feet thick, and of deep-sea origin, we shall find it necessary to seek for a
different explanation of the phenomena.
[1] See Woodward’s Manual of Mollusca, 1856.

[2] The fresh-water Mulleria, when young, forms a single exception to the rule,
as it then has two muscular impressions, but it has only one in the adult state.

[3] For figures of fossil species of Purbeck, see Chapter XIX

[4] See Principles, Index, “Lym-Fiord.”

CHAPTER IV.
CONSOLIDATION OF STRATA AND
PETRIFACTION OF FOSSILS.

Chemical and Mechanical Deposits. — Cementing together
of Particles. — Hardening by Exposure to Air. —
Concretionary Nodules. — Consolidating Effects of
Pressure. — Mineralization of Organic Remains. —
Impressions and Casts: how formed. — Fossil Wood. —
Goppert’s Experiments. — Precipitation of Stony Matter
most rapid where Putrefaction is going on. — Sources of
Lime and Silex in Solution.

Having spoken in the preceding chapters of the characters of sedimentary
formations, both as dependent on the deposition of inorganic matter and the
distribution of fossils, I may next treat of the consolidation of stratified
rocks, and the petrifaction of imbedded organic remains.
Chemical and Mechanical Deposits.— A distinction has been made by
geologists between deposits of a mechanical, and those of a chemical,
origin. By the name mechanical are designated beds of mud, sand, or
pebbles produced by the action of running water, also accumulations of
stones and scoriæ thrown out by a volcano, which have fallen into their
present place by the force of gravitation. But the matter which forms a
chemical deposit has not been mechanically suspended in water, but in a
state of solution until separated by chemical action. In this manner
carbonate of lime is occasionally precipitated upon the bottom of lakes in a
solid form, as may be well seen in many parts of Italy, where mineral
springs abound, and where the calcareous stone, called travertin, is
deposited. In these springs the lime is usually held in solution by an excess

of carbonic acid, or by heat if it be a hot spring, until the water, on issuing
from the earth, cools or loses part of its acid. The calcareous matter then
falls down in a solid state, incrusting shells, fragments of wood and leaves,
and binding them together.
That similar travertin is formed at some points in the bed of the sea
where calcareous springs issue cannot be doubted, but as a general rule the
quantity of lime, according to Bischoff, spread through the waters of the
ocean is very small, the free carbonic acid gas in the same waters being five
times as much as is necessary to keep the lime in a fluid state. Carbonate of
lime, therefore, can rarely be precipitated at the bottom of the sea by
chemical action alone, but must be produced by vital agency as in the case
of coral reefs.
In such reefs, large masses of limestone are formed by the stony
skeletons of zoophytes; and these, together with shells, become cemented
together by carbonate of lime, part of which is probably furnished to the
sea-water by the decomposition of dead corals. Even shells, of which the
animals are still living on these reefs, are very commonly found to be
incrusted over with a hard coating of limestone.
If sand and pebbles are carried by a river into the sea, and these are
bound together immediately by carbonate of lime, the deposit may be
described as of a mixed origin, partly chemical, and partly mechanical.
Now, the remarks already made in Chapter II, on the original
horizontality of strata are strictly applicable to mechanical deposits, and
only partially to those of a mixed nature. Such as are purely chemical may
be formed on a very steep slope, or may even incrust the vertical walls of a
fissure, and be of equal thickness throughout; but such deposits are of small
extent, and for the most part confined to vein-stones.
Consolidation of Strata.—It is chiefly in the case of calcareous rocks
that solidification takes place at the time of deposition. But there are many
deposits in which a cementing process comes into operation long
afterwards. We may sometimes observe, where the water of ferruginous or
calcareous springs has flowed through a bed of sand or gravel, that iron or
carbonate of lime has been deposited in the interstices between the grains or
pebbles, so that in certain places the whole has been bound together into a
stone, the same set of strata remaining in other parts loose and incoherent.

Proofs of a similar cementing action are seen in a rock at Kelloway, in
Wiltshire. A peculiar band of sandy strata belonging to the group called
Oolite by geologists may be traced through several counties, the sand being
for the most part loose and unconsolidated, but becoming stony near
Kelloway. In this district there are numerous fossil shells which have
decomposed, having for the most part left only their casts. The calcareous
matter hence derived has evidently served, at some former period, as a
cement to the siliceous grains of sand, and thus a solid sandstone has been
produced. If we take fragments of many other argillaceous grits, retaining
the casts of shells, and plunge them into dilute muriatic or other acid, we
see them immediately changed into common sand and mud; the cement of
lime, derived from the shells, having been dissolved by the acid.
Traces of impressions and casts are often extremely faint. In some loose
sands of recent date we meet with shells in so advanced a stage of
decomposition as to crumble into powder when touched. It is clear that
water percolating such strata may soon remove the calcareous matter of the
shell; and unless circumstances cause the carbonate of lime to be again
deposited, the grains of sand will not be cemented together; in which case
no memorial of the fossil will remain.
In what manner silex and carbonate of lime may become widely diffused
in small quantities through the waters which permeate the earth’s crust will
be spoken of presently, when the petrifaction of fossil bodies is considered;
but I may remark here that such waters are always passing in the case of
thermal springs from hotter to colder parts of the interior of the earth; and,
as often as the temperature of the solvent is lowered, mineral matter has a
tendency to separate from it and solidify. Thus a stony cement is often
supplied to sand, pebbles, or any fragmentary mixture. In some
conglomerates, like the pudding-stone of Hertfordshire (a Lower Eocene
deposit), pebbles of flint and grains of sand are united by a siliceous cement
so firmly, that if a block be fractured, the rent passes as readily through the
pebbles as through the cement.
It is probable that many strata became solid at the time when they
emerged from the waters in which they were deposited, and when they first
formed a part of the dry land. A well-known fact seems to confirm this idea:
by far the greater number of the stones used for building and road-making
are much softer when first taken from the quarry than after they have been

long exposed to the air; and these, when once dried, may afterwards be
immersed for any length of time in water without becoming soft again.
Hence it is found desirable to shape the stones which are to be used in
architecture while they are yet soft and wet, and while they contain their
“quarry-water,” as it is called; also to break up stone intended for roads
when soft, and then leave it to dry in the air for months that it may harden.
Such induration may perhaps be accounted for by supposing the water,
which penetrates the minutest pores of rocks, to deposit, on evaporation,
carbonate of lime, iron, silex, and other minerals previously held in
solution, and thereby to fill up the pores partially. These particles, on
crystallising, would not only be themselves deprived of freedom of motion,
but would also bind together other portions of the rock which before were
loosely aggregated. On the same principle wet sand and mud become as
hard as stone when frozen; because one ingredient of the mass, namely, the
water, has crystallised, so as to hold firmly together all the separate particles
of which the loose mud and sand were composed.
Dr. MacCulloch mentions a sandstone in Skye, which may be moulded
like dough when first found; and some simple minerals, which are rigid and
as hard as glass in our cabinets, are often flexible and soft in their native
beds: this is the case with asbestos, sahlite, tremolite, and chalcedony, and it
is reported also to happen in the case of the beryl.[1]
The marl recently deposited at the bottom of Lake Superior, in North
America, is soft, and often filled with fresh-water shells; but if a piece be
taken up and dried, it becomes so hard that it can only be broken by a smart
blow of the hammer. If the lake, therefore, was drained, such a deposit
would be found to consist of strata of marlstone, like that observed in many
ancient European formations, and, like them, containing fresh-water shells.

Concretionary Structure.—It is probable that some of the
heterogeneous materials which rivers transport to the sea may at once set
under water, like the artificial mixture called pozzolana, which consists of
fine volcanic sand charged with about twenty per cent of oxide of iron, and
the addition of a small quantity of lime. This substance hardens, and

becomes a solid stone in water, and was used by the Romans in constructing
the foundations of buildings in the sea. Consolidation in such cases is
brought about by the action of chemical affinity on finely comminuted
matter previously suspended in water. After deposition similar particles
seem often to exert a mutual attraction on each other, and congregate
together in particular spots, forming lumps, nodules, and concretions. Thus
in many argillaceous deposits there are calcareous balls, or spherical
concretions, ranged in layers parallel to the general stratification; an
arrangement which took place after the shale or marl had been thrown down
in successive laminæ; for these laminæ are often traceable through the
concretions, remaining parallel to those of the surrounding unconsolidated
rock. (See Fig. 48.) Such nodules of limestone have often a shell or other
foreign body in the centre.
Among the most remarkable examples of concretionary structure are
those described by Professor Sedgwick as abounding in the magnesian
limestone of the north of England. The spherical balls are of various sizes,
from that of a pea to a diameter of several feet, and they have both a
concentric and radiated structure, while at the same time the laminæ of
original deposition pass uninterruptedly through them. In some cliffs this
limestone resembles a great irregular pile of cannon-balls. Some of the
globular masses have their centre in one stratum, while a portion of their
exterior passes through to the stratum above or below. Thus the larger
spheroid in the section (Fig. 49) passes from the stratum b upward into a. In
this instance we must suppose the deposition of a series of minor layers,
first forming the stratum b, and afterwards the incumbent stratum a; then a
movement of the particles took place, and the carbonates of lime and
magnesia separated from the more impure and mixed matter forming the
still unconsolidated parts of the stratum. Crystallisation, beginning at the
centre, must have gone on forming concentric coats around the original
nucleus without interfering with the laminated structure of the rock.

When the particles of rocks have been thus rearranged by chemical
forces, it is sometimes difficult or impossible to ascertain whether certain
lines of division are due to original deposition or to the subsequent
aggregation of several particles. Thus suppose three strata of grit, A, B, C,
are charged unequally with calcareous matter, and that B is the most
calcareous. If consolidation takes place in B, the concretionary action may
spread upward into a part of A, where the carbonate of lime is more
abundant than in the rest; so that a mass, d e f, forming a portion of the
superior stratum, becomes united with B into one solid mass of stone. The
original line of division, d e, being thus effaced, the line d f would generally
be considered as the surface of the bed B, though not strictly a true plane of
stratification.
Pressure and Heat.—When sand and mud sink to the bottom of a deep
sea, the particles are not pressed down by the enormous weight of the
incumbent ocean; for the water, which becomes mingled with the sand and
mud, resists pressure with a force equal to that of the column of fluid above.
The same happens in regard to organic remains which are filled with water
under great pressure as they sink, otherwise they would be immediately
crushed to pieces and flattened. Nevertheless, if the materials of a stratum
remain in a yielding state, and do not set or solidify, they will be gradually
squeezed down by the weight of other materials successively heaped upon
them, just as soft clay or loose sand on which a house is built may give way.
By such downward pressure particles of clay, sand, and marl may become
packed into a smaller space, and be made to cohere together permanently.
Analogous effects of condensation may arise when the solid parts of the
earth’s crust are forced in various directions by those mechanical
movements hereafter to be described, by which strata have been bent,

broken, and raised above the level of the sea. Rocks of more yielding
materials must often have been forced against others previously
consolidated, and may thus by compression have acquired a new structure.
A recent discovery may help us to comprehend how fine sediment derived
from the detritus of rocks may be solidified by mere pressure. The graphite
or “black lead” of commerce having become very scarce, Mr. Brockedon
contrived a method by which the dust of the purer portions of the mineral
found in Borrowdale might be recomposed into a mass as dense and
compact as native graphite. The powder of graphite is first carefully
prepared and freed from air, and placed under a powerful press on a strong
steel die, with air-tight fittings. It is then struck several blows, each of a
power of 1000 tons; after which operation the powder is so perfectly
solidified that it can be cut for pencils, and exhibits when broken the same
texture as native graphite.
But the action of heat at various depths in the earth is probably the most
powerful of all causes in hardening sedimentary strata. To this subject I
shall refer again when treating of the metamorphic rocks, and of the slaty
and jointed structure.
Mineralisation of Organic Remains.—The changes which fossil
organic bodies have undergone since they were first imbedded in rocks,
throw much light on the consolidation of strata. Fossil shells in some
modern deposits have been scarcely altered in the course of centuries,
having simply lost a part of their animal matter. But in other cases the shell
has disappeared, and left an impression only of its exterior, or, secondly, a
cast of its interior form, or, thirdly, a cast of the shell itself, the original
matter of which has been removed. These different forms of fossilisation
may easily be understood if we examine the mud recently thrown out from
a pond or canal in which there are shells. If the mud be argillaceous, it
acquires consistency on drying, and on breaking open a portion of it we find
that each shell has left impressions of its external form. If we then remove
the shell itself, we find within a solid nucleus of clay, having the form of the
interior of the shell. This form is often very different from that of the outer
shell. Thus a cast such as a, Fig. 51, commonly called a fossil screw, would
never be suspected by an inexperienced conchologist to be the internal
shape of the fossil univalve, b, Fig. 51. Nor should we have imagined at
first sight that the shell a and the cast b, Fig. 52, belong to one and the same
fossil. The reader will observe, in the last-mentioned figure (b, Fig. 52), that

an empty space shaded dark, which the shell itself once occupied, now
intervenes between the enveloping stone and the cast of the smooth interior
of the whorls. In such cases the shell has been dissolved and the component
particles removed by water percolating the rock. If the nucleus were taken
out, a hollow mould would remain, on which the external form of the shell
with its tubercles and striæ, as seen in a, Fig. 52, would be seen embossed.
Now if the space alluded to between the nucleus and the impression, instead
of being left empty, has been filled up with calcareous spar, flint, pyrites, or
other mineral, we then obtain from the mould an exact cast both of the
external and internal form of the original shell. In this manner silicified
casts of shells have been formed; and if the mud or sand of the nucleus
happen to be incoherent, or soluble in acid, we can then procure in flint an
empty shell, which in shape is the exact counterpart of the original. This
cast may be compared to a bronze statue, representing merely the
superficial form, and not the internal organisation; but there is another
description of petrifaction by no means uncommon, and of a much more
wonderful kind, which may be compared to certain anatomical models in
wax, where not only the outward forms and features, but the nerves, blood-
vessels, and other internal organs are also shown. Thus we find corals,
originally calcareous, in which not only the general shape, but also the
minute and complicated internal organisation is retained in flint.

Such a process of petrifaction is still more remarkably exhibited in fossil
wood, in which we often perceive not only the rings of annual growth, but
all the minute vessels and medullary rays. Many of the minute cells and
fibres of plants, and even those spiral vessels which in the living vegetable
can only be discovered by the microscope, are preserved. Among many
instances, I may mention a fossil tree, seventy-two feet in length, found at
Gosforth, near Newcastle, in sandstone strata associated with coal. By
cutting a transverse slice so thin as to transmit light, and magnifying it
about fifty-five times, the texture, as seen in Fig. 53, is exhibited. A texture
equally minute and complicated has been observed in the wood of large
trunks of fossil trees found in the Craigleith quarry near Edinburgh, where
the stone was not in the slightest degree siliceous, but consisted chiefly of
carbonate of lime, with oxide of iron, alumina, and carbon. The parallel
rows of vessels here seen are the rings of annual growth, but in one part
they are imperfectly preserved, the wood having probably decayed before
the mineralising matter had penetrated to that portion of the tree.
In attempting to explain the process of petrifaction in such cases, we may
first assume that strata are very generally permeated by water charged with
minute portions of calcareous, siliceous, and other earths in solution. In
what manner they become so impregnated will be afterwards considered. If
an organic substance is exposed in the open air to the action of the sun and
rain, it will in time putrefy, or be dissolved into its component elements,
consisting usually of oxygen, hydrogen, nitrogen, and carbon. These will
readily be absorbed by the atmosphere or be washed away by rain, so that
all vestiges of the dead animal or plant disappear. But if the same
substances be submerged in water, they decompose more gradually; and if
buried in earth, still more slowly; as in the familiar example of wooden
piles or other buried timber. Now, if as fast as each particle is set free by
putrefaction in a fluid or gaseous state, a particle equally minute of

carbonate of lime, flint, or other mineral, is at hand ready to be precipitated,
we may imagine this inorganic matter to take the place just before left
unoccupied by the organic molecule. In this manner a cast of the interior of
certain vessels may first be taken, and afterwards the more solid walls of
the same may decay and suffer a like transmutation. Yet when the whole is
lapidified, it may not form one homogeneous mass of stone or metal. Some
of the original ligneous, osseous, or other organic elements may remain
mingled in certain parts, or the lapidifying substance itself may be
differently coloured at different times, or so crystallised as to reflect light
differently, and thus the texture of the original body may be faithfully
exhibited.
The student may perhaps ask whether, on chemical principles, we have
any ground to expect that mineral matter will be thrown down precisely in
those spots where organic decomposition is in progress? The following
curious experiments may serve to illustrate this point: Professor Goppert of
Breslau, with a view of imitating the natural process of petrifaction, steeped
a variety of animal and vegetable substances in waters, some holding
siliceous, others calcareous, others metallic matter in solution. He found
that in the period of a few weeks, or sometimes even days, the organic
bodies thus immersed were mineralised to a certain extent. Thus, for
example, thin vertical slices of deal, taken from the Scotch fir (Pinus
sylvestris), were immersed in a moderately strong solution of sulphate of
iron. When they had been thoroughly soaked in the liquid for several days
they were dried and exposed to a red-heat until the vegetable matter was
burnt up and nothing remained but an oxide of iron, which was found to
have taken the form of the deal so exactly that casts even of the dotted
vessels peculiar to this family of plants were distinctly visible under the
microscope.
The late Dr. Turner observes, that when mineral matter is in a “nascent
state,” that is to say, just liberated from a previous state of chemical
combination, it is most ready to unite with other matter, and form a new
chemical compound. Probably the particles or atoms just set free are of
extreme minuteness, and therefore move more freely, and are more ready to
obey any impulse of chemical affinity. Whatever be the cause, it clearly
follows, as before stated, that where organic matter newly imbedded in
sediment is decomposing, there will chemical changes take place most
actively.

An analysis was lately made of the water which was flowing off from the
rich mud deposited by the Hooghly River in the Delta of the Ganges after
the annual inundation. This water was found to be highly charged with
carbonic acid holding lime in solution.[2] Now if newly-deposited mud is
thus proved to be permeated by mineral matter in a state of solution, it is
not difficult to perceive that decomposing organic bodies, naturally
imbedded in sediment, may as readily become petrified as the substances
artificially immersed by Professor Goppert in various fluid mixtures.
It is well known that the waters of all springs are more or less charged
with earthy, alkaline, or metallic ingredients derived from the rocks and
mineral veins through which they percolate. Silex is especially abundant in
hot springs, and carbonate of lime is almost always present in greater or less
quantity. The materials for the petrifaction of organic remains are, therefore,
usually at hand in a state of chemical solution wherever organic remains are
imbedded in new strata.
[1] Dr. MacCulloch, Syst. of Geol., vol. i, p. 123.

[2] Piddington, Asiat. Research., vol. xviii, p. 226.

CHAPTER V.
ELEVATION OF STRATA ABOVE THE SEA.—
HORIZONTAL AND INCLINED
STRATIFICATION.

Why the Position of Marine Strata, above the Level of the
Sea, should be referred to the rising up of the Land, not to
the going down of the Sea. — Strata of Deep-sea and
Shallow-water Origin alternate. — Also Marine and Fresh-
water Beds and old Land Surfaces. — Vertical, inclined, and
folded Strata. — Anticlinal and Synclinal Curves. —
Theories to explain Lateral Movements. — Creeps in Coal-
mines. — Dip and Strike. — Structure of the Jura. —
Various Forms of Outcrop. — Synclinal Strata forming
Ridges. — Connection of Fracture and Flexure of Rocks. —
Inverted Strata. — Faults described. — Superficial Signs of
the same obliterated by Denudation. — Great Faults the
Result of repeated Movements. — Arrangement and
Direction of parallel Folds of Strata. — Unconformability.
— Overlapping Strata.

Land has been raised, not the Sea lowered.—It has been already stated
that the aqueous rocks containing marine fossils extend over wide
continental tracts, and are seen in mountain chains rising to great heights
above the level of the sea (p. 29). Hence it follows, that what is now dry
land was once under water. But if we admit this conclusion, we must
imagine, either that there has been a general lowering of the waters of the
ocean, or that the solid rocks, once covered by water, have been raised up
bodily out of the sea, and have thus become dry land. The earlier geologists,

finding themselves reduced to this alternative, embraced the former
opinion, assuming that the ocean was originally universal, and had
gradually sunk down to its actual level, so that the present islands and
continents were left dry. It seemed to them far easier to conceive that the
water had gone down, than that solid land had risen upward into its present
position. It was, however, impossible to invent any satisfactory hypothesis
to explain the disappearance of so enormous a body of water throughout the
globe, it being necessary to infer that the ocean had once stood at whatever
height marine shells might be detected. It moreover appeared clear, as the
science of geology advanced, that certain spaces on the globe had been
alternately sea, then land, then estuary, then sea again, and, lastly, once
more habitable land, having remained in each of these states for
considerable periods. In order to account for such phenomena without
admitting any movement of the land itself, we are required to imagine
several retreats and returns of the ocean; and even then our theory applies
merely to cases where the marine strata composing the dry land are
horizontal, leaving unexplained those more common instances where strata
are inclined, curved, or placed on their edges, and evidently not in the
position in which they were first deposited.
Geologists, therefore, were at last compelled to have recourse to the
doctrine that the solid land has been repeatedly moved upward or
downward, so as permanently to change its position relatively to the sea.
There are several distinct grounds for preferring this conclusion. First, it
will account equally for the position of those elevated masses of marine
origin in which the stratification remains horizontal, and for those in which
the strata are disturbed, broken, inclined, or vertical. Secondly, it is
consistent with human experience that land should rise gradually in some
places and be depressed in others. Such changes have actually occurred in
our own days, and are now in progress, having been accompanied in some
cases by violent convulsions, while in others they have proceeded so
insensibly as to have been ascertainable only by the most careful scientific
observations, made at considerable intervals of time. On the other hand,
there is no evidence from human experience of a rising or lowering of the
sea’s level in any region, and the ocean cannot be raised or depressed in one
place without its level being changed all over the globe.
These preliminary remarks will prepare the reader to understand the great
theoretical interest attached to all facts connected with the position of strata,

whether horizontal or inclined, curved or vertical.
Now the first and most simple appearance is where strata of marine
origin occur above the level of the sea in horizontal position. Such are the
strata which we meet with in the south of Sicily, filled with shells for the
most part of the same species as those now living in the Mediterranean.
Some of these rocks rise to the height of more than 2000 feet above the sea.
Other mountain masses might be mentioned, composed of horizontal strata
of high antiquity, which contain fossil remains of animals wholly dissimilar
from any now known to exist. In the south of Sweden, for example, near
Lake Wener, the beds of some of the oldest fossiliferous deposits, called
Silurian and Cambrian by geologists, occur in as level a position as if they
had recently formed part of the delta of a great river, and been left dry on
the retiring of the annual floods. Aqueous rocks of equal antiquity extend
for hundreds of miles over the lake-district of North America, and exhibit in
like manner a stratification nearly undisturbed. The Table Mountain at the
Cape of Good Hope is another example of highly elevated yet perfectly
horizontal strata, no less than 3500 feet in thickness, and consisting of
sandstone of very ancient date.
Instead of imagining that such fossiliferous rocks were always at their
present level, and that the sea was once high enough to cover them, we
suppose them to have constituted the ancient bed of the ocean, and to have
been afterwards uplifted to their present height. This idea, however startling
it may at first appear, is quite in accordance, as before stated, with the
analogy of changes now going on in certain regions of the globe. Thus, in
parts of Sweden, and the shores and islands of the Gulf of Bothnia, proofs
have been obtained that the land is experiencing, and has experienced for
centuries, a slow upheaving movement.[1]
It appears from the observations of Mr. Darwin and others, that very
extensive regions of the continent of South America have been undergoing
slow and gradual upheaval, by which the level plains of Patagonia, covered
with recent marine shells, and the Pampas of Buenos Ayres, have been
raised above the level of the sea. On the other hand, the gradual sinking of
the west coast of Greenland, for the space of more than 600 miles from
north to south, during the last four centuries, has been established by the
observations of a Danish naturalist, Dr. Pingel. And while these proofs of
continental elevation and subsidence, by slow and insensible movements,

have been recently brought to light, the evidence has been daily
strengthened of continued changes of level effected by violent convulsions
in countries where earthquakes are frequent. There the rocks are rent from
time to time, and heaved up or thrown down several feet at once, and
disturbed in such a manner as to show how entirely the original position of
strata may be modified in the course of centuries.
Mr. Darwin has also inferred that, in those seas where circular coral
islands and barrier reefs abound, there is a slow and continued sinking of
the submarine mountains on which the masses of coral are based; while
there are other areas of the South Sea where the land is on the rise, and
where coral has been upheaved far above the sea-level.
Alternations of Marine and Fresh-water Strata.—It has been shown in
the third chapter that there is such a differencebetween land, fresh-water,
and marine fossils as to enable the geologist to determine whether particular
groups of strata were formed at the bottom of the ocean or in estuaries,
rivers, or lakes. If surprise was at first created by the discovery of marine
corals and shells at the height of several miles above the sea-level, the
imagination was afterwards not less startled by observing that in the
successive strata composing the earth’s crust, especially if their total
thickness amounted to thousands of feet, they comprised in some parts
formations of shallow-sea as well as of deep-sea origin; also beds of
brackish or even of purely fresh-water formation, as well as vegetable
matter or coal accumulated on ancient land. In these cases we as frequently
find fresh-water beds below a marine set or shallow-water under those of
deep-sea origin as the reverse. Thus, if we bore an artesian well below
London, we pass through a marine clay, and there reach, at the depth of
several hundred feet, a shallow-water and fluviatile sand, beneath which
comes the white chalk originally formed in a deep sea. Or if we bore
vertically through the chalk of the North Downs, we come, after traversing
marine chalky strata, upon a fresh-water formation many hundreds of feet
thick, called the Wealden, such as is seen in Kent and Surrey, which is
known in its turn to rest on purely marine beds. In like manner, in various
parts of Great Britain we sink vertical shafts through marine deposits of
great thickness, and come upon coal which was formed by the growth of
plants on an ancient land-surface sometimes hundreds of square miles in
extent.

Vertical, Inclined, and Curved Strata.—It has been stated that marine
strata of different ages are sometimes found at a considerable height above
the sea, yet retaining their original horizontality; but this state of things is
quite exceptional. As a general rule, strata are inclined or bent in such a
manner as to imply that their original position has been altered.

The most unequivocal evidence of such a change is afforded by their
standing up vertically, showing their edges, which is by no means a rare
phenomenon, especially in mountainous countries. Thus we find in
Scotland, on the southern skirts of the Grampians, beds of pudding-stone
alternating with thin layers of fine sand, all placed vertically to the horizon.
When Saussure first observed certain conglomerates in a similar position in
the Swiss Alps, he remarked that the pebbles, being for the most part of an
oval shape, had their longer axes parallel to the planes of stratification (see
Fig. 54 on preceding page). From this he inferred that such strata must, at
first, have been horizontal, each oval pebble having settled at the bottom of
the water, with its flatter side parallel to the horizon, for the same reason
that an egg will not stand on either end if unsupported. Some few, indeed,
of the rounded stones in a conglomerate occasionally afford an exception to
the above rule, for the same reason that in a river’s bed, or on a shingle
beach, some pebbles rest on their ends or edges; these having been shoved
against or between other stones by a wave or current, so as to assume this
position.
Anticlinal and Synclinal Curves.—Vertical strata, when they can be
traced continuously upward or downward for some depth, are almost
invariably seen to be parts of great curves, which may have a diameter of a
few yards, or of several miles. I shall first describe two curves of
considerable regularity, which occur in Forfarshire, extending over a
country twenty miles in breadth, from the foot of the Grampians to the sea
near Arbroath.

The mass of strata here shown may be 2000 feet in thickness, consisting
of red and white sandstone, and various coloured shales, the beds being
distinguishable into four principal groups, namely, No. 1, red marl or shale;
No. 2, red sandstone, used for building; No. 3, conglomerate; and No. 4,
grey paving-stone, and tile-stone, with green and reddish shale, containing
peculiar organic remains. A glance at the section will show that each of the
formations 2, 3, 4 are repeated thrice at the surface, twice with a southerly,
and once with a northerly inclination or dip, and the beds in No. 1, which
are nearly horizontal, are still brought up twice by a slight curvature to the
surface, once on each side of A. Beginning at the north-west extremity, the
tile-stones and conglomerates, No. 4 and No. 3, are vertical, and they
generally form a ridge parallel to the southern skirts of the Grampians. The
superior strata, Nos. 2 and 1, become less and less inclined on descending
to the valley of Strathmore, where the strata, having a concave bend, are
said by geologists to lie in a “trough” or“basin.” Through the centre of this
valley runs an imaginary line A, called technically a “synclinal line,” where
the beds, which are tilted in opposite directions, may be supposed to meet.
It is most important for the observer to mark such lines, for he will perceive
by the diagram that, in travelling from the north to the centre of the basin,
he is always passing from older to newer beds; whereas, after crossing the
line A, and pursuing his course in the same southerly direction, he is
continually leaving the newer, and advancing upon older strata. All the
deposits which he had before examined begin then to recur in reversed
order, until he arrives at the central axis of the Sidlaw hills, where the strata
are seen to form an arch, or saddle, having an anticlinal line, B, in the
centre. On passing this line, and continuing towards the S.E., the formations
4, 3, and 2, are again repeated, in the same relative order of superposition,
but with a southerly dip. At Whiteness (see Fig. 55) it will be seen that the

inclined strata are covered by a newer deposit, a, in horizontal beds. These
are composed of red conglomerate and sand, and are newer than any of the
groups, 1, 2, 3, 4, before described, and rest unconformably upon strata of
the sandstone group, No. 2.
An example of curved strata, in which the bends or convolutions of the
rock are sharper and far more numerous within an equal space, has been
well described by Sir James Hall.[2] It occurs near St. Abb’s Head, on the
east coast of Scotland, where the rocks consist principally of a bluish slate,
having frequently a ripple-marked surface. The undulations of the beds
reach from the top to the bottom of cliffs from 200 to 300 feet in height, and
there are sixteen distinct bendings in the course of about six miles, the
curvatures being alternately concave and convex upward.
Folding by Lateral Movement.—An experiment was made by Sir
James Hall, with a view of illustrating the manner in which such strata,
assuming them to have been originally horizontal, may have been forced
into their present position. A set of layers of clay were placed under a
weight, and their opposite ends pressed towards each other with such force
as to cause them to approach more nearly together. On the removal of the
weight, the layers of clay were found to be curved and folded, so as to bear
a miniature resemblance to the strata in the cliffs. We must, however, bear
in mind that in the natural section or sea-cliff we only see the foldings
imperfectly, one part being invisible beneath the sea, and the other, or upper
portion, being supposed to have been carried away by denudation, or that
action of water which will be explained in the next chapter. The dark lines
in the plan (Fig. 57) represent what is actually seen of the strata in the line
of cliff alluded to; the fainter lines, that portion which is concealed beneath
the sea-level, as also that which is supposed to have once existed above the
present surface.

We may still more easily illustrate the effects which a lateral thrust might
produce on flexible strata, by placing several pieces of differently coloured
cloths upon a table, and when they are spread out horizontally, cover them
with a book. Then apply other books to each end, and force them towards
each other. The folding of the cloths (see Fig. 58) will imitate those of the
bent strata; the incumbent book being slightly lifted up, and no longer
touching the two volumes on which it rested before, because it is supported
by the tops of the anticlinal ridges formed by the curved cloths. In like
manner there can be no doubt that the squeezed strata, although laterally
condensed and more closely packed, are yet elongated and made to rise
upward, in a direction perpendicular to the pressure.

Whether the analogous flexures in stratified rocks have really been due to
similar sideway movements is a question which we can not decide by
reference to our own observation. Our inability to explain the nature of the
process is, perhaps, not simply owing to the inaccessibility of the
subterranean regions where the mechanical force is exerted, but to the
extreme slowness of the movement. The changes may sometimes be due to
variation in the temperature of mountain masses of rock causing them,
while still solid, to expand or contract; or melting them, and then again
cooling them and allowing them to crystallise. If such be the case, we have
scarcely more reason to expect to witness the operation of the process
within the limited periods of our scientific observation than to see the
swelling of the roots of a tree, by which, in the course of years, a wall of
solid masonry may be lifted up, rent or thrown down. In both instances the
force may be irresistible, but though adequate, it need not be visible by us,
provided the time required for its development be very great. The lateral
pressure arising from the unequal expansion of rocks by heat may cause one
mass lying in the same horizontal plane gradually to occupy a larger space,
so as to press upon another rock, which, if flexible, may be squeezed into a
bent and folded form. It will also appear, when the volcanic and granitic
rocks are described, that some of them have, when melted in the interior of
the earth’s crust, been injected forcibly into fissures, and after the
solidification of such intruded matter, other sets of rents, crossing the first,
have been formed and in their turn filled by melted rock. Such repeated
injections imply a stretching, and often upheaval, of the whole mass.
We also know, especially by the study of regions liable to earthquakes,
that there are causes at work in the interior of the earth capable of
producing a sinking in of the ground, sometimes very local, but often
extending over a wide area. The continuance of such a downward

movement, especially if partial and confined to linear areas, may produce
regular folds in the strata.
Creeps in Coal-mines.—The “creeps,” as they are called in coal-mines,
afford an excellent illustration of this fact.—First, it may be stated
generally, that the excavation of coal at a considerable depth causes the
mass of overlying strata to sink down bodily, even when props are left to
support the roof of the mine. “In Yorkshire,” says Mr. Buddle, “three
distinct subsidences were perceptible at the surface, after the clearing out of
three seams of coal below, and innumerable vertical cracks were caused in
the incumbent mass of sandstone and shale which thus settled down.”[3] The
exact amount of depression in these cases can only be accurately measured
where water accumulates on the surface, or a railway traverses a coal-field.
When a bed of coal is worked out, pillars or rectangular masses of coal
are left at intervals as props to support the roof, and protect the colliers.
Thus in Fig. 59, representing a section at Wallsend, Newcastle, the galleries
which have been excavated are represented by the white spaces a, b, while
the adjoining dark portions are parts of the original coal seam left as props,
beds of sandy clay or shale constituting the floor of the mine. When the
props have been reduced in size, they are pressed down by the weight of
overlying rocks (no less than 630 feet thick) upon the shale below, which is
thereby squeezed and forced up into the open spaces.
Now it might have been expected that, instead of the floor rising up, the
ceiling would sink down, and this effect, called a “thrust,” does, in fact, take
place where the pavement is more solid than the roof. But it usually
happens, in coal-mines, that the roof is composed of hard shale, or
occasionally of sandstone, more unyielding than the foundation, which
often consists of clay. Even where the argillaceous substrata are hard at
first, they soon become softened and reduced to a plastic state when
exposed to the contact of air and water in the floor of a mine.

The first symptom of a “creep,” says Mr. Buddle, is a slight curvature at
the bottom of each gallery, as at a, Fig. 59: then the pavement, continuing to
rise, begins to open with a longitudinal crack, as at b; then the points of the
fractured ridge reach the roof, as at c; and, lastly, the upraised beds close up
the whole gallery, and the broken portions of the ridge are reunited and
flattened at the top, exhibiting the flexure seen at d. Meanwhile the coal in
the props has become crushed and cracked by pressure. It is also found that
below the creeps a, b, c, d, an inferior stratum, called the “metal coal,”
which is 3 feet thick, has been fractured at the points e, f, g, h, and has risen,
so as to prove that the upward movement, caused by the working out of the
“main coal,” has been propagated through a thickness of 54 feet of
argillaceous beds, which intervene between the two coal-seams. This same
displacement has also been traced downward more than 150 feet below the
metal coal, but it grows continually less and less until it becomes
imperceptible.
No part of the process above described is more deserving of our notice
than the slowness with which the change in the arrangement of the beds is
brought about. Days, months, or even years, will sometimes elapse between
the first bending of the pavement and the time of its reaching the roof.
Where the movement has been most rapid, the curvature of the beds is most
regular, and the reunion of the fractured ends most complete; whereas the
signs of displacement or violence are greatest in those creeps which have
required months or years for their entire accomplishment. Hence we may
conclude that similar changes may have been wrought on a larger scale in
the earth’s crust by partial and gradual subsidences, especially where the

ground has been undermined throughout long periods of time; and we must
be on our guard against inferring sudden violence, simply because the
distortion of the beds is excessive.
Engineers are familiar with the fact that when they raise the level of a
railway by heaping stone or gravel on a foundation of marsh, quicksand, or
other yielding formation, the new mound often sinks for a time as fast as
they attempt to elevate it; when they have persevered so as to overcome this
difficulty, they frequently find that some of the adjoining flexible ground
has risen up in one or more parallel arches or folds, showing that the
vertical pressure of the sinking materials has given rise to a lateral folding
movement.
In like manner, in the interior of the earth, the solid parts of the earth’s
crust may sometimes, as before mentioned, be made to expand by heat, or
may be pressed by the force of steam against flexible strata loaded with a
great weight of incumbent rocks. In this case the yielding mass, squeezed,
but unable to overcome the resistance which it meets with in a vertical
direction, may be gradually relieved by lateral folding.

Dip and Strike.—In describing the manner in which strata depart from
their original horizontality, some technical terms, such as “dip” and
“strike,” “anticlinal” and “synclinal” line or axis, are used by geologists. I
shall now proceed to explain some of these to the student. If a stratum or
bed of rock, instead of being quite level, be inclined to one side, it is said to
dip; the point of the compass to which it is inclined is called the point of
dip, and the degree of deviation from a level or horizontal line is called the
amount of dip, or the angle of dip. Thus, in the annexed diagram (Fig. 60), a
series of strata are inclined, and they dip to the north at an angle of forty-
five degrees. The strike, or line of bearing, is the prolongation or extension
of the strata in a direction at right angles to the dip; and hence it is
sometimes called the direction of the strata. Thus, in the above instance of
strata dipping to the north, their strike must necessarily be east and west.
We have borrowed the word from the German geologists, streichen
signifying to extend, to have a certain direction. Dip and strike may be aptly

illustrated by a row of houses running east and west, the long ridge of the
roof representing the strike of the stratum of slates, which dip on one side to
the north, and on the other to the south.
A stratum which is horizontal, or quite level in all directions, has neither
dip nor strike.
It is always important for the geologist, who is endeavouring to
comprehend the structure of a country, to learn how the beds dip in every
part of the district; but it requires some practice to avoid being occasionally
deceived, both as to the point of dip and the amount of it.

If the upper surface of a hard stony stratum be uncovered, whether
artificially in a quarry, or by waves at the foot of a cliff, it is easy to
determine towards what point of the compass the slope is steepest, or in
what direction water would flow if poured upon it. This is the true dip. But
the edges of highly inclined strata may give rise to perfectly horizontal lines
in the face of a vertical cliff, if the observer see the strata in the line of the
strike, the dip being inward from the face of the cliff. If, however, we come
to a break in the cliff, which exhibits a section exactly at right angles to the
line of the strike, we are then able to ascertain the true dip. In the drawing
(Fig. 61), we may suppose a headland, one side of which faces to the north,
where the beds would appear perfectly horizontal to a person in the boat;
while in the other side facing the west, the true dip would be seen by the
person on shore to be at an angle of 40°. If, therefore, our observations are
confined to a vertical precipice facing in one direction, we must endeavour
to find a ledge or portion of the plane of one of the beds projecting beyond
the others, in order to ascertain the true dip.

If not provided with a clinometer, a most useful instrument, when it is of
consequence to determine with precision the inclination of the strata, the
observer may measure the angle within a few degrees by standing exactly
opposite to a cliff where the true dip is exhibited, holding the hands
immediately before the eyes, and placing the fingers of one in a
perpendicular, and of the other in a horizontal position, as in Fig. 62. It is
thus easy to discover whether the lines of the inclined beds bisect the angle
of 90°, formed by the meeting of the hands, so as to give an angle of 45°, or
whether it would divide the space into two equal or unequal portions. You
have only to change hands to get the line of dip on the upper side of the
horizontal hand.

It has been already seen, in describing the curved strata on the east coast
of Scotland, in Forfarshire and Berwickshire, that a series of concave and
convex bendings are occasionally repeated several times. These usually
form part of a series of parallel waves of strata, which are prolonged in the
same direction, throughout a considerable extent of country. Thus, for
example, in the Swiss Jura, that lofty chain of mountains has been proved to
consist of many parallel ridges, with intervening longitudinal valleys, as in
Fig. 63, the ridges being formed by curved fossiliferous strata, of which the
nature and dip are occasionally displayed in deep transverse gorges, called

“cluses,” caused by fractures at right angles to the direction of the chain.[4]
Now let us suppose these ridges and parallel valleys to run north and south,
we should then say that the strike of the beds is north and south, and the dip
east and west. Lines drawn along the summits of the ridges, A, B, would be
anticlinal lines, and one following the bottom of the adjoining valleys a
synclinal line.

Outcrop of Strata.—It will be observed that some of these ridges, A, B,
are unbroken on the summit, whereas one of them, C, has been fractured
along the line of strike, and a portion of it carried away by denudation, so
that the ridges of the beds in the formations a, b, c come out to the day, or,
as the miners say, crop out, on the sides of a valley. The ground-plan of
such a denuded ridge as C, as given in a geological map, may be expressed
by the diagram, Fig. 64, and the cross-section of the same by Fig. 65. The
line D E, Fig. 64, is the anticlinal line, on each side of which the dip is in
opposite directions, as expressed by the arrows. The emergence of strata at
the surface is called by miners their outcrop, or basset.
If, instead of being folded into parallel ridges, the beds form a boss or
dome-shaped protuberance, and if we suppose the summit of the dome
carried off, the ground-plan would exhibit the edges of the strata forming a
succession of circles, or ellipses, round a common centre. These circles are
the lines of strike, and the dip being always at right angles is inclined in the
course of the circuit to every point of the compass, constituting what is
termed a quâ-quâversal dip—that is, turning every way.
There are endless variations in the figures described by the basset-edges
of the strata, according to the different inclination of the beds, and the mode
in which they happen to have been denuded. One of the simplest rules, with
which every geologist should be acquainted, relates to the V-like form of
the beds as they crop out in an ordinary valley. First, if the strata be
horizontal, the V-like form will be also on a level, and the newest strata will
appear at the greatest heights.

Secondly, if the beds be inclined and intersected by a valley sloping in
the same direction, and the dip of the beds be less steep than the slope of the
valley, then the V’s, as they are often termed by miners, will point upward
(see Fig. 66), those formed by the newer beds appearing in a superior
position, and extending highest up the valley, as A is seen above B.
Thirdly, if the dip of the beds be steeper than the slope of the valley, then
the V’s will point downward (see Fig. 67), and those formed of the older
beds will now appear uppermost, as B appears above A.
Fourthly, in every case where the strata dip in a contrary direction to the
slope of the valley, whatever be the angle of inclination, the newer beds will

appear the highest, as in the first and second cases. This is shown by the
drawing (Fig. 68), which exhibits strata rising at an angle of 20°, and
crossed by a valley, which declines in an opposite direction at 20°.
These rules may often be of great practical utility; for the different
degrees of dip occurring in the two cases represented in Figs. 66 and 67
may occasionally be encountered in following the same line of flexure at
points a few miles distant from each other. A miner unacquainted with the
rule, who had first explored the valley Fig. 66, may have sunk a vertical
shaft below the coal-seam A, until he reached the inferior bed, B. He might
then pass to the valley, Fig. 67, and discovering there also the outcrop of
two coal-seams, might begin his workings in the uppermost in the
expectation of coming down to the other bed A, which would be observed
cropping out lower down the valley. But a glance at the section will
demonstrate the futility of such hopes.[5]

Section of carboniferous rocks of Lancashire. (E. Hull.[6])

Synclinal Strata forming Ridges.—Although in many cases an
anticlinal axis forms a ridge, and a synclinal axis a valley, as in A B, Fig.
63, yet this can by no means be laid down as a general rule, as the beds very
often slope inward from either side of a mountain, as at a, b, Fig. 69, while
in the intervening valley, c, they slope upward, forming an arch.
It would be natural to expect the fracture of solid rocks to take place
chiefly where the bending of the strata has been sharpest, and such rending
may produce ravines giving access to running water and exposing the
surface to atmospheric waste. The entire absence, however, of such cracks
at points where the strain must have been greatest, as at a, Fig. 63, is often
very remarkable, and not always easy of explanation. We must imagine that
many strata of limestone, chert, and other rocks which are now brittle, were
pliant when bent into their present position. They may have owed their
flexibility in part to the fluid matter which they contained in their minute

pores, as before described p. 62 and in part to the permeation of sea-water
while they were yet submerged.

At the western extremity of the Pyrenees, great curvatures of the strata
are seen in the sea-cliffs, where the rocks consist of marl, grit, and chert. At
certain points, as at a, Fig. 70, some of the bendings of the flinty chert are
so sharp that specimens might be broken off well fitted to serve as ridge-
tiles on the roof of a house. Although this chert could not have been brittle
as now, when first folded into this shape, it presents, nevertheless, here and
there, at the points of greatest flexure, small cracks, which show that it was
solid, and not wholly incapable of breaking at the period of its
displacement. The numerous rents alluded to are not empty, but filled with
chalcedony and quartz.

Between San Caterina and Castrogiovanni, in Sicily, bent and undulating
gypseous marls occur, with here and there thin beds of solid gypsum
interstratified. Sometimes these solid layers have been broken into detached
fragments, still preserving their sharp edges (g, g, Fig. 71), while the
continuity of the more pliable and ductile marls, m, m, has not been
interrupted.

We have already explained, Fig. 69, that stratified rocks have usually
their strata bent into parallel folds forming anticlinal and synclinal axes, a
group of several of these folds having often been subjected to a common
movement, and having acquired a uniform strike or direction. In some

disturbed regions these folds have been doubled back upon themselves in
such a manner that it is often difficult for an experienced geologist to
determine correctly the relative age of the beds by superposition. Thus, if
we meet with the strata seen in the section, Fig. 72, we should naturally
suppose that there were twelve distinct beds, or sets of beds, No. 1 being the
newest, and No. 12 the oldest of the series. But this section may perhaps
exhibit merely six beds, which have been folded in the manner seen in Fig.
73, so that each of them is twice repeated, the position of one half being
reversed, and part of No. 1, originally the uppermost, having now become
the lowest of the series.

These phenomena are observable on a magnificent scale in certain
regions in Switzerland, in precipices often more than 2000 feet in
perpendicular height, and there are flexures not inferior in dimensions in the
Pyrenees. The upper part of the curves seen in this diagram, Fig. 73, and
expressed in fainter lines, has been removed by what is called denudation,
to be afterwards explained.
Fractures of the Strata and Faults.—Numerous rents may often be
seen in rocks which appear to have been simply broken, the fractured parts
still remaining in contact; but we often find a fissure, several inches or
yards wide, intervening between the disunited portions. These fissures are
usually filled with fine earth and sand, or with angular fragments of stone,
evidently derived from the fracture of the contiguous rocks.
The face of each wall of the fissure is often beautifully polished, as if
glazed, striated, or scored with parallel furrows and ridges, such as would
be produced by the continued rubbing together of surfaces of unequal
hardness. These polished surfaces are called by miners “slickensides.” It is
supposed that the lines of the striæ indicate the direction in which the rocks
were moved. During one of the minor earthquakes in Chili, in 1840, the
brick walls of a building were rent vertically in several places, and made to

vibrate for several minutes during each shock, after which they remained
uninjured, and without any opening, although the line of each crack was
still visible. When all movement had ceased, there were seen on the floor of
the house, at the bottom of each rent, small heaps of fine brick-dust,
evidently produced by trituration.
It is not uncommon to find the mass of rock on one side of a fissure
thrown up above or down below the mass with which it was once in contact
on the other side. “This mode of displacement is called a fault, shift, slip, or
throw.” “The miner,” says Playfair, describing a fault, “is often perplexed,
in his subterranean journey, by a derangement in the strata, which changes
at once all those lines and bearings which had hitherto directed his course.
When his mine reaches a certain plane, which is sometimes perpendicular,
as in A B, Fig. 74, sometimes oblique to the horizon (as in C D, ibid.), he
finds the beds of rock broken asunder, those on the one side of the plane
having changed their place, by sliding in a particular direction along the
face of the others. In this motion they have sometimes preserved their
parallelism, as in Fig. 74, so that the strata on each side of faults A B, C D,
continue parallel to one another; in other cases, the strata on each side are
inclined, as in a, b, c, d (Fig. 75), though their identity is still to be
recognised by their possessing the same thickness and the same internal
characters.”[7]

In Coalbrook Dale, says Mr. Prestwich[8], deposits of sandstone, shale,
and coal, several thousand feet thick, and occupying an area of many miles,

have been shivered into fragments, and the broken remnants have been
placed in very discordant positions, often at levels differing several hundred
feet from each other. The sides of the faults, when perpendicular, are
commonly several yards apart, and are sometimes as much as 50 yards
asunder, the interval being filled with broken débris of the strata. In
following the course of the same fault it is sometimes found to produce in
different places very unequal changes of level, the amount of shift being in
one place 300, and in another 700 feet, which arises from the union of two
or more faults. In other words, the disjointed strata have in certain districts
been subjected to renewed movements, which they have not suffered
elsewhere.
We may occasionally see exact counterparts of these slips, on a small
scale, in pits of loose sand and gravel, many of which have doubtless been
caused by the drying and shrinking of argillaceous and other beds, slight
subsidences having taken place from failure of support. Sometimes,
however, even these small slips may have been produced during
earthquakes; for land has been moved, and its level, relatively to the sea,
considerably altered, within the period when much of the alluvial sand and
gravel now covering the surface of continents was deposited.
I have already stated that a geologist must be on his guard, in a region of
disturbed strata, against inferring repeated alternations of rocks, when, in
fact, the same strata, once continuous, have been bent round so as to recur
in the same section, and with the same dip. A similar mistake has often been
occasioned by a series of faults.

If, for example, the dark line A H (Fig. 76) represent the surface of a
country on which the strata a, b, c frequently crop out, an observer who is
proceeding from H to A might at first imagine that at every step he was

approaching new strata, whereas the repetition of the same beds has been
caused by vertical faults, or downthrows. Thus, suppose the original mass,
A, B, C, D, to have been a set of uniformly inclined strata, and that the
different masses under E F, F G, and G D sank down successively, so as to
leave vacant the spaces marked in the diagram by dotted lines, and to
occupy those marked by the continuous lines, then let denudation take place
along the line A H, so that the protruding masses indicated by the fainter
lines are swept away—a miner, who has not discovered the faults, finding
the mass a, which we will suppose to be a bed of coal four times repeated,
might hope to find four beds, workable to an indefinite depth, but first, on
arriving at the fault G, he is stopped suddenly in his workings, for he comes
partly upon the shale b, and partly on the sandstone c; the same result
awaits him at the fault F, and on reaching E he is again stopped by a wall
composed of the rock d.
The very different levels at which the separated parts of the same strata
are found on the different sides of the fissure, in some faults, is truly
astonishing. One of the most celebrated in England is that called the
“ninety-fathom dike,” in the coal-field of Newcastle. This name has been
given to it, because the same beds are ninety fathoms (540 feet) lower on
the northern than they are on the southern side. The fissure has been filled
by a body of sand, which is now in the state of sandstone, and is called the
dike, which is sometimes very narrow, but in other places more than twenty
yards wide.[9] The walls of the fissure are scored by grooves, such as would
have been produced if the broken ends of the rock had been rubbed along
the plane of the fault.[10] In the Tynedale and Craven faults, in the north of
England, the vertical displacement is still greater, and the fracture has
extended in a horizontal direction for a distance of thirty miles or more.
Great Faults the Result of Repeated Movements.—It must not,
however, be supposed that faults generally consist of single linear rents;
there are usually a number of faults springing off from the main one, and
sometimes a long strip of country seems broken up into fragments by sets of
parallel and connecting transverse faults. Oftentimes a great line of fault has
been repeated, or the movements have been continued through successive
periods, so that, newer deposits having covered the old line of
displacement, the strata both newer and older have given way along the old
line of fracture. Some geologists have considered it necessary to imagine
that the upward or downward movement in these cases was accomplished at

a single stroke, and not by a series of sudden but interrupted movements.
They appear to have derived this idea from a notion that the grooved walls
have merely been rubbed in one direction, which is far from being a
constant phenomenon. Not only are some sets of striæ not parallel to others,
but the clay and rubbish between the walls, when squeezed or rubbed, have
been streaked in different directions, the grooves which the harder minerals
have impressed on the softer being frequently curved and irregular.

The usual absence of protruding masses of rock forming precipices or
ridges along the lines of great faults has already been alluded to in
explaining Fig. 76, p. 89, and the same remarkable fact is well exemplified
in every coal-field which has been extensively worked. It is in such districts
that the former relation of the beds which have been shifted is determinable
with great accuracy. Thus in the coal-field of Ashby de la Zouch, in
Leicestershire (see Fig. 77), a fault occurs, on one side of which the coal-
beds a, b, c, d must once have risen to the height of 500 feet above the
corresponding beds on the other side. But the uplifted strata do not stand up
500 feet above the general surface; on the contrary, the outline of the
country, as expressed by the line z z, is uniformly undulating, without any
break, and the mass indicated by the dotted outline must have been washed
away.[11]
The student may refer to Mr. Hull’s measurement of faults, observed in
the Lancashire coal-field, where the vertical displacement has amounted to
thousands of feet, and yet where all the superficial inequalities which must
have resulted from such movements have been obliterated by subsequent
denudation. In the same memoir proofs are afforded of there having been
two periods of vertical movement in the same fault—one, for example,
before, and another after, the Triassic epoch.[12]
The shifting of the beds by faults is often intimately connected with those
same foldings which constitute the anticlinal and synclinal axes before

alluded to, and there is no doubt that the subterranean causes of both forms
of disturbance are to a great extent the same. A fault in Virginia, believed to
imply a displacement of several thousand feet, has been traced for more
than eighty miles in the same direction as the foldings of the Appalachian
chain.[13] An hypothesis which attributes such a change of position to a
succession of movements, is far preferable to any theory which assumes
each fault to have been accomplished by a single upcast or downthrow of
several thousand feet. For we know that there are operations now in
progress, at great depths in the interior of the earth, by which both large and
small tracts of ground are made to rise above and sink below their former
level, some slowly and insensibly, others suddenly and by starts, a few feet
or yards at a time; whereas there are no grounds for believing that, during
the last 3000 years at least, any regions have been either upheaved or
depressed, at a single stroke, to the amount of several hundred, much less
several thousand feet.
It is certainly not easy to understand how in the subterranean regions one
mass of solid rock should have been folded up by a continued series of
movements, while another mass in contact, or only separated by a line of
fissure, has remained stationary or has perhaps subsided. But every volcano,
by the intermittent action of the steam, gases, and lava evolved during an
eruption, helps us to form some idea of the manner in which such
operations take place. For eruptions are repeated at uncertain intervals
throughout the whole or a large part of a geological period, some of the
surrounding and contiguous districts remaining quite undisturbed. And in
most of the instances with which we are best acquainted the emission of
lava, scoria, and steam is accompanied by the uplifting of the solid crust.
Thus in Vesuvius, Etna, the Madeiras, the Canary Islands, and the Azores
there is evidence of marine deposits of recent and tertiary date having been
elevated to the height of a thousand feet, and sometimes more, since the
commencement of the volcanic explosions. There is, moreover, a general
tendency in contemporaneous volcanic vents to affect a linear arrangement,
extending in some instances, as in the Andes or the Indian Archipelago, to
distances equalling half the circumference of the globe. Where volcanic
heat, therefore, operates at such a depth as not to obtain vent at the surface,
in the form of an eruption, it may nevertheless be conceived to give rise to
upheavals, foldings, and faults in certain linear tracts. And marine
denudation, to be treated of in the next chapter, will help us to understand

why that which should be the protruding portion of the faulted rocks is
missing at the surface.
Arrangement and Direction of Parallel Folds of Strata.—The possible
causes of the folding of strata by lateral movements have been considered
in a former part of this chapter. No European chain of mountains affords so
remarkable an illustration of the persistency of such flexures for a great
distance as the Appalachians before alluded to, and none has been studied
and described by many good observers with more accuracy. The chain
extends from north to south, or rather N.N.E. to S.S.W., for nearly 1500
miles, with a breadth of 50 miles, throughout which the Palæozoic strata
have been so bent as to form a series of parallel anticlinal and synclinal
ridges and troughs, comprising usually three or four principal and many
smaller plications, some of them forming broad and gentle arches, others
narrower and steeper ones, while some, where the bending has been
greatest, have the position of their beds inverted, as before shown in Fig.
73, p. 87.
The strike of the parallel ridges, after continuing in a straight line for
many hundred miles, is then found to vary for a more limited distance as
much as 30°, the folds wheeling round together in the new direction and
continuing to be parallel, as if they had all obeyed the same movement. The
date of the movements by which the great flexures were brought about
must, of course, be subsequent to the formation of the uppermost part of the
coal or the newest of the bent rocks, but the disturbance must have ceased
before the Triassic strata were deposited on the denuded edges of the folded
beds.
The manner in which the numerous parallel folds, all simultaneously
formed, assume a new direction common to the whole of them, and
sometimes varying at an angle of 30° from the normal strike of the chain,
shows what deviation from an otherwise uniform strike of the beds may be
experienced when the geographical area through which they are traced is on
so vast a scale.
The disturbances in the case here adverted to occurred between the
Carboniferous period and that of the Trias, and this interval is so vast that
they may have occupied a great lapse of time, during which their
parallelism was always preserved. But, as a rule, wherever after a long
geological interval the recurrence of lateral movements gives rise to a new

set of folds, the strike of these last is different. Thus, for example, Mr. Hull
has pointed out that three principal lines of disturbance, all later than the
Carboniferous period, have affected the stratified rocks of Lancashire. The
first of these, having an E.N.E. direction, took place at the close of the
Carboniferous period. The next, running north and south, at the close of the
Permian, and the third, having a N.N.W. direction, at the close of the
Jurassic period.[14]

Unconformability of Strata.— Strata are said to be unconformable
when one series is so placed over another that the planes of the superior
repose on the edges of the inferior (see Fig. 78). In this case it is evident
that a period had elapsed between the production of the two sets of strata,
and that, during this interval, the older series had been tilted and disturbed.
Afterwards the upper series was thrown down in horizontal strata upon it. If
these superior beds, d, d, Fig. 78, are also inclined, it is plain that the lower
strata a, a, have been twice displaced; first, before the deposition of the
newer beds, d, d, and a second time when these same strata were upraised
out of the sea, and thrown slightly out of the horizontal position.

It often happens that in the interval between the deposition of two sets of
unconformable strata, the inferior rock has not only been denuded, but
drilled by perforating shells. Thus, for example, at Autreppe and Gusigny,
near Mons, beds of an ancient (primary or palæozoic) limestone, highly
inclined, and often bent, are covered with horizontal strata of greenish and
whitish marls of the Cretaceous formation. The lowest, and therefore the
oldest, bed of the horizontal series is usually the sand and conglomerate, a,

in which are rounded fragments of stone, from an inch to two feet in
diameter. These fragments have often adhering shells attached to them, and
have been bored by perforating mollusca. The solid surface of the inferior
limestone has also been bored, so as to exhibit cylindrical and pear-shaped
cavities, as at c, the work of saxicavous mollusca; and many rents, as at b,
which descend several feet or yards into the limestone, have been filled
with sand and shells, similar to those in the stratum a.
Overlapping Strata.—Strata are said to overlap when an upper bed
extends beyond the limits of a lower one. This may be produced in various
ways; as, for example, when alterations of physical geography cause the
arms of a river or channels of discharge to vary, so that sediment brought
down is deposited over a wider area than before, or when the sea-bottom
has been raised up and again depressed without disturbing the horizontal
position of the strata. In this case the newer strata may rest for the most part
conformably on the older, but, extending farther, pass over their edges.
Every intermediate state between unconformable and over-lapping beds
may occur, because there may be every gradation between a slight
derangement of position, and a considerable disturbance and denudation of
the older formation before the newer beds come on.
[1] See “Principles of Geology,” 1867, p. 314.

[2] Edin. Trans., vol. vii, pl. 3.

[3] Proceedings of Geol. Soc., vol. iii, p. 148.

[4] Thurmann, “Essai sur les Soulèvemens Jurassiques de Porrentruy,” Paris,
1832.

[5] I am indebted to the kindness of T. Sopwith, Esq., for three models which I
have copied in the above diagrams; but the beginner may find it by no means
easy to understand such copies, although, if he were to examine and handle the
originals, turning them about in different ways, he would at once comprehend
their meaning, as well as the import of others far more complicated, which the
same engineer has constructed to illustrate faults.

[6] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 324, 1868.

[7] Playfair, Illust. of Hutt. Theory, § 42.

[8] Geol. Trans., second series. vol. v, p. 452.

[9] Conybeare and Phillips Outlines, etc., p. 376.

[10] Phillips, Geology, Lardner’s Cyclop., p. 41.

[11] See Mammatt’s Geological Facts, etc., p. 90 and plate.

[12] Hull, Quart. Geol. Journ., vol. xxiv, p. 318, 1868.

[13] H. D. Rogers, Geol. of Pennsylvania, p. 897.

[14] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 323.

CHAPTER VI.
DENUDATION

Denudation defined. — Its Amount more than equal to the
entire Mass of Stratified Deposits in the Earth’s Crust. —
Subaërial Denudation. — Action of the Wind. — Action of
Running Water. — Alluvium defined. — Different Ages of
Alluvium. — Denuding Power of Rivers affected by Rise or
Fall of Land. — Littoral Denudation. — Inland Sea-Cliffs.
— Escarpments. — Submarine Denudation. — Dogger-
bank. — Newfoundland Bank. — Denuding Power of the
Ocean during Emergence of Land.

Denudation, which has been occasionally spoken of in the preceding
chapters, is the removal of solid matter by water in motion, whether of
rivers or of the waves and currents of the sea, and the consequent laying
bare of some inferior rock. This operation has exerted an influence on the
structure of the earth’s crust as universal and important as sedimentary
deposition itself; for denudation is the necessary antecedent of the
production of all new strata of mechanical origin. The formation of every
new deposit by the transport of sediment and pebbles necessarily implies
that there has been, somewhere else, a grinding down of rock into rounded
fragments, sand, or mud, equal in quantity to the new strata. All deposition,
therefore, except in the case of a shower of volcanic ashes, and the outflow
of lava, and the growth of certain organic formations, is the sign of
superficial waste going on contemporaneously, and to an equal amount,
elsewhere. The gain at one point is no more than sufficient to balance the
loss at some other. Here a lake has grown shallower, there a ravine has been
deepened. Here the depth of the sea has been augmented by the removal of
a sandbank during a storm, there its bottom has been raised and shallowed
by the accumulation in its bed of the same sand transported from the bank.

When we see a stone building, we know that somewhere, far or near, a
quarry has been opened. The courses of stone in the building may be
compared to successive strata, the quarry to a ravine or valley which has
suffered denudation. As the strata, like the courses of hewn stone, have been
laid one upon another gradually, so the excavation both of the valley and
quarry have been gradual. To pursue the comparison still farther, the
superficial heaps of mud, sand, and gravel, usually called alluvium, may be
likened to the rubbish of a quarry which has been rejected as useless by the
workmen, or has fallen upon the road between the quarry and the building,
so as to lie scattered at random over the ground.
But we occasionally find in a conglomerate large rounded pebbles of an
older conglomerate, which had previously been derived from a variety of
different rocks. In such cases we are reminded that, the same materials
having been used over and over again, it is not enough to affirm that the
entire mass of stratified deposits in the earth’s crust affords a monument and
measure of the denudation which has taken place, for in truth the quantity
of matter now extant in the form of stratified rock represents but a fraction
of the material removed by water and redeposited in past ages.
Subaërial Denudation.—Denudation may be divided into subaërial, or
the action of wind, rain, and rivers; and submarine, or that effected by the
waves of the sea, and its tides and currents. With the operation of the first of
these we are best acquainted, and it may be well to give it our first attention.
Action of the Wind.—In desert regions where no rain falls, or where, as in
parts of the Sahara, the soil is so salt as to be without any covering of
vegetation, clouds of dust and sand attest the power of the wind to cause the
shifting of the unconsolidated or disintegrated rock.
In examining volcanic countries I have been much struck with the great
superficial changes brought about by this power in the course of centuries.
The highest peak of Madeira is about 6050 feet above the sea, and consists
of the skeleton of a volcanic cone now 250 feet high, the beds of which
once dipped from a centre in all directions at an angle of more than 30°.
The summit is formed of a dike of basalt with much olivine, fifteen feet
wide, apparently the remains of a column of lava which once rose to the
crater. Nearly all the scoriæ of the upper part of the cone have been swept
away, those portions only remaining which were hardened by the contact or
proximity of the dike. While I was myself on this peak on January 25, 1854,

I saw the wind, though it was not stormy weather, removing sand and dust
derived from the decomposing scoriæ. There had been frost in the night,
and some ice was still seen in the crevices of the rock.
On the highest platform of the Grand Canary, at an elevation of 6000
feet, there is a cylindrical column of hard lava, from which the softer matter
has been carried away; and other similar remnants of the dikes of cones of
eruption attest the denuding power of the wind at points where running
water could never have exerted any influence. The waste effected by wind
aided by frost and snow, may not be trifling, even in a single winter, and
when multiplied by centuries may become indefinitely great.

Action of Running Water.—There are different classes of phenomena
which attest in a most striking manner the vast spaces left vacant by the
erosive power of water. I may allude, first, to those valleys on both sides of
which the same strata are seen following each other in the same order, and
having the same mineral composition and fossil contents. We may observe,
for example, several formations, as Nos. 1, 2, 3, 4, in the diagram (Fig. 80):
No. 1, conglomerate, No. 2, clay, No. 3, grit, and No. 4, limestone, each
repeated in a series of hills separated by valleys varying in depth. When we
examine the subordinate parts of these four formations, we find, in like
manner, distinct beds in each, corresponding, on the opposite sides of the
valleys, both in composition and order of position. No one can doubt that
the strata were originally continuous, and that some cause has swept away
the portions which once connected the whole series. A torrent on the side of
a mountain produces similar interruptions; and when we make artificial cuts
in lowering roads, we expose, in like manner, corresponding beds on either
side. But in nature, these appearances occur in mountains several thousand
feet high, and separated by intervals of many miles or leagues in extent.
In the “Memoirs of the Geological Survey of Great Britain” (vol. i),
Professor Ramsay has shown that the missing beds, removed from the
summit of the Mendips, must have been nearly a mile in thickness; and he
has pointed out considerable areas in South Wales and some of the adjacent

counties of England, where a series of primary (or palæozoic) strata, no less
than 11,000 feet in thickness, have been stripped off. All these materials
have of course been transported to new regions, and have entered into the
composition of more modern formations. On the other hand, it is shown by
observations in the same “Survey,” that the Palæozoic strata are from
20,000 to 30,000 feet thick. It is clear that such rocks, formed of mud and
sand, now for the most part consolidated, are the monuments of denuding
operations, which took place on a grand scale at a very remote period in the
earth’s history. For, whatever has been given to one area must always have
been borrowed from another; a truth which, obvious as it may seem when
thus stated, must be repeatedly impressed on the student’s mind, because in
many geological speculations it is taken for granted that the external crust
of the earth has been always growing thicker in consequence of the
accumulation, period after period, of sedimentary matter, as if the new
strata were not always produced at the expense of pre-existing rocks,
stratified or unstratified. By duly reflecting on the fact that all deposits of
mechanical origin imply the transportation from some other region, whether
contiguous or remote, of an equal amount of solid matter, we perceive that
the stony exterior of the planet must always have grown thinner in one
place, whenever, by accessions of new strata, it was acquiring thickness in
another.
It is well known that generally at the mouths of large rivers, deltas are
forming and the land is encroaching upon the sea; these deltas are
monuments of recent denudation and deposition; and it is obvious that if the
mud, sand, and gravel were taken from them and restored to the continents
they would fill up a large part of the gullies and valleys which are due to the
excavating and transporting power of torrents and rivers.
Alluvium.—Between the superficial covering of vegetable mould and
the subjacent rock there usually intervenes in every district a deposit of
loose gravel, sand, and mud, to which when it occurs in valleys the name of
alluvium has been popularly applied. The term is derived from alluvio, an
inundation, or alluo, to wash, because the pebbles and sand commonly
resemble those of a river’s bed or the mud and gravel washed over low
lands by a flood.
In the course of those changes in physical geography which may take
place during the gradual emergence of the bottom of the sea and its

conversion into dry land, any spot may either have been a sunken reef, or a
bay, or estuary, or sea-shore, or the bed of a river. The drainage, moreover,
may have been deranged again and again by earthquakes, during which
temporary lakes are caused by landslips, and partial deluges occasioned by
the bursting of the barriers of such lakes. For this reason it would be
unreasonable to hope that we should ever be able to account for all the
alluvial phenomena of each particular country, seeing that the causes of
their origin are so various. Besides, the last operations of water have a
tendency to disturb and confound together all pre-existing alluviums. Hence
we are always in danger of regarding as the work of a single era, and the
effect of one cause, what has in reality been the result of a variety of distinct
agents, during a long succession of geological epochs. Much useful
instruction may therefore be gained from the exploration of a country like
Auvergne, where the superficial gravel of very different eras happens to
have been preserved and kept separate by sheets of lava, which were poured
out one after the other at periods when the denudation, and probably the
upheaval, of rocks were in progress. That region had already acquired in
some degree its present configuration before any volcanoes were in activity,
and before any igneous matter was superimposed upon the granitic and
fossiliferous formations. The pebbles therefore in the older gravels are
exclusively constituted of granite and other aboriginal rocks; and
afterwards, when volcanic vents burst forth into eruption, those earlier
alluviums were covered by streams of lava, which protected them from
intermixture with gravel of subsequent date. In the course of ages, a new
system of valleys was excavated, so that the rivers ran at lower levels than
those at which the first alluviums and sheets of lava were formed. When,
therefore, fresh eruptions gave rise to new lava, the melted matter was
poured out over lower grounds; and the gravel of these plains differed from
the first or upland alluvium, by containing in it rounded fragments of
various volcanic rocks, and often fossil bones belonging to species of land
animals different from those which had previously flourished in the same
country and been buried in older gravels.

The annexed drawing (Fig. 81) will explain the different heights at which
beds of lava and gravel, each distinct from the other in composition and
age, are observed, some on the flat tops of hills, 700 or 800 feet high, others
on the slope of the same hills, and the newest of all in the channel of the
existing river where there is usually gravel alone, although in some cases a
narrow strip of solid lava shares the bottom of the valley with the river.
The proportion of extinct species of quadrupeds is more numerous in the
fossil remains of the gravel No. 1 than in that indicated as No. 2; and in No.
3 they agree more closely, sometimes entirely, with those of the existing
fauna. The usual absence or rarity of organic remains in beds of loose
gravel and sand is partly owing to the friction which originally ground
down the rocks into small fragments, and partly to the porous nature of
alluvium, which allows the free percolation through it of rain-water, and
promotes the decomposition and removal of fossil remains.
The loose transported matter on the surface of a large part of the land
now existing in the temperate and arctic regions of the northern hemisphere,
must be regarded as being in a somewhat exceptional state, in consequence
of the important part which ice has played in comparatively modern
geological times. This subject will be more specially alluded to when we
describe, in the eleventh chapter, the deposits called “glacial.”
Denuding Power of Rivers affected by Rise or Fall of Land.—It has
long been a matter of common observation that most rivers are now cutting
their channels through alluvial deposits of greater depth and extent than
could ever have been formed by the present streams. From this fact it has
been inferred that rivers in general have grown smaller, or become less
liable to be flooded than formerly. It may be true that in the history of
almost every country the rivers have been both larger and smaller than they
are at the present moment. For the rainfall in particular regions varies
according to climate and physical geography, and is especially governed by
the elevation of the land above the sea, or its distance from it and other
conditions equally fluctuating in the course of time. But the phenomenon

alluded to may sometimes be accounted for by oscillations in the level of
the land, experienced since the existing valleys originated, even where no
marked diminution in the quantity of rain and in the size of the rivers has
occurred.
We know that many large areas of land are rising and others sinking, and
unless it could be assumed that both the upward and downward movements
are everywhere uniform, many of the existing hydrographical basins ought
to have the appearance of having been temporary lakes first filled with
fluviatile strata and then partially re-excavated.
Suppose, for example, part of a continent, comprising within it a large
hydrographical basin like that of the Mississippi, to subside several inches
or feet in a century, as the west coast of Greenland, extending 600 miles
north and south, has been sinking for three or four centuries, between the
latitudes 60° and 69° N.[1] It will rarely happen that the rate of subsidence
will be everywhere equal, and in many cases the amount of depression in
the interior will regularly exceed that of the region nearer the sea.
Whenever this happens, the fall of the waters flowing from the upland
country will be diminished, and each tributary stream will have less power
to carry its sand and sediment into the main river, and the main river less
power to convey its annual burden of transported matter to the sea. All the
rivers, therefore, will proceed to fill up partially their ancient channels, and,
during frequent inundations, will raise their alluvial plains by new deposits.
If then the same area of land be again upheaved to its former height, the
fall, and consequently the velocity, of every river will begin to augment.
Each of them will be less given to overflow its alluvial plain; and their
power of carrying earthy matter seaward, and of scouring out and
deepening their channels, will be sustained till, after a lapse of many
thousand years, each of them has eroded a new channel or valley through a
fluviatile formation of comparatively modern date. The surface of what was
once the river-plain at the period of greatest depression, will then remain
fringing the valley-sides in the form of a terrace apparently flat, but in
reality sloping down with the general inclination of the river. Everywhere
this terrace will present cliffs of gravel and sand, facing the river. That such
a series of movements has actually taken place in the main valley of the
Mississippi and in its tributary valleys during oscillations of level, I have
endeavoured to show in my description of that country;[2] and the fresh-
water shells of existing species and bones of land quadrupeds, partly of

extinct races, preserved in the terraces of fluviatile origin, attest the
exclusion of the sea during the whole process of filling up and partial re-
excavation.
Littoral Denudation.—Part of the action of the waves between high and
low watermark must be included in subaërial denudation, more especially
as the undermining of cliffs by the waves is facilitated by land-springs, and
these often lead to the sliding down of great masses of land into the sea.
Along our coasts we find numerous submerged forests, only visible at low
water, having the trunks of the trees erect and their roots attached to them
and still spreading through the ancient soil as when they were living. They
occur in too many places, and sometimes at too great a depth, to be
explained by a mere change in the level of the tides, although as the coasts
waste away and alter in shape, the height to which the tides rise and fall is
always varying, and the level of high tide at any given point may, in the
course of many ages, differ by several feet or even fathoms. It is this
fluctuation in the height of the tides, and the erosion and destruction of the
sea-coast by the waves, that makes it exceedingly difficult for us in a few
centuries, or even perhaps in a few thousand years, to determine whether
there is a change by subterranean movement in the relative level of sea and
land.
We often behold, as on the coasts of Devonshire and Pembrokeshire,
facts which appear to lead to opposite conclusions. In one place a raised
beach with marine littoral shells, and in another immediately adjoining a
submerged forest. These phenomena indicate oscillations of level, and as
the movements are very gradual, they must give repeated opportunities to
the breakers to denude the land which is thus again and again exposed to
their fury, although it is evident that the submergence is sometimes effected
in such a manner as to allow the trees which border the coast not to be
carried away.
Inland Sea-cliffs.—In countries where hard limestone rocks abound,
inland cliffs have often retained faithfully for ages the characters which
they acquired when they constituted the boundary of land and sea. Thus, in
the Morea, no less than three or even four ranges of cliffs are well-
preserved, rising one above the other at different distances from the actual
shore, the summit of the highest and oldest occasionally attaining 1000 feet
in elevation. A consolidated beach with marine shells is usually found at the

base of each cliff, and a line of littoral caverns. These ranges of cliff
probably imply pauses in the process of upheaval when the waves and
currents had time to undermine and clear away considerable masses of rock.
But the beginner should be warned not to expect to find evidence of the
former sojourn of the sea on all those lands which we are nevertheless sure
have been submerged at periods comparatively modern; for notwithstanding
the enduring nature of the marks left by littoral action on some rocks,
especially limestones, we can by no means detect sea-beaches and inland
cliffs everywhere. On the contrary, they are, upon the whole, extremely
partial, and are often entirely wanting in districts composed of argillaceous
and sandy formations, which must, nevertheless, have been upheaved at the
same time, and by the same intermittent movements, as the adjoining harder
rocks.
Escarpments.—Besides the inland cliffs above alluded to which mark
the ancient limits of the sea, there are other abrupt terminations of rocks of
various kinds which resemble sea-cliffs, but which have in reality been due
to subaërial denudation. These have been called “escarpments,” a term
which it is useful to confine to the outcrop of particular formations having a
scarped outline, as distinct from cliffs due to marine action.
I formerly supposed that the steep line of cliff-like slopes seen along the
outcrop of the chalk, when we follow the edge of the North or South
Downs, was due to marine action; but Professor Ramsay has shown[3] that
the present outline of the physical geography is more in favour of the idea
of the escarpments having been due to gradual waste since the rocks were
exposed in the atmosphere to the action of rain and rivers.
Mr. Whittaker has given a good summary of the grounds for ascribing
these apparent sea-cliffs to waste in the open air. 1. There is an absence of
all signs of ancient sea-beaches or littoral deposits at the base of the
escarpment. 2. Great inequality is observed in the level of the base line. 3.
The escarpments do not intersect, like sea-cliffs, a series of distinct rocks,
but are always confined to the boundary-line of the same formation. 4.
There are sometimes different contiguous and parallel escarpments—those,
for example, of the greensand and chalk—which are so near each other, and
occasionally so similar in altitude, that we cannot imagine any existing
archipelago if converted into dry land to present a like outline.

The above theory is by no means inconsistent with the opinion that the
limits of the outcrop of the chalk and greensand which the escarpments now
follow, were originally determined by marine denudation. When the south-
east of England last emerged from beneath the level of the sea, it was acted
upon, no doubt, by the tide, waves, and currents, and the chalk would form
from the first a mass projecting above the more destructible clay called
Gault. Still the present escarpments so much resembling sea-cliffs have no
doubt, for reasons above stated, derived their most characteristic features
subsequently to emergence from subaërial waste by rain and rivers.
Submarine Denudation.—When we attempt to estimate the amount of
submarine denudation, we become sensible of the disadvantage under
which we labour from our habitual incapacity of observing the action of
marine currents on the bed of the sea. We know that the agitation of the
waves, even during storms, diminishes at a rapid rate, so as to become very
insignificant at the depth of a few fathoms, and is quite imperceptible at the
depth of about sixteen fathoms; but when large bodies of water are
transferred by a current from one part of the ocean to another, they are
known to maintain at great depths such a velocity as must enable them to
remove the finer, and sometimes even the coarser, materials of the rocks
over which they flow. As the Mississippi when more than 150 feet deep can
keep open its channel and even carry down gravel and sand to its delta, the
surface velocity being not more than two or three miles an hour, so a
gigantic current, like the Gulf Stream, equal in volume to many hundred
Mississippis, and having in parts a surface velocity of more than three
miles, may act as a propelling and abrading power at still greater depths.
But the efficacy of the sea as a denuding agent, geologically considered, is
not dependent on the power of currents to preserve at great depths a
velocity sufficient to remove sand and mud, because, even where the
deposition or removal of sediment is not in progress, the depth of water
does not remain constant throughout geological time. Every page of the
geological record proves to us that the relative levels of land and sea, and
the position of the ocean and of continents and islands, has been always
varying, and we may feel sure that some portions of the submarine area are
now rising and others sinking. The force of tidal and other currents and of
the waves during storms is sufficient to prevent the emergence of many
lands, even though they may be undergoing continual upheaval. It is not an
uncommon error to imagine that the waste of sea-cliffs affords the measure

of the amount of marine denudation of which it probably constitutes an
insignificant portion.
Dogger-bank.—That great shoal called the Dogger-bank, about sixty
miles east of the coast of Northumberland, and occupying an area about as
large as Wales, has nowhere a depth of more than ninety feet, and in its
shallower parts is less than forty feet under water. It might contribute
towards the safety of the navigation of our seas to form an artificial island,
and to erect a light-house on this bank; but no engineer would be rash
enough to attempt it, as he would feel sure that the ocean in the first heavy
gale would sweep it away as readily as it does every temporary shoal that
accumulates from time to time around a sunk vessel on the same bank.[4]
No observed geographical changes in historical times entitle us to assume
that where upheaval may be in progress it proceeds at a rapid rate. Three or
four feet rather than as many yards in a century may probably be as much as
we can reckon upon in our speculations; and if such be the case, the
continuance of the upward movement might easily be counteracted by the
denuding force of such currents aided by such waves as, during a gale, are
known to prevail in the German Ocean. What parts of the bed of the ocean
are stationary at present, and what areas may be rising or sinking, is a
matter of which we are very ignorant, as the taking of accurate soundings is
but of recent date.
Newfoundland Bank.—The great bank of Newfoundland may be
compared in size to the whole of England. This part of the bottom of the
Atlantic is surrounded on three sides by a rapidly deepening ocean, the bank
itself being from twenty to fifty fathoms (or from 120 to 300 feet) under
water. We are unable to determine by the comparison of different charts
made at distant periods, whether it is undergoing any change of level, but if
it be gradually rising we cannot anticipate on that account that it will
become land, because the breakers in an open sea would exercise a
prodigious force even on solid rock brought up to within a few yards of the
surface. We know, for example, that when a new volcanic island rose in the
Mediterranean in 1831, the waves were capable in a few years of reducing
it to a sunken rock.
In the same way currents which flow over the Newfoundland bank a
great part of the year at the rate of two miles an hour, and are known to
retain a considerable velocity to near the bottom, may carry away all loose

sand and mud, and make the emergence of the shoal impossible, in spite of
the accessions of mud, sand, and boulders derived occasionally from
melting icebergs which, coming from the northern glaciers, are frequently
stranded on various parts of the bank. They must often leave at the bottom
large erratic blocks which the marine currents may be incapable of moving,
but the same rocky fragments may be made to sink by the undermining of
beds consisting of finer matter on which the blocks and gravel repose. In
this way gravel and boulders may continue to overspread a submarine
bottom after the latter has been lowered for hundreds of feet, the surface
never having been able to emerge and become land. It is by no means
improbable that the annual removal of an average thickness of half an inch
of rock might counteract the ordinary upheaval which large submarine areas
are undergoing; and the real enigma which the geologist has to solve is not
the extensive denudation of the white chalk or of our tertiary sands and
clays, but the fact that such incoherent materials have ever succeeded in
lifting up their heads above water in an open sea. Why were they not swept
away during storms into some adjoining abysses, the highest parts of each
shoal being always planed off down to the depth of a few fathoms? The
hardness and toughness of some rocks already exposed to windward and
acting as breakwaters may perhaps have assisted; nor must we forget the
protection afforded by a dense and unbroken covering of barnacles, limpets,
and other creatures which flourish most between high and low water and
shelter some newly risen coasts from the waves.
[1] Principles of Geology 7th ed., p. 506; 10th ed., vol. ii, p. 196.

[2] Second Visit to the United States, vol. i, chap. xxxiv.

[3] Physical Geography and Geology of Great Britain, p. 78, 1864.

[4] Principles, 10th ed., vol. i, p. 569.

CHAPTER VII.
JOINT ACTION OF DENUDATION, UPHEAVAL,
AND SUBSIDENCE IN REMODELLING THE
EARTH’S CRUST.

How we obtain an Insight at the Surface, of the Arrangement
of Rocks at great Depths. — Why the Height of the
successive Strata in a given Region is so disproportionate to
their Thickness. — Computation of the average annual
Amount of subaërial Denudation. — Antagonism of
Volcanic Force to the Levelling Power of running Water. —
How far the Transfer of Sediment from the Land to a
neighbouring Sea-bottom may affect Subterranean
Movements. — Permanence of Continental and Oceanic
Areas.

How we obtain an Insight at the Surface, of the Arrangement of
Rocks at Great Depths.— The reader has been already informed that, in
the structure of the earth’s crust, we often find proofs of the direct
superposition of marine to fresh-water strata, and also evidence of the
alternation of deep-sea and shallow-water formations. In order to explain
how such a series of rocks could be made to form our present continents
and islands, we have not only to assume that there have been alternate
upward and downward movements of great vertical extent, but that the
upheaval in the areas which we at present inhabit has, in later geological
times, sufficiently predominated over subsidence to cause these portions of
the earth’s crust to be land instead of sea. The sinking down of a delta
beneath the sea-level may cause strata of fluviatile or even terrestrial origin,
such as peat with trees proper to marshes, to be covered by deposits of

deep-sea origin. There is also no end to the thickness of mud and sand
which may accumulate in shallow water, provided that fresh sediment is
brought down from the wasting land at a rate corresponding to that of the
sinking of the bed of the sea. The latter, again, may sometimes sink so fast
that the earthy matter, being intercepted in some new landward depression,
may never reach its former resting-place, where, the water becoming clear
may favour the growth of shells and corals, and calcareous rocks of organic
origin may thus be superimposed on mechanical deposits.
The succession of strata here alluded to would be consistent with the
occurrence of gradual downward and upward movements of the land and
bed of the sea without any disturbance of the horizontality of the several
formations. But the arrangement of rocks composing the earth’s crust
differs materially from that which would result from a mere series of
vertical movements. Had the volcanic forces been confined to such
movements, and had the stratified rocks been first formed beneath the sea
and then raised above it, without any lateral compression, the geologist
would never have obtained an insight into the monuments of various ages,
some of extremely remote antiquity.
What we have said in Chapter V of dip and strike, of the folding and
inversion of strata, of anticlinal and synclinal flexures, and in Chapter VI of
denudation at different periods, whether subaërial or submarine, must be
understood before the student can comprehend what may at first seem to
him an anomaly, but which it is his business particularly to understand. I
allude to the small height above the level of the sea attained by strata often
many miles in thickness, and about the chronological succession of which,
in one and the same region, there is no doubt whatever. Had stratified rocks
in general remained horizontal, the waves of the sea would have been
enabled during oscillations of level to plane off entirely the uppermost beds
as they rose or sank during the emergence or submergence of the land. But
the occurrence of a series of formations of widely different ages, all
remaining horizontal and in conformable stratification, is exceptional, and
for this reason the total annihilation of the uppermost strata has rarely taken
place. We owe, indeed, to the side way movements of lateral compression
those anticlinal and synclinal curves of the beds already described (Fig. 55),
which, together with denudation, subaërial and submarine, enable us to
investigate the structure of the earth’s crust many miles below those points
which the miner can reach. I have already shown in Fig. 56, how, at St.

Abb’s Head, a series of strata of indefinite thickness may become vertical,
and then denuded, so that the edges of the beds alone shall be exposed to
view, the altitude of the upheaved ridges being reduced to a moderate height
above the sea-level; and it may be observed that although the incumbent
strata of Old Red Sandstone are in that place nearly horizontal, yet these
same newer beds will in other places be found so folded as to present
vertical strata, the edges of which are abruptly cut off, as in 2, 3, 4 on the
right-hand side of the diagram, Fig. 55.
Why the Height of the Successive Strata in a given Region is so
Disproportionate to their Thickness.—We cannot too distinctly bear in
mind how dependent we are on the joint action of the volcanic and aqueous
forces, the one in disturbing the original position of rocks, and the other in
destroying large portions of them, for our power of consulting the different
pages and volumes of those stony records of which the crust of the globe is
composed. Why, it may be asked, if the ancient bed of the sea has been in
many regions uplifted to the height of two or three miles, and sometimes
twice that altitude, and if it can be proved that some single formations are of
themselves two or three miles thick, do we so often find several important
groups resting one upon the other, yet attaining only the height of a few
hundred feet above the level of the sea?
The American geologists, after carefully studying the Allegheny or
Appalachian mountains, have ascertained that the older fossiliferous rocks
of that chain (from the Silurian to the Carboniferous inclusive) are not less
than 42,000 feet thick, and if they were now superimposed on each other in
the order in which they were thrown down, they ought to equal in height the
Himalayas with the Alps piled upon them. Yet they rarely reach an altitude
of 5000 feet, and their loftiest peaks are no more than 7000 feet high. The
Carboniferous strata forming the highest member of the series, and
containing beds of coal, can be shown to be of shallow-water origin, or
even sometimes to have originated in swamps in the open air. But what is
more surprising, the lowest part of this great Palæozoic series, instead of
having been thrown down at the bottom of an abyss more than 40,000 feet
deep, consists of sediment (the Potsdam sandstone), evidently spread out on
the bottom of a shallow sea, on which ripple-marked sands were
occasionally formed. This vast thickness of 40,000 feet is not obtained by
adding together the maximum density attained by each formation in distant
parts of the chain, but by measuring the successive groups as they are

exposed in a very limited area, and where the denuded edges of the vertical
strata forming the parallel folds alluded to at page 87 “crop out” at the
surface. Our attention has been called by Mr. James Hall, Palæontologist of
New York, to the fact that these Palæozoic rocks of the Appalachian chain,
which are of such enormous density, where they are almost entirely of
mechanical origin, thin out gradually as they are traced to the westward,
where evidently the contemporaneous seas allowed organic rocks to be
formed by corals, echinoderms, and encrinites in clearer water, and where,
although the same successive periods are represented, the total mass of
strata from the Silurian to the Carboniferous, instead of being 40,000 is
only 4000 feet thick.
A like phenomenon is exhibited in every mountainous country, as, for
example, in the European Alps; but we need not go farther than the north of
England for its illustration. Thus in Lancashire and central England the
thickness of the Carboniferous formation, including the Millstone Grit and
Yoredale beds, is computed to be more than 18,000 feet; to this we may add
the Mountain Limestone, at least 2000 feet in thickness, and the overlying
Permian and Triassic formations, 3000 or 4000 feet thick. How then does it
happen that the loftiest hills of Yorkshire and Lancashire, instead of being
24,000 feet high, never rise above 3000 feet? For here, as before pointed
out in the Alleghenies, all the great thicknesses are sometimes found in
close approximation and in a region only a few miles in diameter. It is true
that these same sets of strata do not preserve their full force when followed
for indefinite distances. Thus the 18,000 feet of Carboniferous grits and
shales in Lancashire, before alluded to, gradually thin out, as Mr. Hull has
shown, as they extend southward, by attenuation or original deficiency of
sediment, and not in consequence of subsequent denudation, so that when
we have followed them for about 100 miles into Leicestershire, they have
dwindled away to a thickness of only 3000 feet. In the same region the
Carboniferous limestone attains so unusual a thickness—namely, more than
4000 feet—as to appear to compensate in some measure for the deficiency
of contemporaneous sedimentary rock.[1]
It is admitted that when two formations are unconformable their fossil
remains almost always differ considerably. The break in the continuity of
the organic forms seems connected with a great lapse of time, and the same
interval has allowed extensive disturbance of the strata, and removal of
parts of them by denudation, to take place. The more we extend our

investigations the more numerous do the proofs of these breaks become,
and they extend to the most ancient rocks yet discovered. The oldest
examples yet brought to light in the British Isles are on the borders of
Rosshire and Sutherlandshire, and have been well described by Sir
Roderick Murchison, by whom their chronological relations were admirably
worked out, and proved to be very different from those which previous
observers had imagined them to be. I had an opportunity in the autumn of
1869 of verifying the splendid section given in Fig. 82 by climbing in a few
hours from the banks of Loch Assynt to the summit of the mountain called
Queenaig, 2673 feet high.
The formations 1, 2, 3, the Laurentian, Cambrian, and Silurian, to be
explained in Chapters XXV and XXVI, not only occur in succession in this
one mountain, but their unconformable junctions are distinctly exposed to
view.

To begin with the oldest set of rocks, No. 1; they consist chiefly of
hornblendic gneiss, and in the neighbouring Hebrides form whole islands,
attaining a thickness of thousands of feet, although they have suffered such
contortions and denudation that they seldom rise more than a few hundred
feet above the sea-level. In discordant stratification upon the edges of this
gneiss reposes No. 2, a group of conglomerate and purple sandstone
referable to the Cambrian (or Longmynd) formation, which can elsewhere
be shown to be characterised by its peculiar organic remains. On this again
rests No. 3, a lower member of the important group called Silurian, an
outlier of which, 3′, caps the summit of Queenaig, attesting the removal by
denudation of rocks of the same age, which once extended from the great
mass 3 to 3′. Although this rock now consists of solid quartz, it is clear that
in its original state it was formed of fine sand, perforated by numerous lob-
worms or annelids, which left their burrows in the shape of tubular hollows

Fig. 563 of Arenicolites), hundreds, nay thousands, of which I saw as I
ascended the mountain.

In Queenaig we only behold this single quartzose member of the Silurian
series, but in the neighbouring country (see Fig. 83) it is seen to the
eastward to be followed by limestones, 3a, and schists, 3b, presenting
numerous folds, and becoming more and more metamorphic and crystalline,
until at length, although very different in age and strike, they much
resemble in appearance the group No. 1. It is very seldom that in the same
country one continuous formation, such as the Silurian, is, as in this case,
more fossiliferous and less altered by volcanic heat in its older than in its
newer strata, and still more rare to find an underlying and unconformable
group like the Cambrian retaining its original condition of a conglomerate
and sandstone more perfectly than the overlying formation. Here also we
may remark in regard to the origin of these Cambrian rocks that they were
evidently produced at the expense of the underlying Laurentian, for the
rounded pebbles occurring in them are identical in composition and texture
with that crystalline gneiss which constitutes the contorted beds of the
inferior formation No. 1. When the reader has studied the chapter on
metamorphism, and has become aware how much modification by heat,
pressure, and chemical action is required before the conversion of
sedimentary into crystalline strata can be brought about, he will appreciate
the insight which we thus gain into the date of the changes which had
already been effected in the Laurentian rocks long before the Cambrian
pebbles of quartz and gneiss were derived from them. The Laurentian is
estimated by Sir William Logan to amount in Canada to 30,000 feet in
thickness. As to the Cambrian, it is supposed by Sir Roderick Murchison
that the fragment left in Sutherlandshire is about 3500 feet thick, and in
Wales and the borders of Shropshire this formation may equal 10,000 feet,
while the Silurian strata No. 3, difficult as it may be to measure them in

their various foldings to the eastward, where they have been invaded by
intrusive masses of granite, are supposed many times to surpass the
Cambrian in volume and density.
But although we are dealing here with stratified rocks, each of which
would be several miles in thickness, if they were fully represented, the
whole of them do not attain the elevation of a single mile above the level of
the sea.
Computation of the Average Annual Amount of Subaërial
Denudation.—The geology of the district above alluded to may assist our
imagination in conceiving the extent to which groups of ancient rocks, each
of which may in their turn have formed continents and oceanic basins, have
been disturbed, folded, and denuded even in the course of a few out of
many of those geological periods to which our imperfect records relate. It is
not easy for us to overestimate the effects which causes in every day action
must produce when the multiplying power of time is taken into account.
Attempts were made by Manfredi in 1736, and afterwards by Playfair in
1802, to calculate the time which it would require to enable the rivers to
deliver over the whole of the land into the basin of the ocean. The data were
at first too imperfect and vague to allow them even to approximate to safe
conclusions. But in our own time similar investigations have been renewed
with more prospect of success, the amount brought down by many large
rivers to the sea having been more accurately ascertained. Mr. Alfred Tylor,
in 1850, inferred that the quantity of detritus now being distributed over the
sea-bottom would, at the end of 10,000 years, cause an elevation of the sea-
level to the extent of at least three inches.[2] Subsequently Mr. Croll, in
1867, and again, with more exactness, in 1868, deduced from the latest
measurement of the sediment transported by European and American rivers
the rate of subaërial denudation to which the surface of large continents is
exposed, taking especially the hydrographical basin of the Mississippi as
affording the best available measure of the average waste of the land. The
conclusion arrived at in his able memoir,[3] was that the whole terrestrial
surface is denuded at the rate of one foot in 6000 years and this opinion was
simultaneously enforced by his fellow-labourer, Mr. Geikie, who, being
jointly engaged in the same line of inquiry, published a luminous essay on
the subject in 1868.

The student, by referring to my “Principles of Geology,”[4] may see that
Messrs. Humphrey and Abbot, during their survey of the Mississippi,
attempted to make accurate measurements of the proportion of sediment
carried down annually to the sea by that river, including not only the mud
held in suspension, but also the sand and gravel forced along the bottom.
It is evident that when we know the dimensions of the area which is
drained, and the annual quantity of earthy matter taken from it and borne
into the sea, we can affirm how much on an average has been removed from
the general surface in one year, and there seems no danger of our overrating
the mean rate of waste by selecting the Mississippi as our example, for that
river drains a country equal to more than half the continent of Europe,
extends through twenty degrees of latitude, and therefore through regions
enjoying a great variety of climate, and some of its tributaries descend from
mountains of great height. The Mississippi is also more likely to afford us a
fair test of ordinary denudation, because, unlike the St. Lawrence and its
tributaries, there are no great lakes in which the fluviatile sediment is
thrown down and arrested in its way to the sea. In striking a general average
we have to remember that there are large deserts in which there is scarcely
any rainfall, and tracts which are as rainless as parts of Peru, and these must
not be neglected as counterbalancing others, in the tropics, where the
quantity of rain is in excess. If then, argues Mr. Geikie, we assume that the
Mississippi is lowering the surface of the great basin which it drains at the
rate of one foot in 6000 years, 10 feet in 60,000 years, 100 feet in 600,000
years, and 1000 feet in 6,000,000 years, it would not require more than
about 4,500,000 years to wear away the whole of the North American
continent if its mean height is correctly estimated by Humboldt at 748 feet.
And if the mean height of all the land now above the sea throughout the
globe is 1000 feet, as some geographers believe, it would only require six
million years to subject a mass of rock equal in volume to the whole of the
land to the action of subaërial denudation. It may be objected that the
annual waste is partial, and not equally derived from the general surface of
the country, inasmuch as plains, water-sheds, and level ground at all heights
remain comparatively unaltered; but this, as Mr. Geikie has well pointed
out, does not affect our estimate of the sum total of denudation. The amount
remains the same, and if we allow too little for the loss from the surface of
table-lands we only increase the proportion of the loss sustained by the
sides and bottoms of the valleys, and vice versa.[5]

Antagonism of Volcanic Force to the Levelling Power of Running
Water.—In all these estimates it is assumed that the entire quantity of land
above the sea-level remains on an average undiminished in spite of annual
waste. Were it otherwise the subaërial denudation would be continually
lessened by the diminution of the height and dimensions of the land
exposed to waste. Unfortunately we have as yet no accurate data enabling
us to measure the action of that force by which the inequalities of the
surface of the earth’s crust may be restored, and the height of the continents
and depth of the seas made to continue unimpaired. I stated in 1830 in the
“Principles of Geology,”[6] that running water and volcanic action are two
antagonistic forces; the one labouring continually to reduce the whole of the
land to the level of the sea, the other to restore and maintain the inequalities
of the crust on which the very existence of islands and continents depends. I
stated, however, that when we endeavour to form some idea of the relation
of these destroying and renovating forces, we must always bear in mind that
it is not simply by upheaval that subterranean movements can counteract
the levelling force of running water. For whereas the transportation of
sediment from the land to the ocean would raise the general sea-level, the
subsidence of the sea-bottom, by increasing its capacity, would check this
rise and prevent the submergence of the land. I have, indeed, endeavoured
to show that unless we assume that there is, on the whole, more subsidence
than upheaval, we must suppose the diameter of the planet to be always
increasing, by that quantity of volcanic matter which is annually poured out
in the shape of lava or ashes, whether on the land or in the bed of the sea,
and which is derived from the interior of the earth. The abstraction of this
matter causes, no doubt, subterranean vacuities and a corresponding giving
way of the surface; if it were not so, the average density of parts of the
interior would be always lessening and the size of the planet increasing.[7]
Our inability to estimate the amount or direction of the movements due to
volcanic power by no means renders its efficacy as a land-preserving force
in past times a mere matter of conjecture. The student will see in Chapter
XXIV that we have proofs of Carboniferous forests hundreds of miles in
extent which grew on the lowlands or deltas near the sea, and which
subsided and gave place to other forests, until in some regions fluviatile and
shallow-water strata with occasional seams of coal were piled one over the
other, till they attained a thickness of many thousand feet. Such
accumulations, observed in Great Britain and America on opposite sides of

the Atlantic, imply the long-continued existence of land vegetation, and of
rivers draining a former continent placed where there is now deep sea.
It will be also seen in Chapter XXV that we have evidence of a rich
terrestrial flora, the Devonian, even more ancient than the Carboniferous;
while on the other hand, the later Triassic, Oolitic, Cretaceous, and
successive Tertiary periods have all supplied us with fossil plants, insects,
or terrestrial mammalia; showing that, in spite of great oscillations of level
and continued changes in the position of land and sea, the volcanic forces
have maintained a due proportion of dry land. We may appeal also to fresh-
water formations, such as the Purbeck and Wealden, to prove that in the
Oolitic and Neocomian eras there were rivers draining ancient lands in
Europe in times when we know that other spaces, now above water, were
submerged.
How far the Transfer of Sediment from the Land to a Neighbouring
Sea-bottom may affect Subterranean Movements.—Little as we
understand at present the laws which govern the distribution of volcanic
heat in the interior and crust of the globe, by which mountain chains, high
table-lands, and the abysses of the ocean are formed, it seems clear that this
heat is the prime mover on which all the grander features in the external
configuration of the planet depend.
It has been suggested that the stripping off by denudation of dense
masses from one part of a continent and the delivery of the same into the
bed of the ocean must have a decided effect in causing changes of
temperature in the earth’s crust below, or, in other words, in causing the
subterranean isothermals to shift their position. If this be so, one part of the
crust may be made to rise, and another to sink, by the expansion and
contraction of the rocks, of which the temperature is altered.
I cannot, at present, discuss this subject, of which I have treated more
fully elsewhere,[8] but may state here that I believe this transfer of sediment
to play a very subordinate part in modifying those movements on which the
configuration of the earth’s crust depends. In order that strata of shallow-
water origin should be able to attain a thickness of several thousand feet,
and so come to exert a considerable downward pressure, there must have
been first some independent and antecedent causes at work which have
given rise to the incipient shallow receptacle in which the sediment began
to accumulate. The same causes there continuing to depress the sea-bottom,

room would be made for fresh accessions of sediment, and it would only be
by a long repetition of the depositing process that the new matter could
acquire weight enough to affect the temperature of the rocks far below, so
as to increase or diminish their volume.
Permanence of Continental and Oceanic Areas.—If the thickness of
more than 40,000 feet of sedimentary strata before alluded to in the
Appalachians proves a preponderance of downward movements in
Palæozoic times in a district now forming the eastern border of North
America, it also proves, as before hinted, the continued existence and waste
of some neighbouring continent, probably formed of Laurentian rocks, and
situated where the Atlantic now prevails. Such an hypothesis would be in
perfect harmony with the conclusions forced upon us by the study of the
present configuration of our continents, and the relation of their height to
the depth of the oceanic basins; also to the considerable elevation and
extent sometimes reached by drift containing shells of recent species, and
still more by the fact of sedimentary strata, several thousand feet thick, as
those of central Sicily, or such as flank the Alps and Apennines, containing
fossil Mollusca sometimes almost wholly identical with species still living.
I have remarked elsewhere[9] that upward and downward movements of
1000 feet or more would turn much land into sea and sea into land in the
continental areas and their borders, whereas oscillations of equal magnitude
would have no corresponding effect in the bed of the ocean generally,
believed as it is to have a mean depth of 15,000 feet, and which, whether
this estimate be correct or not, is certainly of great profundity. Subaërial
denudation would not of itself lessen the area of the land, but would tend to
fill up with sediment seas of moderate depth adjoining the coast. The
coarser matter falls to the bottom near the shore in the first still water which
it reaches, and whenever the sea-bottom on which this matter has been
thrown is slightly elevated, it becomes land, and an upheaval of a thousand
feet causes it to attain the mean elevation of continents in general.
Suppose, therefore, we had ascertained that the triturating power of
subaërial denudation might in a given time—in three, or six, or a greater
number of millions of years—pulverise a volume of rock equal in
dimensions to all the present land, we might yet find, could we revisit the
earth at the end of such a period, that the continents occupied very much the
same position which they held before; we should find the rivers employed

in carrying down to the sea the very same mud, sand, and pebbles with
which they had been charged in our own time, the superficial alluvial matter
as well as a great thickness of sedimentary strata would inclose shells, all or
a great part of which we should recognise as specifically identical with
those already known to us as living. Every geologist is aware that great as
have been the geographical changes in the northern hemisphere since the
commencement of the Glacial Period, there having been submergence and
re-emergence of land to the extent of 1000 feet vertically, and in the
temperate latitudes great vicissitudes of climate, the marine mollusca have
not changed, and the same drift which had been carried down to the sea at
the beginning of the period is now undergoing a second transportation in the
same direction.
As when we have measured a fraction of time in an hour-glass we have
only to reverse the position of our chronometer and we make the same sand
measure over again the duration of a second equal period, so when the
volcanic force has remoulded the form of a continent and the adjoining sea-
bottom, the same materials are made to do duty a second time. It is true that
at each oscillation of level the solid rocks composing the original continent
suffer some fresh denudation, and do not remain unimpaired like the
wooden and glass framework of the hour-glass, still the wear and tear
suffered by the larger area exposed to subaërial denudation consists either
of loose drift or of sedimentary strata, which were thrown down in seas near
the land, and subsequently upraised, the same continents and oceanic basins
remaining in existence all the while.
From all that we know of the extreme slowness of the upward and
downward movements which bring about even slight geographical changes,
we may infer that it would require a long succession of geological periods
to cause the submarine and supramarine areas to change places, even if the
ascending movements in the one region and the descending in the other
were continuously in one direction. But we have only to appeal to the
structure of the Alps, where there are so many shallow and deep water
formations of various ages crowded into a limited area, to convince
ourselves that mountain chains are the result of great oscillations of level.
High land is not produced simply by uniform upheaval, but by a
predominance of elevatory over subsiding movements. Where the ocean is
extremely deep it is because the sinking of the bottom has been in excess, in
spite of interruptions by upheaval.

Yet persistent as may be the leading features of land and sea on the globe,
they are not immutable. Some of the finest mud is doubtless carried to
indefinite distances from the coast by marine currents, and we are taught by
deep-sea dredgings that in clear water at depths equalling the height of the
Alps organic beings may flourish, and their spoils slowly accumulate on the
bottom. We also occasionally obtain evidence that submarine volcanoes are
pouring out ashes and streams of lava in mid-ocean as well as on land (see
Principles, vol. ii, p. 64), and that wherever mountains like Etna, Vesuvius,
and the Canary Islands are now the site of eruptions, there are signs of
accompanying upheaval, by which beds of ashes full of recent marine shells
have been uplifted many hundred feet. We need not be surprised, therefore,
if we learn from geology that the continents and oceans were not always
placed where they now are, although the imagination may well be
overpowered when it endeavours to contemplate the quantity of time
required for such revolutions.
We shall have gained a great step if we can approximate to the number of
millions of years in which the average aqueous denudation going on upon
the land would convey seaward a quantity of matter equal to the average
volume of our continents, and this might give us a gauge of the minimum of
volcanic force necessary to counteract such levelling power of running
water; but to discover a relation between these great agencies and the rate at
which species of organic beings vary, is at present wholly beyond the reach
of our computation, though perhaps it may not prove eventually to
transcend the powers of man.
[1] Hull, Quart. Geol. Journ., vol. xxiv, p. 322, 1868.

[2] Tylor, Phil. Mag., 4th series, p. 268, 1850.

[3] Croll, Phil. Mag., 1868, p. 381.

[4] Vol. i, p. 442, 1867.

[5] Trans. Geol. Soc. Glasgow, vol. iii, p. 169.

[6] 1st ed., chap. x, p. 167, 1830; see also 10th ed., vol. i, chap. xv, p. 327, 1867.

[7] Principles, vol. ii, p. 237; also 1st ed., p. 447, 1830.

[8] Principles, vol. ii, p. 229, 1868.

[9] Principles, vol. i, p. 265, 1867.

CHAPTER VIII.
CHRONOLOGICAL CLASSIFICATION OF
ROCKS.

Aqueous, Plutonic, volcanic, and metamorphic Rocks
considered chronologically. — Terms Primary, Secondary,
and Tertiary; Palæozoic, Mesozoic, and Cainozoic
explained. — On the different Ages of the aqueous Rocks.
— Three principal Tests of relative Age: Superposition,
Mineral Character, and Fossils. — Change of Mineral
Character and Fossils in the same continuous Formation. —
Proofs that distinct Species of Animals and Plants have lived
at successive Periods. — Distinct Provinces of indigenous
Species. — Great Extent of single Provinces. — Similar
Laws prevailed at successive Geological Periods. —
Relative Importance of mineral and palæontological
Characters. — Test of Age by included Fragments. —
Frequent Absence of Strata of intervening Periods. —
Tabular Views of fossiliferous Strata.

Chronology of Rocks.— In the first chapter it was stated that the four
great classes of rocks, the aqueous, the volcanic, the Plutonic, and the
metamorphic, would each be considered not only in reference to their
mineral characters, and mode of origin, but also to their relative age. In
regard to the aqueous rocks, we have already seen that they are stratified,
that some are calcareous, others argillaceous or siliceous, some made up of
sand, others of pebbles; that some contain fresh-water, others marine fossils,
and so forth; but the student has still to learn which rocks, exhibiting some
or all of these characters, have originated at one period of the earth’s
history, and which at another.

To determine this point in reference to the fossiliferous formations is
more easy than in any other class, and it is therefore the most convenient
and natural method to begin by establishing a chronology for these strata,
and then to refer as far as possible to the same divisions, the several groups
of Plutonic, volcanic, and metamorphic rocks. Such a system of
classification is not only recommended by its greater clearness and facility
of application, but is also best fitted to strike the imagination by bringing
into one view the contemporaneous revolutions of the inorganic and organic
creations of former times. For the sedimentary formations are most readily
distinguished by the different species of fossil animals and plants which
they inclose, and of which one assemblage after another has flourished and
then disappeared from the earth in succession.
In the present work, therefore, the four great classes of rocks, the
aqueous, Plutonic, volcanic, and metamorphic, will form four parallel, or
nearly parallel, columns in one chronological table. They will be considered
as four sets of monuments relating to four contemporaneous, or nearly
contemporaneous, series of events. I shall endeavour, in a subsequent
chapter on the Plutonic rocks, to explain the manner in which certain
masses belonging to each of the four classes of rocks may have originated
simultaneously at every geological period, and how the earth’s crust may
have been continually remodelled, above and below, by aqueous and
igneous causes, from times indefinitely remote. In the same manner as
aqueous and fossiliferous strata are now formed in certain seas or lakes,
while in other places volcanic rocks break out at the surface, and are
connected with reservoirs of melted matter at vast depths in the bowels of
the earth, so, at every era of the past, fossiliferous deposits and superficial
igneous rocks were in progress contemporaneously with others of
subterranean and Plutonic origin, and some sedimentary strata were
exposed to heat, and made to assume a crystalline or metamorphic structure.
It can by no means be taken for granted, that during all these changes the
solid crust of the earth has been increasing in thickness. It has been shown,
that so far as aqueous action is concerned, the gain by fresh deposits, and
the loss by denudation, must at each period have been equal (see above,
Chap. VI, p. 96); and in like manner, in the inferior portion of the earth’s
crust, the acquisition of new crystalline rocks, at each successive era, may
merely have counterbalanced the loss sustained by the melting of materials
previously consolidated. As to the relative antiquity of the crystalline

foundations of the earth’s crust, when compared to the fossiliferous and
volcanic rocks which they support, I have already stated, in the first chapter,
that to pronounce an opinion on this matter is as difficult as at once to
decide which of the two, whether the foundations or superstructure of an
ancient city built on wooden piles may be the oldest. We have seen that, to
answer this question, we must first be prepared to say whether the work of
decay and restoration had gone on most rapidly above or below; whether
the average duration of the piles has exceeded that of the buildings, or the
contrary. So also in regard to the relative age of the superior and inferior
portions of the earth’s crust; we cannot hazard even a conjecture on this
point, until we know whether, upon an average, the power of water above,
or that of heat below, is most efficacious in giving new forms to solid
matter.
The early geologists gave to all the crystalline and non-fossiliferous
rocks the name of Primitive or Primary, under the idea that they were
formed anterior to the appearance of life upon the earth, while the aqueous
or fossiliferous strata were termed Secondary, and alluviums or other
superficial deposits, Tertiary. The meaning of these terms, has, however,
been gradually modified with advancing knowledge, and they are now used
to designate three great chronological divisions under which all geological
formations can be classed, each of them being characterised by the presence
of distinctive groups of organic remains rather than by any mechanical
peculiarities of the strata themselves. If, therefore, we retain the term
“primary,” it must not be held to designate a set of crystalline rocks some of
which have been proved to be even of Tertiary age, but must be applied to
all rocks older than the secondary formations. Some geologists, to avoid
misapprehension, have introduced the term Palæozoic for primary, from
palaion, “ancient,” and zoon, “an organic being,” still retaining the terms
secondary and tertiary; Mr. Phillips, for the sake of uniformity, has
proposed Mesozoic, for secondary, from mesos, “middle,” etc.; and
Cainozoic, for tertiary, from kainos, “recent,” etc.; but the terms primary,
secondary, and tertiary have the claim of priority in their favour, and are of
corresponding value.
It may perhaps be suggested that some metamorphic strata, and some
granites, may be anterior in date to the oldest of the primary fossiliferous
rocks. This opinion is doubtless true, and will be discussed in future
chapters; but I may here observe, that when we arrange the four classes of

rocks in four parallel columns in one table of chronology, it is by no means
assumed that these columns are all of equal length; one may begin at an
earlier period than the rest, and another may come down to a later point of
time, and we may not be yet acquainted with the most ancient of the
primary fossiliferous beds, or with the newest of the hypogene.
For reasons already stated, I proceed first to treat of the aqueous or
fossiliferous formations considered in chronological order or in relation to
the different periods at which they have been deposited.
There are three principal tests by which we determine the age of a given
set of strata; first, superposition; secondly, mineral character; and, thirdly,
organic remains. Some aid can occasionally be derived from a fourth kind
of proof, namely, the fact of one deposit including in it fragments of a pre-
existing rock, by which the relative ages of the two may, even in the
absence of all other evidence, be determined.
Superposition.—The first and principal test of the age of one aqueous
deposit, as compared to another, is relative position. It has been already
stated, that, where strata are horizontal, the bed which lies uppermost is the
newest of the whole, and that which lies at the bottom the most ancient. So,
of a series of sedimentary formations, they are like volumes of history, in
which each writer has recorded the annals of his own times, and then laid
down the book, with the last written page uppermost, upon the volume in
which the events of the era immediately preceding were commemorated. In
this manner a lofty pile of chronicles is at length accumulated; and they are
so arranged as to indicate, by their position alone, the order in which the
events recorded in them have occurred.
In regard to the crust of the earth, however, there are some regions where,
as the student has already been informed, the beds have been disturbed, and
sometimes extensively thrown over and turned upside down. (See p. 73, p.
87.) But an experienced geologist can rarely be deceived by these
exceptional cases. When he finds that the strata are fractured, curved,
inclined, or vertical, he knows that the original order of superposition must
be doubtful, and he then endeavours to find sections in some neighbouring
district where the strata are horizontal, or only slightly inclined. Here, the
true order of sequence of the entire series of deposits being ascertained, a
key is furnished for settling the chronology of those strata where the
displacement is extreme.

Mineral Character.—The same rocks may often be observed to retain
for miles, or even hundreds of miles, the same mineral peculiarities, if we
follow the planes of stratification, or trace the beds, if they be undisturbed,
in a horizontal direction. But if we pursue them vertically, or in any
direction transverse to the planes of stratification, this uniformity ceases
almost immediately. In that case we can scarcely ever penetrate a stratified
mass for a few hundred yards without beholding a succession of extremely
dissimilar rocks, some of fine, others of coarse grain, some of mechanical,
others of chemical origin; some calcareous, others argillaceous, and others
siliceous. These phenomena lead to the conclusion that rivers and currents
have dispersed the same sediment over wide areas at one period, but at
successive periods have been charged, in the same region, with very
different kinds of matter. The first observers were so astonished at the vast
spaces over which they were able to follow the same homogeneous rocks in
a horizontal direction, that they came hastily to the opinion, that the whole
globe had been environed by a succession of distinct aqueous formations,
disposed round the nucleus of the planet, like the concentric coats of an
onion. But, although, in fact, some formations may be continuous over
districts as large as half of Europe, or even more, yet most of them either
terminate wholly within narrower limits, or soon change their lithological
character. Sometimes they thin out gradually, as if the supply of sediment
had failed in that direction, or they come abruptly to an end, as if we had
arrived at the borders of the ancient sea or lake which served as their
receptacle. It no less frequently happens that they vary in mineral aspect
and composition, as we pursue them horizontally. For example, we trace a
limestone for a hundred miles, until it becomes more arenaceous, and
finally passes into sand, or sandstone. We may then follow this sandstone,
already proved by its continuity to be of the same age, throughout another
district a hundred miles or more in length.
Organic Remains.—This character must be used as a criterion of the age
of a formation, or of the contemporaneous origin of two deposits in distant
places, under very much the same restrictions as the test of mineral
composition.
First, the same fossils may be traced over wide regions, if we examine
strata in the direction of their planes, although by no means for indefinite
distances. Secondly, while the same fossils prevail in a particular set of
strata for hundreds of miles in a horizontal direction, we seldom meet with

the same remains for many fathoms, and very rarely for several hundred
yards, in a vertical line, or a line transverse to the strata. This fact has now
been verified in almost all parts of the globe, and has led to a conviction
that at successive periods of the past, the same area of land and water has
been inhabited by species of animals and plants even more distinct than
those which now people the antipodes, or which now co-exist in the arctic,
temperate, and tropical zones. It appears that from the remotest periods
there has been ever a coming in of new organic forms, and an extinction of
those which pre-existed on the earth; some species having endured for a
longer, others for a shorter, time; while none have ever reappeared after
once dying out. The law which has governed the succession of species,
whether we adopt or reject the theory of transmutation, seems to be
expressed in the verse of the poet:—
Natura il fece, e poi ruppe la stampa. ARIOSTO.
Nature made him, and then broke the die.

And this circumstance it is, which confers on fossils their highest value as
chronological tests, giving to each of them, in the eyes of the geologist, that
authority which belongs to contemporary medals in history.
The same cannot be said of each peculiar variety of rock; for some of
these, as red marl and red sandstone, for example, may occur at once at the
top, bottom, and middle of the entire sedimentary series; exhibiting in each
position so perfect an identity of mineral aspect as to be undistinguishable.
Such exact repetitions, however, of the same mixtures of sediment have not
often been produced, at distant periods, in precisely the same parts of the
globe; and even where this has happened, we are seldom in any danger of
confounding together the monuments of remote eras, when we have studied
their imbedded fossils and their relative position.
Zoological Provinces.—It was remarked that the same species of organic
remains cannot be traced horizontally, or in the direction of the planes of
stratifications for indefinite distances. This might have been expected from
analogy; for when we inquire into the present distribution of living beings,
we find that the habitable surface of the sea and land may be divided into a
considerable number of distinct provinces, each peopled by a peculiar
assemblage of animals and plants. In the “Principles of Geology,” I have
endeavoured to point out the extent and probable origin of these separate
divisions; and it was shown that climate is only one of many causes on

which they depend, and that difference of longitude as well as latitude is
generally accompanied by a dissimilarity of indigenous species.
As different seas, therefore, and lakes are inhabited, at the same period,
by different aquatic animals and plants, and as the lands adjoining these
may be peopled by distinct terrestrial species, it follows that distinct fossils
will be imbedded in contemporaneous deposits. If it were otherwise—if the
same species abounded in every climate, or in every part of the globe
where, so far as we can discover, a corresponding temperature and other
conditions favourable to their existence are found—the identification of
mineral masses of the same age, by means of their included organic
contents, would be a matter of still greater certainty.
Nevertheless, the extent of some single zoological provinces, especially
those of marine animals, is very great; and our geological researches have
proved that the same laws prevailed at remote periods; for the fossils are
often identical throughout wide spaces, and in detached deposits, consisting
of rocks varying entirely in their mineral nature.
The doctrine here laid down will be more readily understood, if we
reflect on what is now going on in the Mediterranean. That entire sea may
be considered as one zoological province; for although certain species of
testacea and zoophytes may be very local, and each region has probably
some species peculiar to it, still a considerable number are common to the
whole Mediterranean. If, therefore, at some future period, the bed of this
inland sea should be converted into land, the geologist might be enabled, by
reference to organic remains, to prove the contemporaneous origin of
various mineral masses scattered over a space equal in area to half of
Europe.
Deposits, for example, are well known to be now in progress in this sea
in the deltas of the Po, Rhone, Nile, and other rivers, which differ as greatly
from each other in the nature of their sediment as does the composition of
the mountains which their drain. There are also other quarters of the
Mediterranean, as off the coast of Campania, or near the base of Etna, in
Sicily, or in the Grecian Archipelago, where another class of rocks is now
forming; where showers of volcanic ashes occasionally fall into the sea, and
streams of lava overflow its bottom; and where, in the intervals between
volcanic eruptions, beds of sand and clay are frequently derived from the
waste of cliffs, or the turbid waters of rivers. Limestones, moreover, such as

the Italian travertins, are here and there precipitated from the waters of
mineral springs, some of which rise up from the bottom of the sea. In all
these detached formations, so diversified in their lithological characters, the
remains of the same shells, corals, crustacea, and fish are becoming
inclosed; or, at least, a sufficient number must be common to the different
localities to enable the zoologist to refer them all to one contemporaneous
assemblage of species.
There are, however, certain combinations of geographical circumstances
which cause distinct provinces of animals and plants to be separated from
each other by very narrow limits; and hence it must happen that strata will
be sometimes formed in contiguous regions, differing widely both in
mineral contents and organic remains. Thus, for example, the testacea,
zoophytes, and fish of the Red Sea are, as a group, extremely distinct from
those inhabiting the adjoining parts of the Mediterranean, although the two
seas are separated only by the narrow isthmus of Suez. Calcareous
formations have accumulated on a great scale in the Red Sea in modern
times, and fossil shells of existing species are well preserved therein; and
we know that at the mouth of the Nile large deposits of mud are amassed,
including the remains of Mediterranean species. It follows, therefore, that if
at some future period the bed of the Red Sea should be laid dry, the
geologist might experience great difficulties in endeavouring to ascertain
the relative age of these formations, which, although dissimilar both in
organic and mineral characters, were of synchronous origin.
But, on the other hand, we must not forget that the north-western shores
of the Arabian Gulf, the plains of Egypt, and the Isthmus of Suez, are all
parts of one province of terrestrial species. Small streams, therefore,
occasional land- floods, and those winds which drift clouds of sand along
the deserts, might carry down into the Red Sea the same shells of fluviatile
and land testacea which the Nile is sweeping into its delta, together with
some remains of terrestrial plants and the bones of quadrupeds, whereby the
groups of strata before alluded to might, notwithstanding the discrepancy of
their mineral composition and marine organic fossils, be shown to have
belonged to the same epoch.
Yet, while rivers may thus carry down the same fluviatile and terrestrial
spoils into two or more seas inhabited by different marine species, it will
much more frequently happen that the coexistence of terrestrial species of

distinct zoological and botanical provinces will be proved by the identity of
the marine beings which inhabited the intervening space. Thus, for
example, the land quadrupeds and shells of the valley of the Mississippi, of
central America, and of the West India islands differ very considerably, yet
their remains are all washed down by rivers flowing from these three
zoological provinces into the Gulf of Mexico.
In some parts of the globe, at the present period, the line of demarkation
between distinct provinces of animals and plants is not very strongly
marked, especially where the change is determined by temperature, as it is
in seas extending from the temperate to the tropical zone, or from the
temperate to the arctic regions. Here a gradual passage takes place from one
set of species to another. In like manner the geologist, in studying particular
formations of remote periods, has sometimes been able to trace the
gradation from one ancient province to another, by observing carefully the
fossils of all the intermediate places. His success in thus acquiring a
knowledge of the zoological or botanical geography of very distant eras has
been mainly owing to this circumstance, that the mineral character has no
tendency to be affected by climate. A large river may convey yellow or red
mud into some part of the ocean, where it may be dispersed by a current
over an area several hundred leagues in length, so as to pass from the
tropics into the temperate zone. If the bottom of the sea be afterwards
upraised, the organic remains imbedded in such yellow or red strata may
indicate the different animals or plants which once inhabited at the same
time the temperate and equatorial regions.
It may be true, as a general rule, that groups of the same species of
animals and plants may extend over wider areas than deposits of
homogeneous composition; and if so, palæontological characters will be of
more importance in geological classification than the test of mineral
composition; but it is idle to discuss the relative value of these tests, as the
aid of both is indispensable, and it fortunately happens, that where the one
criterion fails, we can often avail ourselves of the other.
Test by included Fragments of older Rocks.—It was stated, that proof
may sometimes be obtained of the relative date of two formations by
fragments of an older rock being included in a newer one. This evidence
may sometimes be of great use, where a geologist is at a loss to determine
the relative age of two formations from want of clear sections exhibiting

their true order of position, or because the strata of each group are vertical.
In such cases we sometimes discover that the more modern rock has been in
part derived from the degradation of the older. Thus, for example, we may
find chalk in one part of a country, and in another strata of clay, sand, and
pebbles. If some of these pebbles consist of that peculiar flint, of which
layers more or less continuous are characteristic of the chalk, and which
include fossil shells, sponges, and foraminifera of cretaceous species, we
may confidently infer that the chalk was the oldest of the two formations.
Chronological Groups.—The number of groups into which the
fossiliferous strata may be separated are more or less numerous, according
to the views of classification which different geologists entertain; but when
we have adopted a certain system of arrangement, we immediately find that
a few only of the entire series of groups occur one upon the other in any
single section or district.
The thinning out of individual strata was before described (p. 42).But let
the diagram (Fig. 84) represent seven fossiliferous groups, instead of as
many strata. It will then be seen that in the middle all the superimposed
formations are present; but in consequence of some of them thinning out,
No. 2 and No. 5 are absent at one extremity of the section, and No. 4 at the
other.

In another diagram (Fig. 85), a real section of the geological formations
in the neighbourhood of Bristol and the Mendip Hills is presented to the
reader, as laid down on a true scale by Professor Ramsay, where the newer
groups 1, 2, 3, 4 rest unconformably on the formations 5, 6, 7 and 8. At the
southern end of the line of section we meet with the beds No. 3 (the New
Red Sandstone) resting immediately on Nos. 7 and 8, while farther north as
at Dundry Hill in Somersetshire, we behold eight groups superimposed one
upon the other, comprising all the strata from the inferior Oolite, No. 1, to
the coal and carboniferous limestone. The limited horizontal extension of
the groups 1 and 2 is owing to denudation, as these formations end abruptly,
and have left outlying patches to attest the fact of their having originally
covered a much wider area.

In order, therefore, to establish a chronological succession of fossiliferous
groups, a geologist must begin with a single section in which several sets of
strata lie one upon the other. He must then trace these formations, by
attention to their mineral character and fossils, continuously, as far as
possible, from the starting-point. As often as he meets with new groups, he
must ascertain by superposition their age relatively to those first examined,
and thus learn how to intercalate them in a tabular arrangement of the
whole.
By this means the German, French, and English geologists have
determined the succession of strata throughout a great part of Europe, and
have adopted pretty generally the following groups, almost all of which
have their representatives in the British Islands.

TABULAR VIEW OF THE FOSSILIFEROUS STRATA,
SHOWING THE ORDER OF SUPERPOSITION OR CHRONOLOGICAL SUCCESSION OF THE
PRINCIPAL GROUPS DESCRIBED IN THIS WORK.

POST-TERTIARY
EXAMPLES

POST- British
TERTIARY Clyde marine strata, with canoes (p.
146).
1.
Foreign
RECENT
Danish kitchen middens (p. 146).
Shells and mammals,
Lacustrine mud, with remains of Swiss
all of living species.
lake-dwellings (p. 148).
Marine strata inclosing Temple of
Serapis, at Puzzuoli (p. 146).
2. British
POST- Loam of Brixham cave, with flint
PLIOCENE. implements and bones of extinct and
Shells, recent living quadrupeds (p. 157)
mammalia in part Drift near Salisbury, with bones of
extinct. mammoth, Spermophilus, and stone
implements (p. 161).
Glacial drift of Scotland, with marine
shells and remains of mammoth (p. 176.
Erratics of Pagham and Selsey Bill (p.
182).
Glacial drift of Wales, with marine
fossil shells, about 1400 feet high, on
Moel Tryfaen (p. 181).
Foreign
Dordogne caves of the reindeer period
(p. 150).
Older valley-gravels of Amiens, with
flint implements and bones of extinct
mammalia (p. 152).
Loess of Rhine (p. 154).
Ancient Nile-mud forming river-
terraces (p. 154).
Loam and breccia of Liege caverns,
with human remains (pp. 156, 157).
Australian cave breccias, with bones of
extinct marsupials (p. 158).

Glacial drift of Northern Europe (p.
166, p. 174).

TERTIARY OR CAINOZOIC

British
Bridlington beds, marine Arctic fauna
(p. 189).
Glacial boulder formation of Norfolk
cliffs (p. 190).
Forest-bed of Norfolk cliffs, with
bones of Elephas meridionalis, etc. (p.
191).
3.
Chillesford and Aldeby beds, with
NEWER
marine shells, chiefly Arctic (p. 192).
PLIOCENE.
Norwich crag (p. 193).
The shells almost all
Foreign
of living species.
Eastern base of Mount Etna, with
marine shells (p. 204).
PLIOCENE
Sicilian calcareous and tufaceous strata
(p. 205, 206).
Lacustrine strata of Upper Val d’Arno
(p. 207).
Madeira leaf-bed and land-shells (p.
532).
British
4. Red crag of Suffolk, marine shells,
OLDER some of northern forms (p. 194, 195).
PLIOCENE. White or coralline crag of Suffolk (p.
Extinct species of 197).
shells forming a Foreign
large minority. Antwerp crag (p. 204).
Subapennine marls and sands (p. 208).

EXAMPLES

MIOCENE British
Wanting.
Foreign
Faluns of Touraine (p. 211).
Faluns, proper, of Bordeaux (p. 214).
Fresh-water strata of Gers (p. 215).
5. Swiss Oeningen beds, rich in plants and insects
UPPER (pp. 215-23).
MIOCENE. Marine Molasse, Switzerland (p. 223).
Majority of Bolderberg beds of Belgium (p. 224).
the Vienna basin (p. 224).
shells extinct. Beds of the Superga, near Turin (p. 226).
Deposit at Pikermé, near Athens (p. 226).
Strata of the Siwâlik hills, India (p. 226).
Marine strata of the Atlantic border in the United
States (p. 227).
Volcanic tuff and limestone of Madeira, the
Canaries, and the Azores ().
6. British
LOWER Hempstead beds, marine and fresh-water strata
MIOCENE. (p. 244).
Nearly all the Lignites and clays of Bovey Tracey (p. 245).
shells extinct. Isle of Mull leaf-bed, volcanic tuff (p. 247).
Foreign
Calcaire de la Beauce, etc. (p. 230).
Grès de Fontainebleau (p. 230).
Lacustrine strata of the Limagne d’Auvergne,
and the Cantal (p. 233).
Mayence basin (p. 242).
Radaboj beds of Croatia (p. 242).
Brown coal of Germany (p. 244).
Lower Molasse of Switzerland, fresh-water and
brackish (p. 235-9).
Rupelmonde, Kleynspawen, and Tongrian beds
of Belgium (p. 241, 242).
Nebraska beds, United States (p. 248).

Lower Miocene beds of Italy (p. 244).
Miocene flora of North Greenland (p. 239).
British
Bembridge fluvio-marine strata (p. 252).
Osborne or St. Helen’s series (p. 255).
Headon series, with marine and fresh-water
7. shells (p. 255).
UPPER Barton sands and clays (p. 258).
EOCENE. Foreign
Gypsum of Montmartre, fresh-water with
Palæotherium (p. 270).
Calcaire silicieux, or Travertin inférieur (p. 273),
Grès de Beauchamp, or Sables moyens (p. 273).
British
Bracklesham beds and Bagshot sands (p. 259).
White clays of Alum Bay and Bournemouth (p.
262).
Foreign
EOCENE 8.
Calcaire grossier, miliolitic limestone (p. 274).
MIDDLE
Soissonnais sands, or Lits coquilliers, with
EOCENE.
Nummulites planulata (p. 275).
Claiborne beds of the United States, with
Orbitoides and Zeuglodon (p. 279).
Nummulitic formation of Europe, Asia, etc. (p.
277).
British
London clay proper (p. 263).
Woolwich and Reading series, fluvio-marine (p.
9. 267).
LOWER Thanet sands (p. 269).
EOCENE. Foreign
Argile de Londres, near Dunkirk (p. 252).
Argile plastique (p. 276).
Sables de Bracheux (p. 276).

SECONDARY OR MESOZOIC.

British
Upper white chalk, with flints (p. 290).
Lower white chalk, without flints (p.
10. 298).
CRETACEOUS UPPER Chalk marl (p. 298).
CRETACEOUS. Chloritic series (or Upper Greensand),
fire-stone of Surrey (p. 298).
Gault (p. 300).
Blackdown beds (p. 301).

EXAMPLES

CRETACEOUS Foreign
Maetricht beds and Faxoe chalk (p.
233).
Pisolitic limestone of France (p. 285).
White chalk of France, Sweden, and
10. Russia (p. 286, 287).
UPPER Planer-kalk of Saxony (p. 293).
CRETACEOUS. Sands and clays of Aix-la-Chapelle (p.
302).
Hippurite limestone of South of France
(p. 305).
New Jersey, U.S., sands and marls (p.
307).
11. British
LOWER Sands of Folkestone, Sandgate, and
CRETACEOUS Hythe (p. 308).
or Atherfield clay, with Perna mulleti (p.
NEOCOMIAN. 309).
Punfield marine beds, with Vicarya
lujana (p. 318).
Speeton clay of Flamborough Head and
Tealby (p. 311).
Weald clay of Surrey, Kent, and Sussex,
fresh-water, with Cypris (p. 313-5).
Hastings sands (p. 316-8).

Foreign
Neocomian of Neufchatel, and Hils
conglomerate of North Germany (p.
312).
Wealden beds of Hanover (p. 319).
British
Upper Purbeck beds, fresh-water (p.
323).
Middle Purbeck, with numerous
marsupial quadrupeds, etc. (p. 324).
Lower Purbeck, fresh-water, with
12.
intercalated dirt-bed (p. 330).
UPPER
Portland stone and sand. (p. 334).
OOLITE.
Kimmeridge clay (p. 335).
Foreign
Marnes à gryphées virgules of Argonne
(p. 336).
Lithographic-stone of Solenhofen, with
Archæopteryx (p. 337).
British
OOLITE Coral rag of Berkshire, Wilts, and
Yorkshire (p. 339).
13. Oxford clay, with belemnites and
MIDDLE Ammonite (p. 340).
OOLITE. Kelloway rock of Wilts and Yorkshire
(p. 341).
Foreign
Nerinæan limestone of the Jura (p. 339).
British
Cornbrash and forest marble (p. 341).
Great or Bath oolite of Bradford (p.
14.
342).
LOWER
Stonesfield slate, with marsupials and
OOLITE.
Araucaria (p. 345).
Fuller’s earth of Bath (p. 348).
Inferior oolite (p. 349).

Upper Lias, argillaceous, with
Ammonites striatulus (p. 353).
Shale and limestone, with Ammonites
bifrons (p. 353).
15. Middle Lias or Marlstone series, with
LIAS
LIAS. zones containing characteristic
Ammonites (p. 353).
Lower Lias, also with zones
characterised by peculiar Ammonites (p.
356).
TRIAS British
Rhætic, Penarth or Avicula contorta
beds (beds of passage) (p. 366).
Keuper or Upper New Red sandstone,
etc. (p. 369).
Red shales of Cheshire and Lancashire,
with rock-salt (p. 371).
Dolomite conglomerate of Bristol (p.
16.
373).
UPPER TRIAS.
Foreign
Keuper beds of Germany (p. 375).
St. Cassian or Hallstadt beds, with rich
marine fauna (p. 376).
Coal-field of Richmond, Virginia (p.
382).
Chatham coal-field, North Carolina (p.
383).
British
17.
Wanting.
MIDDLE
Foreign
TRIAS.
Muschelkalk of Germany (p. 378).
18. British
LOWER TRIAS. Bunter or Lower New Red sandstone of
Lancashire and Cheshire (p. 372).
Foreign
Bunter-sandstein of Germany (p. 380).
Red sandstone of Connecticut Valley,

with footprints of birds and reptiles (p.
381).

PRIMARY OR PALÆOZOIC
EXAMPLES

British
Upper Permian of St. Bees’
Head, Cumberland (p. 386).
Middle Permian, magnesian
limestone, and marl-slate of
Durham and Yorkshire, with
Protosaurus (p. 387).
Lower Permian sandstones
and breccias of Penrith and
Dumfriesshire, intercalated (p.
19. 390).
PERMIAN
PERMIAN. Foreign
Dark-coloured shales of
Thuringia (p. 392).
Zechstein or Dolomitic
limestone (p. 392).
Mergel-schiefer or Kupfer-
schiefer (p. 392).
Rothliegendes of Thuringia,
with Psaronius (p. 392).
Magnesian limestones, etc., of
Russia (p. 393).
CARBONIFEROUS 20. British
UPPER Coal-measures of South
CARBONIFEROUS. Wales, with underclays
inclosing Stigmaria (p. 397).
Coal-measures of north and
central England (p. 395).
Millstone grit (p. 395).
Yoredale series of Yorkshire
(p. 395).

Coal-field of Kilkenny with
Labyrinthodont (p. 407).
Foreign
Coal-field of Saarbruck, with
Archegosaurus (p. 406).
Carboniferous strata of South
Joggins, Nova Scotia (p. 409).
Pennsylvania coal-field (p.
403).
British
Mountain limestone of Wales
and South of England (p.
430).
Same in Ireland (p. 437437).
Carboniferous limestone of
21.
Scotland alternating with
LOWER
coal-bearing sandstones (p.
CARBONIFEROUS.
396).
Erect trees in volcanic ash in
the Island of Arran (p. 546).
Foreign
Mountain limestone of
Belgium (p. 436).
DEVONIAN or 22. British
OLD RED UPPER Yellow sandstone of Dura
SANDSTONE DEVONIAN. Den, with Holoptychius, etc.
(p. 440); and of Ireland with
Anodon Jukesii (p. 441).
Sandstones of Forfarshire and
Perthshire, with Holoptychius,
etc. (p. 442).
Pilton group of North Devon
(p. 449).
Petherwyn group of Cornwall,
with Clymenia and Cypridina
(p. 451).
Foreign

Clymenien-kalk and
Cypridinen-schiefer of
Germany (p. 450)
British
Bituminous schists of Gamrie,
Caithness, etc., with numerous
fish (p. 443).
Ilfracombe beds with peculiar
trilobites and corals (p. 450).
23. Limestones of Torquay, with
MIDDLE broad-winged Spirifers (p.
DEVONIAN. 451).
Foreign
Eifel limestone, with
underlying schists containing
Calceola (p. 453).
Devonian strata of Russia (p.
454).
British
Arbroath paving-stones, with
Cephalaspis and Pterygotus
(p. 446).
Lower sandstones of
Forfarshire, with Pterygotus
24. (p. 446).
LOWER Sandstones and slates of the
DEVONIAN. Foreland and Linton (p. 454).
Foreign
Oriskany sandstone of
Western Canada and New
York (p. 456).
Sandstones of Gaspe, with
Cephalaspis (p. 455 ).

EXAMPLES

British
Upper Ludlow formation, Downton
sandstone, with bone-bed (p. 459).
Lower Ludlow formation, with oldest
known fish remains (p. 461).
Wenlock limestone and shale (p. 465).
Woolhope limestone and grit (p. 467).
Tarannon shales (p. 468).
Beds of passage between Upper and
25. Lower Silurian:
UPPER Upper Llandovery, or May-hill
SILURIAN sandstone, with Pentamerus oblongus,
etc. (p. 468).
Lower Llandovery slates (p. 469).
Foreign
Niagara limestone, with Calymene,
SILURIAN Homalonotus, etc. (p. 479).
Clinton group of America, with
Pentamerus oblongus, etc. (p. 479).
Silurian strata of Russia, with
Pentamerus (p. 477).
British
Bala and Caradoc beds (p. 470).
Llandeilo flags (p. 473).
Arenig or Stiper-stones group (Lower
Llandeilo of Murchison) (p. 475).
26.
Foreign
LOWER
Ungulite or Obolus grit of Russia (p.
SILURIAN.
477).
Trenton limestone, and other Lower
Silurian groups of North America (p.
479).
Lower Silurian of Sweden (p. 477).
CAMBRIAN 27. British
UPPER Tremadoc slates (p. 483).
CAMBRIAN. Lingula flags, with Lingula Davisii (p.
484).

Foreign
“Primordial” zone of Bohemia in part,
with trilobites of the genera
Paradoxides, etc. (p. 487).
Alum schists of Sweden and Norway
(p. 489).
Potsdam sandstone, with
Dikelocephalus and Obolella (p. 489).
British
Menevian beds of Wales, with
Paradoxides Davidis, etc. (p. 484).
Longmynd group, comprising the
28. Harlech grits and Llanberis slates (p.
LOWER 485).
CAMBRIAN. Foreign
Lower portion of Barrande’s
“Primordial” zone in Bohemia (p. 486).
Fucoid sandstones of Sweden (p. 489).
Huronian series of Canada? (p. 490).
British
Fundamental gneiss of the Hebrides?
(p. 493).
29. Hypersthene rocks of Skye? (p. 491).
UPPER Foreign
LAURENTIAN. Labradorite series north of the river St.
Lawrence in Canada (p. 491).
Adirondack mountains of New York (p.
LAURENTIAN 491).
British
Wanting?
Foreign
30.
Beds of gneiss and quartzite, with
LOWER
interstratified limestones, in one of
LAURENTIAN.
which, 1000 feet thick, occurs a
foraminifer, Eozoon Canadense, the
oldest known fossil (p. 491).

CHAPTER IX.
CLASSIFICATION OF TERTIARY FORMATIONS.

Order of Succession of Sedimentary Formations. —
Frequent Unconformability of Strata. — Imperfection of the
Record. — Defectiveness of the Monuments greater in
Proportion to their Antiquity. — Reasons for studying the
newer Groups first. — Nomenclature of Formations. —
Detached Tertiary Formations scattered over Europe. —
Value of the Shell-bearing Mollusca in Classification. —
Classification of Tertiary Strata. — Eocene, Miocene, and
Pliocene Terms explained.

By reference to the tables given at the end of the last chapter the reader
will see that when the fossiliferous rocks are arranged chronologically, we
have first to consider the Post-tertiary and then the Tertiary or Cainozoic
formations, and afterwards to pass on to those of older date.

Order of Superposition.—The diagram (Fig. 86) will show the order of
superposition of these deposits, assuming them all to be visible in one
continuous section. In nature, as before hinted (p. 107), we have never an
opportunity of seeing the whole of them so displayed in a single region;
first, because sedimentary deposition is confined, during any one geological
period, to limited areas; and secondly, because strata, after they have been
formed, are liable to be utterly annihilated over wide areas by denudation.

But wherever certain members of the series are present, they overlie one
another in the order indicated in the diagram, though not always in the exact
manner there represented, because some of them repose occasionally in
unconformable stratification on others. This mode of superposition has been
already explained (p. 94, p. 111), where I pointed out that the discordance
which implies a considerable lapse of time between two formations in
juxtaposition is almost invariably accompanied by a great dissimilarity in
the species of organic remains.
Frequent Unconformability of Strata.—Where the widest gaps appear
in the sequence of the fossil forms, as between the Permian and Triassic
rocks, or between the Cretaceous and Eocene, examples of such
unconformability are very frequent. But they are also met with in some part
or other of the world at the junction of almost all the other principal
formations, and sometimes the subordinate divisions of any one of the
leading groups may be found lying unconformably on another subordinate
member of the same—the Upper, for example, on the Lower Silurian, or the
superior division of the Old Red Sandstone on a lower member of the same,
and so forth. Instances of such irregularities in the mode of succession of
the strata are the more intelligible the more we extend our survey of the
fossiliferous formations, for we are continually bringing to light deposits of
intermediate date, which have to be intercalated between those previously
known, and which reveal to us a long series of events, of which
antecedently to such discoveries we had no knowledge.
But while unconformability invariably bears testimony to a lapse of
unrepresented time, the conformability of two sets of strata in contact by no
means implies that the newer formation immediately succeeded the older
one. It simply implies that the ancient rocks were subjected to no
movements of such a nature as to tilt, bend, or break them before the more
modern formation was superimposed. It does not show that the earth’s crust
was motionless in the region in question, for there may have been a gradual
sinking or rising, extending uniformly over a large surface, and yet, during
such movement, the stratified rocks may have retained their original
horizontality of position. There may have been a conversion of a wide area
from sea into land and from land into sea, and during these changes of level
some strata may have been slowly removed by aqueous action, and after
this new strata may be superimposed, differing perhaps in date by thousands
of years or centuries, and yet resting conformably on the older set. There

may even be a blending of the materials constituting the older deposit with
those of the newer, so as to give rise to a passage in the mineral character of
the one rock into the other as if there had been no break or interruption in
the depositing process.
Imperfection of the Record.—Although by the frequent discovery of
new sets of intermediate strata the transition from one type of organic
remains to another is becoming less and less abrupt, yet the entire series of
records appears to the geologists now living far more fragmentary and
defective than it seemed to their predecessors half a century ago. The earlier
inquirers, as often as they encountered a break in the regular sequence of
formations, connected it theoretically with a sudden and violent catastrophe,
which had put an end to the regular course of events that had been going on
uninterruptedly for ages, annihilating at the same time all or nearly all the
organic beings which had previously flourished, after which, order being re-
established, a new series of events was initiated. In proportion as our faith
in these views grows weaker, and the phenomena of the organic or
inorganic world presented to us by geology seem explicable on the
hypothesis of gradual and insensible changes, varied only by occasional
convulsions, on a scale comparable to that witnessed in historical times; and
in proportion as it is thought possible that former fluctuations in the organic
world may be due to the indefinite modifiability of species without the
necessity of assuming new and independent acts of creation, the number
and magnitude of the gaps which still remain, or the extreme imperfection
of the record, become more and more striking, and what we possess of the
ancient annals of the earth’s history appears as nothing when contrasted
with that which has been lost.
When we examine a large area such as Europe, the average as well as the
extreme height above the sea attained by the older formations is usually
found to exceed that reached by the more modern ones, the primary or
palaeozoic rising higher than the secondary, and these in their turn than the
tertiary; while in reference to the three divisions of the tertiary, the lowest or
Eocene group attains a higher summit-level than the Miocene, and these
again a greater height than the Pliocene formations. Lastly, the post-tertiary
deposits, such, at least, as are of marine origin, are most commonly
restricted to much more moderate elevations above the sea-level than the
tertiary strata.

It is also observed that strata, in proportion as they are of newer date,
bear the nearest resemblance in mineral character to those which are now in
the progress of formation in seas or lakes, the newest of all consisting
principally of soft mud or loose sand, in some places full of shells, corals,
or other organic bodies, animal or vegetable, in others wholly devoid of
such remains. The farther we recede from the present time, and the higher
the antiquity of the formations which we examine, the greater are the
changes which the sedimentary deposits have undergone. Time, as I have
explained in Chapters V, VI, and VII, has multiplied the effects of
condensation by pressure and cementation, and the modification produced
by heat, fracture, contortion, upheaval, and denudation. The organic
remains also have sometimes been obliterated entirely, or the mineral matter
of which they were composed has been removed and replaced by other
substances.
Why newer Groups should be studied first.—We likewise observe that
the older the rocks the more widely do their organic remains depart from
the types of the living creation. First, we find in the newer tertiary rocks a
few species which no longer exist, mixed with many living ones, and then,
as we go farther back, many genera and families at present unknown make
their appearance, until we come to strata in which the fossil relics of
existing species are nowhere to be detected, except a few of the lowest
forms of invertebrate, while some orders of animals and plants wholly
unrepresented in the living world begin to be conspicuous.
When we study, therefore, the geological records of the earth and its
inhabitants, we find, as in human history, the defectiveness and obscurity of
the monuments always increasing the remoter the era to which we refer, and
the difficulty of determining the true chronological relations of rocks is
more and more enhanced, especially when we are comparing those which
were formed simultaneously in very distant regions of the globe. Hence we
advance with securer steps when we begin with the study of the geological
records of later times, proceeding from the newer to the older, or from the
more to the less known.
In thus inverting what might at first seem to be the more natural order of
historical research, we must bear in mind that each of the periods above
enumerated, even the shortest, such as the Post-tertiary, or the Pliocene,
Miocene, or Eocene, embrace a succession of events of vast extent, so that

to give a satisfactory account of what we already know of any one of them
would require many volumes. When, therefore, we approach one of the
newer groups before endeavouring to decipher the monuments of an older
one, it is like endeavouring to master the history of our own country and
that of some contemporary nations, before we enter upon Roman History, or
like investigating the annals of Ancient Italy and Greece before we
approach those of Egypt and Assyria.
Nomenclature.—The origin of the terms Primary and Secondary, and the
synonymous terms Palaeozoic, and Mesozoic, were explained in Chapter
VIII, p. 123.
The Tertiary or Cainozoic strata (see p. 123) were so called because they
were all posterior in date to the Secondary series, of which last the Chalk of
Cretaceous, No. 9, Fig. 86, constitutes the newest group. The whole of them
were at first confounded with the superficial alluviums of Europe; and it
was long before their real extent and thickness, and the various ages to
which they belong, were fully recognised. They were observed to occur in
patches, some of fresh-water, others of marine origin, their geographical
area being usually small as compared to the secondary formations, and their
position often suggesting the idea of their having been deposited in different
bays, lakes, estuaries, or inland seas, after a large portion of the space now
occupied by Europe had already been converted into dry land.
The first deposits of this class, of which the characters were accurately
determined, were those occurring in the neighbourhood of Paris, described
in 1810 by MM. Cuvier and Brongniart. They were ascertained to consist of
successive sets of strata, some of marine, others of fresh-water origin, lying
one upon the other. The fossil shells and corals were perceived to be almost
all of unknown species, and to have in general a near affinity to those now
inhabiting warmer seas. The bones and skeletons of land animals, some of
them of large size, and belonging to more than forty distinct species, were
examined by Cuvier, and declared by him not to agree specifically, nor most
of them even generically, with any hitherto observed in the living creation.
Strata were soon afterwards brought to light in the vicinity of London,
and in Hampshire, which, although dissimilar in mineral composition, were
justly inferred by Mr. T. Webster to be of the same age as those of Paris,
because the greater number of the fossil shells were specifically identical.
For the same reason, rocks found on the Gironde, in the South of France,

and at certain points in the North of Italy, were suspected to be of
contemporaneous origin.
Another important discovery was soon afterwards made by Brocchi in
Italy, who investigated the argillaceous and sandy deposits, replete with
shells, which form a low range of hills, flanking the Apennines on both
sides, from the plains of the Po to Calabria. These lower hills were called by
him the Subapennines, and were formed of strata chiefly marine, and newer
than those of Paris and London.
Another tertiary group occurring in the neighbourhood of Bordeaux and
Dax, in the South of France, was examined by M. de Basterot in 1825, who
described and figured several hundred species of shells, which differed for
the most part both from the Parisian series and those of the Subapennine
hills. It was soon, therefore, suspected that this fauna might belong to a
period intermediate between that of the Parisian and Subapennine strata,
and it was not long before the evidence of superposition was brought to
bear in support of this opinion; for other strata, contemporaneous with those
of Bordeaux, were observed in one district (the Valley of the Loire), to
overlie the Parisian formation, and in another (in Piedmont) to underlie the
Subapennine beds. The first example of these was pointed out in 1829 by
M. Desnoyers, who ascertained that the sand and marl of marine origin
called faluns, near Tours, in the basin of the Loire, full of sea-shells and
corals, rested upon a lacustrine formation, which constitutes the uppermost
subdivision of the Parisian group, extending continuously throughout a
great table-land intervening between the basin of the Seine and that of the
Loire. The other example occurs in Italy, where strata containing many
fossils similar to those of Bordeaux were observed by Bonelli and others in
the environs of Turin, subjacent to strata belonging to the Subapennine
group of Brocchi.
Value of Testacean Fossils in Classification.—It will be observed that
in the foregoing allusions to organic remains, the testacea or the shell-
bearing mollusca are selected as the most useful and convenient class for
the purposes of general classification. In the first place, they are more
universally distributed through strata of every age than any other organic
bodies. Those families of fossils which are of rare and casual occurrence are
absolutely of no avail in establishing a chronological arrangement. If we
have plants alone in one group of strata and the bones of mammalia in

another, we can draw no conclusion respecting the affinity or discordance
of the organic beings of the two epochs compared; and the same may be
said if we have plants and vertebrated animals in one series and only shells
in another. Although corals are more abundant, in a fossil state, than plants,
reptiles, or fish, they are still rare when contrasted with shells, because they
are more dependent for their well-being on the constant clearness of the
water, and are, therefore, less likely to be included in rocks which endure in
consequence of their thickness and the copiousness of sediment which
prevailed when they originated. The utility of the testacea is, moreover,
enhanced by the circumstance that some forms are proper to the sea, others
to the land, and others to fresh water. Rivers scarcely ever fail to carry
down into their deltas some land-shells, together with species which are at
once fluviatile and lacustrine. By this means we learn what terrestrial, fresh-
water, and marine species coexisted at particular eras of the past: and
having thus identified strata formed in seas with others which originated
contemporaneously in inland lakes, we are then enabled to advance a step
farther, and show that certain quadrupeds or aquatic plants, found fossil in
lacustrine formations, inhabited the globe at the same period when certain
fish, reptiles, and zoophytes lived in the ocean.
Among other characters of the molluscous animals, which render them
extremely valuable in settling chronological questions in geology, may be
mentioned, first, the wide geographical range of many species; and,
secondly, what is probably a consequence of the former, the great duration
of species in this class, for they appear to have surpassed in longevity the
greater number of the mammalia and fish. Had each species inhabited a
very limited space, it could never, when imbedded in strata, have enabled
the geologist to identify deposits at distant points; or had they each lasted
but for a brief period, they could have thrown no light on the connection of
rocks placed far from each other in the chronological, or, as it is often
termed, vertical series.
Classification of Tertiary Strata.—Many authors have divided the
European Tertiary strata into three groups—lower, middle, and upper; the
lower comprising the oldest formations of Paris and London before
mentioned; the middle those of Bordeaux and Touraine; and the upper all
those newer than the middle group.

In the first edition of the Principles of Geology, I divided the whole of the
Tertiary formations into four groups, characterised by the percentage of
recent shells which they contained. The lower tertiary strata of London and
Paris were thought by M. Deshayes to contain only 3½ per cent of recent
species, and were termed Eocene. The middle tertiary of the Loire and
Gironde had, according to the specific determinations of the same
conchologist, 17 per cent, and formed the Miocene division. The
Subapennine beds contained 35 to 50 per cent, and were termed Older
Pliocene, while still more recent beds in Sicily, which had from 90 to 95 per
cent of species identical with those now living, were called Newer Pliocene.
The first of the above terms, Eocene, is derived from eos, dawn, and cainos,
recent, because the fossil shells of this period contain an extremely small
proportion of living species, which may be looked upon as indicating the
dawn of the existing state of the testaceous fauna, no recent species having
been detected in the older or secondary rocks.
The term Miocene (from meion, less, and cainos, recent) is intended to
express a minor proportion of recent species (of testacea), the term Pliocene
(from pleion, more, and cainos, recent) a comparative plurality of the same.
It may assist the memory of students to remind them, that the Miocene
contain a minor proportion, and Pliocene a comparative plurality of recent
species; and that the greater number of recent species always implies the
more modern origin of the strata.
It has sometimes been objected to this nomenclature that certain species
of infusoria found in the chalk are still existing, and, on the other hand, the
Miocene and Older Pliocene deposits often contain the remains of
mammalia, reptiles, and fish, exclusively of extinct species. But the reader
must bear in mind that the terms Eocene, Miocene, and Pliocene were
originally invented with reference purely to conchological data, and in that
sense have always been and are still used by me.
Since the year 1830 the number of known shells, both recent and fossil,
has largely increased, and their identification has been more accurately
determined. Hence some modifications have been required in the
classifications founded on less perfect materials. The Eocene, Miocene, and
Pliocene periods have been made to comprehend certain sets of strata of
which the fossils do not always conform strictly in the proportion of recent

to extinct species with the definitions first given by me, or which are
implied in the etymology of those terms.

CHAPTER X.
RECENT AND POST-PLIOCENE PERIODS.

Recent and Post-pliocene Periods. — Terms defined. —
Formations of the Recent Period. — Modern littoral
Deposits containing Works of Art near Naples. — Danish
Peat and Shell-mounds. — Swiss Lake-dwellings. —
Periods of Stone, Bronze, and Iron. — Post-pliocene
Formations. — Coexistence of Man with extinct Mammalia.
— Reindeer Period of South of France. — Alluvial Deposits
of Paleolithic Age. — Higher and Lower-level Valley-
gravels. — Loess or Inundation-mud of the Nile, Rhine, etc.
— Origin of Caverns. — Remains of Man and extinct
Quadrupeds in Cavern Deposits. — Cave of Kirkdale. —
Australian Cave-breccias. — Geographical Relationship of
the Provinces of living Vertebrata and those of extinct Post-
pliocene Species. — Extinct struthious Birds of New
Zealand. — Climate of the Post-pliocene Period. —
Comparative Longevity of Species in the Mammalia and
Testacea. — Teeth of Recent and Post-pliocene Mammalia.

We have seen in the last chapter that the uppermost or newest strata are
called Post-tertiary, as being more modern than the Tertiary. It will also be
observed that the Post-tertiary formations are divided into two subordinate
groups: the Recent, and Post-pliocene. In the former, or the Recent, the
mammalia as well as the shells are identical with species now living:
whereas in the Post-pliocene, the shells being all of living forms, a part, and
often a considerable part, of the mammalia belonged to extinct species. To
this nomenclature it may be objected that the term Post-pliocene should in
strictness include all geological monuments posterior in date to the
Pliocene; but when I have occasion to speak of the whole collectively, I

shall call them Post-tertiary, and reserve the term Post-pliocene for the older
Post-tertiary formations, while the Upper or newer ones will be called
“Recent.”
Cases will occur where it may be scarcely possible to draw the boundary
line between the Recent and Post-pliocene deposits; and we must expect
these difficulties to increase rather than diminish with every advance in our
knowledge, and in proportion as gaps are filled up in the series of records.

RECENT PERIOD

It was stated in the sixth chapter, when I treated of denudation, that the
dry land, or that part of the earth’s surface which is not covered by the
waters of lakes or seas, is generally wasting away by the incessant action of
rain and rivers, and in some cases by the undermining and removing power
of waves and tides on the sea-coast. But the rate of waste is very unequal,
since the level and gently sloping lands, where they are protected by a
continuous covering of vegetation, escape nearly all wear and tear, so that
they may remain for ages in a stationary condition, while the removal of
matter is constantly widening and deepening the intervening ravines and
valleys.
The materials, both fine and coarse, carried down annually by rivers from
the higher regions to the lower, and deposited in successive strata in the
basins of seas and lakes, must be of enormous volume. We are always liable
to underrate their magnitude, because the accumulation of strata is going on
out of sight.
There are, however, causes at work which, in the course of centuries,
tend to render visible these modern formations, whether of marine or
lacustrine origin. For a large portion of the earth’s crust is always
undergoing a change of level, some areas rising and others sinking at the
rate of a few inches, or a few feet, perhaps sometimes yards, in a century;
so that spaces which were once subaqueous are gradually converted into
land, and others which were high and dry become submerged. In
consequence of such movements we find in certain regions, as in Cashmere,
for example, where the mountains are often shaken by earthquakes, deposits
which were formed in lakes in the historical period, but through which
rivers have now cut deep and wide channels. In lacustrine strata thus
intersected, works of art and fresh-water shells are seen. In other districts on

the borders of the sea, usually at very moderate elevations above its level,
raised beaches occur, or marine littoral deposits, such as those in which, on
the borders of the Bay of Baiæ, near Naples, the well-known temple of
Serapis was imbedded. In that case the date of the monument buried in the
marine strata is ascertainable, but in many other instances the exact age of
the remains of human workmanship is uncertain, as in the estuary of the
Clyde at Glasgow, where many canoes have been exhumed, with other
works of art, all assignable to some part of the Recent Period.
Danish Peat and Shell-mounds or Kitchen-middens.—Sometimes we
obtain evidence, without the aid of a change of level, of events which took
place in pre-historic times. The combined labours, for example, of the
antiquary, zoologist, and botanist have brought to light many monuments of
the early inhabitants buried in peat-mosses in Denmark. Their geological
age is determined by the fact that, not only the contemporaneous fresh-
water and land shells, but all the quadrupeds, found in the peat, agree
specifically with those now inhabiting the same districts, or which are
known to have been indigenous in Denmark within the memory of man. In
the lower beds of peat (a deposit varying from 20 to 30 feet in thickness),
weapons of stone accompany trunks of the Scotch fir, Pinus sylvestris. This
peat may be referred to that part of the stone period for which Sir John
Lubbock proposed the name of “Neolithic”[1] in contradistinction to a still
older era, termed by him “Paleolithic,” and which will be described in the
sequel. In the higher portions of the same Danish bogs, bronze implements
are associated with trunks and acorns of the common oak. It appears that
the pine has never been a native of Denmark in historical times, and it
seems to have given place to the oak about the time when articles and
instruments of bronze superseded those of stone. It also appears that, at a
still later period, the oak itself became scarce, and was nearly supplanted by
the beech, a tree which now flourishes luxuriantly in Denmark. Again, at
the still later epoch when the beech-tree abounded, tools of iron were
introduced, and were gradually substituted for those of bronze.
On the coasts of the Danish islands in the Baltic, certain mounds, called
in those countries “Kjökken-mödding,” or “kitchen-middens,” occur,
consisting chiefly of the castaway shells of the oyster, cockle, periwinkle,
and other eatable kinds of molluscs. The mounds are from three to ten feet
high, and from 100 to 1000 feet in their longest diameter. They greatly
resemble heaps of shells formed by the Red Indians of North America along

the eastern shores of the United States. In the old refuse-heaps, recently
studied by the Danish antiquaries and naturalists with great skill and
diligence, no implements of metal have ever been detected. All the knives,
hatchets, and other tools, are of stone, horn, bone, or wood. With them are
often intermixed fragments of rude pottery, charcoal and cinders, and the
bones of quadrupeds on which the rude people fed. These bones belong to
wild species still living in Europe, though some of them, like the beaver,
have long been extirpated in Denmark. The only animal which they seem to
have domesticated was the dog.
As there is an entire absence of metallic tools, these refuse-heaps are
referred to the Neolithic division of the age of stone, which immediately
preceded in Denmark the age of bronze. It appears that a race more
advanced in civilisation, armed with weapons of that mixed metal, invaded
Scandinavia, and ousted the aborigines.
Lacustrine Habitations of Switzerland.—In Switzerland a different
class of monuments, illustrating the successive ages of stone, bronze, and
iron, has been of late years investigated with great success, and especially
since 1854, in which year Dr. F. Keller explored near the shore at Meilen, in
the bottom of the lake of Zurich, the ruins of an old village, originally built
on numerous wooden piles, driven, at some unknown period, into the
muddy bed of the lake. Since then a great many other localities, more than a
hundred and fifty in all, have been detected of similar pile-dwellings,
situated near the borders of the Swiss lakes, at points where the depth of
water does not exceed 15 feet.[2] The superficial mud in such cases is filled
with various articles, many hundreds of them being often dredged up from a
very limited area. Thousands of piles, decayed at their upper extremities,
are often met with still firmly fixed in the mud.
As the ages of stone, bronze, and iron merely indicate successive stages
of civilisation, they may all have coexisted at once in different parts of the
globe, and even in contiguous regions, among nations having little
intercourse with each other. To make out, therefore, a distinct chronological
series of monuments is only possible when our observations are confined to
a limited district, such as Switzerland.
The relative antiquity of the pile-dwellings, which belong respectively to
the ages of stone and bronze, is clearly illustrated by the associations of the
tools with certain groups of animal remains. Where the tools are of stone,

the castaway bones which served for the food of the ancient people are
those of deer, the wild boar, and wild ox, which abounded when society was
in the hunter state. But the bones of the later or bronze epoch were chiefly
those of the domestic ox, goat, and pig, indicating progress in civilisation.
Some villages of the stone age are of later date than others, and exhibit
signs of an improved state of the arts. Among their relics are discovered
carbonised grains of wheat and barley, and pieces of bread, proving that the
cultivation of cereals had begun. In the same settlements, also, cloth, made
of woven flax and straw, has been detected.
The pottery of the bronze age in Switzerland is of a finer texture, and
more elegant in form, than that of the age of stone. At Nidau, on the lake of
Bienne, articles of iron have also been discovered, so that this settlement
was evidently not abandoned till that metal had come into use.
At La Thène, in the northern angle of the lake of Neufchâtel, a great
many articles of iron have been obtained, which in form and ornamentation
are entirely different both from those of the bronze period and from those
used by the Romans. Gaulish and Celtic coins have also been found there
by MM. Schwab and Desor. They agree in character with remains,
including many iron swords, which have been found at Tiefenau, near
Berne, in ground supposed to have been a battle-field; and their date
appears to have been anterior to the great Roman invasion of Northern
Europe, though perhaps not long before that event.[3] Coins, which
sometimes occur in deposits of the age of iron, have never yet been found in
formations of the ages of bronze or stone.
The period of bronze must have been one of foreign commerce, as tin,
which enters into this metallic mixture in the proportion of about ten per
cent to the copper, was obtained by the ancients chiefly from Cornwall.[4]
Very few human bones of the bronze period have been met with in the
Danish peat, or in the Swiss lake-dwellings, and this scarcity is generally
attributed by archæologists to the custom of burning the dead, which
prevailed in the age of bronze.

POST-PLIOCENE PERIOD

From the foregoing observations we may infer that the ages of iron and
bronze in Northern and Central Europe were preceded by a stone age, the
Neolithic, referable to that division of the post-tertiary epoch which I have

called Recent, when the mammalia as well as the other organic remains
accompanying the stone implements were of living species. But memorials
have of late been brought to light of a still older age of stone, for which, as
above stated, the name Paleolithic has been proposed, when man was
contemporary in Europe with the elephant and rhinoceros, and various other
animals, of which many of the most conspicuous have long since died out.
Reindeer Period in South of France.—In the larger number of the
caves of Europe, as for example in those of England, Belgium, Germany,
and many parts of France, the animal remains agree specifically with the
fauna of this oldest division of the age of stone, or that to which belongs the
drift of Amiens and Abbeville presently to be mentioned, containing flint
implements of a very antique type. But there are some caves in the
departments of Dordogne, Aude, and other parts of the south of France,
which are believed by M. Lartet to be of intermediate date between the
Paleolithic and Neolithic periods. To this intermediate era M. Lartet gave, in
1863, the name of the “reindeer period,” because vast quantities of the
bones and horns of that deer have been met with in the French caverns. In
some cases separate plates of molars of the mammoth, and several teeth of
the great Irish deer, Cervus megaceros, and of the cave-lion, Felis spelæa,
have been found mixed up with cut and carved bones of reindeer. On one of
these sculptured bones in the cave of Perigord, a rude representation of the
mammoth, with its long curved tusks and covering of wool, occurs, which
is regarded by M. Lartet as placing beyond all doubt the fact that the early
inhabitants of these caves must have seen this species of elephant still living
in France. The presence of the marmot, as well as the reindeer and some
other northern animals, in these caverns seems to imply a colder climate
than that of the Swiss lake-dwellings, in which no remains of reindeer have
as yet been discovered. The absence of this last in the old lacustrine
habitations of Switzerland is the more significant, because in a cave in the
neighbourhood of the lake of Geneva, namely, that of Mont Saleve, bones
of the reindeer occur with flint implements similar to those of the caverns of
Dordogne and Perigord.
The state of the arts, as exemplified by the instruments found in these
caverns of the reindeer period, is somewhat more advanced than that which
characterises the tools of the Amiens drift, but is nevertheless more rude
than that of the Swiss lake-dwellings. No metallic articles occur, and the
stone hatchets are not ground after the fashion of celts; the needles of bone

are shaped in a workmanlike style, having their eyes drilled with
consummate skill.
The formations above alluded to, which are as yet but imperfectly
known, may be classed as belonging to the close of the Paleolithic era, of
the monuments of which I am now about to treat.
Alluvial Deposits of the Paleolithic Age.—The alluvial and marine
deposits of the Paleolithic age, the earliest to which any vestiges of man
have yet been traced back, belong to a time when the physical geography of
Europe differed in a marked degree from that now prevailing. In the
Neolithic period, the valleys and rivers coincided almost entirely with those
by which the present drainage of the land is effected, and the peat-mosses
were the same as those now growing. The situation of the shell-mounds and
lake-dwellings above alluded to is such as to imply that the topography of
the districts where they are observed has not subsequently undergone any
material alteration. Whereas we no sooner examine the Post-pliocene
formations, in which the remains of so many extinct mammalia are found,
than we at once perceive a more decided discrepancy between the former
and present outline of the surface. Since those deposits originated, changes
of considerable magnitude have been effected in the depth and width of
many valleys, as also in the direction of the superficial and subterranean
drainage, and, as is manifest near the sea-coast, in the relative position of
land and water. In Fig. 87 an ideal section is given, illustrating the different
position which the Recent and Post-pliocene alluvial deposits occupy in
many European valleys.

The peat, No. 1, has been formed in a low part of the modern alluvial
plain, in parts of which gravel No. 2 of the recent period is seen. Over this

gravel the loam or fine sediment 2′ has in many places been deposited by
the river during floods which covered nearly the whole alluvial plain.
No. 3 represents an older alluvium, composed of sand and gravel, formed
before the valley had been excavated to its present depth. It contains the
remains of fluviatile shells of living species associated with the bones of
mammalia, in part of recent, and in part of extinct species. Among the latter,
the mammoth (E. primigenius) and the Siberian rhinoceros (R. tichorhinus)
are the most common in Europe. No. 3′ is a remnant of the loam or brick-
earth by which No. 3 was overspread. No. 4 is a still older and more
elevated terrace, similar in its composition and organic remains to No. 3,
and covered in like manner with its inundation-mud, 4′. Sometimes the
valley-gravels of older date are entirely missing, or there is only one, and
occasionally there are more than two, marking as many successive stages in
the excavation of the valley. They usually occur at heights varying from 10
to 100 feet, sometimes on the right and sometimes on the left side of the
existing river-plain, but rarely in great strength on exactly opposite sides of
the valley.
Among the genera of extinct quadrupeds most frequently met with in
England, France, Germany, and other parts of Europe, are the elephant,
rhinoceros, hippopotamus, horse, great Irish deer, bear, tiger, and hyæna. In
the peat, No. 1 (Fig. 87), and in the more modern gravel and silt (No. 2),
works of art of the ages of iron and bronze, and of the later or Neolithic
stone period, already described, are met with. In the more ancient or
Paleolithic gravels, 3 and 4, there have been found of late years in several
valleys in France and England—as, for example, in those of the Seine and
Somme, and of the Thames and Ouse, near Bedford—stone implements of a
rude type, showing that man coexisted in those districts with the mammoth
and other extinct quadrupeds of the genera above enumerated. In 1847, M.
Boucher de Perthes observed in an ancient alluvium at Abbeville, in
Picardy, the bones of extinct mammalia associated in such a manner with
flint implements of a rude type as to lead him to infer that both the organic
remains and the works of art were referable to one and the same period.
This inference was soon after confirmed by Mr. Prestwich, who found in
1859 a flint tool in situ in the same stratum at Amiens that contained the
remains of extinct mammalia.

The flint implements found at Abbeville and Amiens are most of them
considered to be hatchets and spear-heads, and are different from those
commonly called “celts.” These celts, so often found in the recent
formations, have a more regular oblong shape, the result of grinding, by
which also a sharp edge has been given to them. The Abbeville tools found
in gravel at different levels, as in Nos. 3 and 4, Fig. 87, in which bones of
the elephant, rhinoceros, and other extinct mammalia occur, are always
unground, having evidently been brought into their present form simply by
the chipping off of fragments of flint by repeated blows, such as could be
given by a stone hammer.
Some of them are oval, others of a spear-headed form, no two exactly
alike, and yet the greater number of each kind are obviously fashioned after
the same general pattern. Their outer surface is often white, the original
black flint having been discoloured and bleached by exposure to the air, or
by the action of acids, as they lay in the gravel. They are most commonly
stained of the same ochreous colour as the flints of the gravel in which they
are imbedded. Occasionally their antiquity is indicated not only by their
colour but by superficial incrustations of carbonate of lime, or by dendrites
formed of oxide of iron and manganese. The edges also of most of them are
worn, sometimes by having been used as tools, or sometimes by having
been rolled in the old river’s bed. They are met with not only in the lower-
level gravels, as in No. 3, Fig. 87, but also in No. 4, or the higher gravels, as
at St. Acheul, in the suburbs of Amiens, where the old alluvium lies at an
elevation of about 100 feet above the level of the river Somme. At both
levels fluviatile and land-shells are met with in the loam as well as in the
gravel, but there are no marine shells associated, except at Abbeville, in the
lowest part of the gravel, near the sea, and a few feet only above the present
high-water mark. Here with fossil shells of living species are mingled the
bones of Elephas primigenius and E. antiquus, Rhinoceros tichorhinus,
Hippopotamus, Felis spelæa, Hyæna spelæa, reindeer, and many others, the
bones accompanying the flint implements in such a manner as to show that
both were buried in the old alluvium at the same period.
Nearly the entire skeleton of a rhinoceros was found at one point,
namely, in the Menchecourt drift at Abbeville, the bones being in such
juxtaposition as to show that the cartilage must have held them together at
the time of their inhumation.

The general absence here and elsewhere of human bones from gravel and
sand in which flint tools are discovered, may in some degree be due to the
present limited extent of our researches. But it may also be presumed that
when a hunter population, always scanty in numbers, ranged over this
region, they were too wary to allow themselves to be overtaken by the
floods which swept away many herbivorous animals from the low river-
plains where they may have been pasturing or sleeping. Beasts of prey
prowling about the same alluvial flats in search of food may also have been
surprised more readily than the human tenant of the same region, to whom
the signs of a coming tempest were better known.
Inundation-mud of Rivers.—Brick-earth.—Fluviatile Loam, or
Loess.—As a general rule, the fluviatile alluvia of different ages (Nos. 2, 3,
4, Fig. 87) are severally made up of coarse materials in their lower portions,
and of fine silt or loam in their upper parts. For rivers are constantly shifting
their position in the valley-plain, encroaching gradually on one bank, near
which there is deep water, and deserting the other or opposite side, where
the channel is growing shallower, being destined eventually to be converted
into land. Where the current runs strongest, coarse gravel is swept along,
and where its velocity is slackened, first sand, and then only the finest mud,
is thrown down. A thin film of this fine sediment is spread, during floods,
over a wide area, on one, or sometimes on both sides, of the main stream,
often reaching as far as the base of the bluffs or higher grounds which
bound the valley. Of such a description are the well-known annual deposits
of the Nile, to which Egypt owes its fertility. So thin are they, that the
aggregate amount accumulated in a century is said rarely to exceed five
inches, although in the course of thousands of years it has attained a vast
thickness, the bottom not having been reached by borings extending to a
depth of 60 feet towards the central parts of the valley. Everywhere it
consists of the same homogeneous mud, destitute of stratification—the only
signs of successive accumulation being where the Nile has silted up its
channel, or where the blown sands of the Libyan desert have invaded the
plain, and give rise to alternate layers of sand and mud.
In European river-loams we occasionally observe isolated pebbles and
angular pieces of stone which have been floated by ice to the places where
they now occur; but no such coarse materials are met with in the plains of
Egypt.

In some parts of the valley of the Rhine the accumulation of similar
loam, called in Germany “loess,” has taken place on an enormous scale. Its
colour is yellowish-grey, and very homogeneous; and Professor Bischoff
has ascertained, by analysis, that it agrees in composition with the mud of
the Nile. Although for the most part unstratified, it betrays in some places
marks of stratification, especially where it contains calcareous concretions,
or in its lower part where it rests on subjacent gravel and sand which
alternate with each other near the junction. About a sixth part of the whole
mass is composed of carbonate of lime, and there is usually an intermixture
of fine quartzose and micaceous sand.
Although this loam of the Rhine is unsolidified, it usually terminates
where it has been undermined by running water in a vertical cliff, from the
face of which shells of terrestrial, fresh-water and amphibious mollusks
project in relief. These shells do not imply the permanent sojourn of a body
of fresh water on the spot, for the most aquatic of them, the Succinea,
inhabits marshes and wet grassy meadows. The Succinea elongata (or S.
oblongata), Fig. 88, is very characteristic both of the loess of the Rhine and
of some other European river-loams.

Among the land-shells of the Rhenish loess, Helix hispida, Fig. 90, and
Pupa muscorum, Fig. 89, are very common. Both the terrestrial and aquatic
shells are of most fragile and delicate structure, and yet they are almost
invariably perfect and uninjured. They must have been broken to pieces had
they been swept along by a violent inundation. Even the colour of some of
the land-shells, as that of Helix nemoralis, is occasionally preserved.
In parts of the valley of the Rhine, between Bingen and Basle, the
fluviatile loam or loess now under consideration is several hundred feet
thick, and contains here and there throughout that thickness land and
amphibious shells. As it is seen in masses fringing both sides of the great
plain, and as occasionally remnants of it occur in the centre of the valley,
forming hills several hundred feet in height, it seems necessary to suppose,
first, a time when it slowly accumulated; and secondly, a later period, when

large portions of it were removed, or when the original valley, which had
been partially filled up with it, was re-excavated.
Such changes may have been brought about by a great movement of
oscillation, consisting first of a general depression of the land, and then of a
gradual re-elevation of the same. The amount of continental depression
which first took place in the interior, must be imagined to have exceeded
that of the region near the sea, in which case the higher part of the great
valley would have its alluvial plain gradually raised by an accumulation of
sediment, which would only cease when the subsidence of the land was at
an end. If the direction of the movement was then reversed, and, during the
re-elevation of the continent, the inland region nearest the mountains should
rise more rapidly than that near the coast, the river would acquire a
denuding power sufficient to enable it to sweep away gradually nearly all
the loam and gravel with which parts of its basin had been filled up.
Terraces and hillocks of mud and sand would then alone remain to attest the
various levels at which the river had thrown down and afterwards removed
alluvial matter.
Cavern Deposits containing Human Remains and Bones of Extinct
Animals.—In England, and in almost all countries where limestone rocks
abound, caverns are found, usually consisting of cavities of large
dimensions, connected together by low, narrow, and sometimes torturous
galleries or tunnels. These subterranean vaults are usually filled in part with
mud, pebbles, and breccia, in which bones occur belonging to the same
assemblage of animals as those characterising the Post-pliocene alluvia
above described. Some of these bones are referable to extinct and others to
living species, and they are occasionally intermingled, as in the valley-
gravels, with implements of one or other of the great divisions of the stone
age, and these are not unfrequently accompanied by human bones, which
are much more common in cavern deposits than in valley-alluvium.
Each suite of caverns, and the passages by which they communicate the
one with the other, afford memorials to the geologist of successive phases
through which they must have passed. First, there was a period when the
carbonate of lime was carried out gradually by springs; secondly, an era
when engulfed rivers or occasional floods swept organic and inorganic
debris into the subterranean hollows previously formed; and thirdly, there
were such changes in the configuration of the region as caused the engulfed

rivers to be turned into new channels, and springs to be dried up, after
which the cave-mud, breccia, gravel, and fossil bones would bear the same
kind of relation to the existing drainage of the country as the older valley-
drifts with their extinct mammalian remains and works of art bear to the
present rivers and alluvial plains.
The quarrying away of large masses of Carboniferous and Devonian
limestone, near Liege, in Belgium, has afforded the geologist magnificent
sections of some of these caverns, and the former communication of
cavities in the interior of the rocks with the old surface of the country by
means of vertical or oblique fissures, has been demonstrated in places
where it would not otherwise have been suspected, so completely have the
upper extremities of these fissures been concealed by superficial drift, while
their lower ends, which extended into the roofs of the caves, are masked by
stalactitic incrustations.
The origin of the stalactite is thus explained by the eminent chemist
Liebig. Mould or humus, being acted on by moisture and air, evolves
carbonic acid, which is dissolved by rain. The rain-water, thus impregnated,
permeates the porous limestone, dissolves a portion of it, and afterwards,
when the excess of carbonic acid evaporates in the caverns, parts with the
calcareous matter, and forms stalactite. Even while caverns are still liable to
be occasionally flooded such calcareous incrustations accumulate, but it is
generally when they are no longer in the line of drainage that a solid floor
of hard stalagmite is formed on the bottom.
The late Dr. Schmerling examined forty caves near Liege, and found in
all of them the remains of the same fauna, comprising the mammoth,
tichorhine rhinoceros, cave-bear, cave-hyæna, cave-lion, and many others,
some of extinct and some of living species, and in all of them flint
implements. In four or five caves only parts of human skeletons were met
with, comprising sometimes skulls with a few other bones, sometimes
nearly every part of the skeleton except the skull. In one of the caves, that
of Engihoul, where Schmerling had found the remains of at least three
human individuals, they were mingled in such a manner with bones of
extinct mammalia, as to leave no doubt on his mind (in 1833) of man
having co-existed with them.
In 1860, Professor Malaise, of Liege, explored with me this same cave of
Engihoul, and beneath a hard floor of stalagmite we found mud full of

bones of extinct and recent animals, such as Schmerling had described, and
my companion, persevering in his researches after I had returned to
England, extracted from the same deposit two human lower jaw-bones
retaining their teeth. The skulls from these Belgian caverns display no
marked deviation from the normal European type of the present day.
The careful investigations carried on by Dr. Falconer, Mr. Pengelly, and
others, in the Brixham cave near Torquay, in 1858, demonstrated that flint
knives were there imbedded in such a manner in loam underlying a floor of
stalagmite as to prove that man had been an inhabitant of that region when
the cave-bear and other members of the ancient post-pliocene fauna were
also in existence.
The absence of gnawed bones had led Dr. Schmerling to infer that none
of the Belgian caves which he explored had served as the dens of wild
beasts; but there are many caves in Germany and England which have
certainly been so inhabited, especially by the extinct hyæna and bear.
A fine example of a hyæna’s den was afforded by the cave of Kirkdale,
so well described by the late Dr. Buckland in his Reliquiæ Diluvianæ. In
that cave, above twenty-five miles north-north-east of York, the remains of
about 300 hyænas, belonging to individuals of every age, were detected.
The species (Hyæna spelæa) has been considered by palæontologists as
extinct; it was larger than the fierce Hyæna crocuta of South Africa, which
it closely resembled, and of which it is regarded by Mr. Boyd Dawkins as a
variety. Dr. Buckland, after carefully examining the spot, proved that the
hyænas must have lived there; a fact attested by the quantity of their dung,
which, as in the case of the living hyæna, is of nearly the same composition
as bone, and almost as durable. In the cave were found the remains of the
ox, young elephant, hippopotamus, rhinoceros, horse, bear, wolf, hare,
water-rat, and several birds. All the bones have the appearance of having
been broken and gnawed by the teeth of the hyænas; and they occur
confusedly mixed in loam or mud, or dispersed through a crust of
stalagmite which covers it. In these and many other cases it is supposed that
portions of herbivorous quadrupeds have been dragged into caverns by
beasts of prey, and have served as their food—an opinion quite consistent
with the known habits of the living hyæna.
Australian Cave-breccias.—Ossiferous breccias are not confined to
Europe, but occur in all parts of the globe; and those discovered in fissures

and caverns in Australia correspond closely in character with what has been
called the bony breccia of the Mediterranean, in which the fragments of
bone and rock are firmly bound together by a red ochreous cement.

Some of these caves were examined by the late Sir T. Mitchell in the
Wellington Valley, about 210 miles west of Sidney, on the river Bell, one of
the principal sources of the Macquarie, and on the Macquarie itself. The
caverns often branch off in different directions through the rock, widening
and contracting their dimensions, and the roofs and floors are covered with
stalactite. The bones are often broken, but do not seem to be water-worn. In
some places they lie imbedded in loose earth, but they are usually included
in a breccia.
The remains belong to marsupial animals. Among the most abundant are
those of the kangaroo, of which there are four species, while others belong
to the genera Phascolomys, the wombat; Dasyurus), the ursine opossum;
Phalangista, the vulpine opossum; and Hypsiprymnus, the kangaroo-rat.

In the fossils above enumerated, several species are larger than the largest
living ones of the same genera now known in Australia. Fig. 91 of the right
side of a lower jaw of a kangaroo (Macropus atlas, Owen) will at once be
seen to exceed in magnitude the corresponding part of the largest living
kangaroo, which is represented in Fig. 92. In both these specimens part of
the substance of the jaw has been broken open, so as to show the permanent
false molar (a, Fig. 91), concealed in the socket. From the fact of this molar
not having been cut, we learn that the individual was young, and had not
shed its first teeth.
The reader will observe that all these extinct quadrupeds of Australia
belong to the marsupial family, or, in other words, that they are referable to
the same peculiar type of organisation which now distinguishes the
Australian mammalia from those of other parts of the globe. This fact is one
of many pointing to a general law deducible from the fossil vertebrate and
invertebrate animals of times immediately antecedent to our own, namely,
that the present geographical distribution of organic forms dates back to a
period anterior to the origin of existing species; in other words, the
limitation of particular genera or families of quadrupeds, mollusca, etc., to
certain existing provinces of land and sea, began before the larger part of
the species now contemporary with man had been introduced into the earth.
Professor Owen, in his excellent “History of British Fossil Mammals,”
has called attention to this law, remarking that the fossil quadrupeds of
Europe and Asia differ from those of Australia or South America. We do not
find, for example, in the Europæo-Asiatic province fossil kangaroos, or
armadillos, but the elephant, rhinoceros, horse, bear, hyæna, beaver, hare,
mole, and others, which still characterise the same continent.
In like manner, in the Pampas of South America the skeletons of
Megatherium, Megalonyx, Glyptodon, Mylodon, Toxodon, Macrauchenia,
and other extinct forms, are analogous to the living sloth, armadillo, cavy,
capybara, and llama. The fossil quadrumana, also associated with some of
these forms in the Brazilian caves, belong to the Platyrrhine family of
monkeys, now peculiar to South America. That the extinct fauna of Buenos
Ayres and Brazil was very modern has been shown by its relation to
deposits of marine shells, agreeing with those now inhabiting the Atlantic.
The law of geographical relationship above alluded to, between the living
vertebrata of every great zoological province and the fossils of the period

immediately antecedent, even where the fossil species are extinct, is by no
means confined to the mammalia. New Zealand, when first examined by
Europeans, was found to contain no indigenous land quadrupeds, no
kangaroos, or opossums, like Australia; but a wingless bird abounded there,
the smallest living representative of the ostrich family, called the Kiwi by
the natives (Apteryx). In the fossils of the Post-pliocene period in this same
island, there is the like absence of kangaroos, opossums, wombats, and the
rest; but in their place a prodigious number of well-preserved specimens of
gigantic birds of the struthious order, called by Owen Dinornis and
Palapteryx, which are entombed in superficial deposits. These genera
comprehended many species, some of which were four, some seven, others
nine, and others eleven feet in height! It seems doubtful whether any
contemporary mammalia shared the land with this population of gigantic
feathered bipeds.
Mr. Darwin, when describing the recent and fossil mammalia of South
America, has dwelt much on the wonderful relationship of the extinct to the
living types in that part of the world, inferring from such geographical
phenomena that the existing species are all related to the extinct ones which
preceded them by a bond of common descent.
Climate of the Post-pliocene Period.—The evidence as to the climate of
Europe during this epoch is somewhat conflicting. The fluviatile and land-
shells are all of existing species, but their geographical range has not always
been the same as at present. Some, for example, which then lived in Britain
are now only found in Norway and Finland, probably implying that the
Post-pliocene climate of Britain was colder, especially in the winter. So also
the reindeer and the musk-ox (Ovibos moschatus), now inhabitants of the
Arctic regions, occur fossil in the valleys of the Thames and Avon, and also
in France and Germany, accompanied in most places by the mammoth and
the woolly rhinoceros. At Grays in Essex, on the other hand, another species
both of elephant and rhinoceros occurs, together with a hippopotamus and
the Cyrena fluminalis, a shell now extinct in Europe but still an inhabitant
of the Nile and some Asiatic rivers. With it occurs the Unio littoralis, now
living in the Seine and Loire. In the valley of the Somme flint tools have
been found associated with Hippopotamus major and Cyrena fluminalis in
the lower-level Post-pliocene gravels; while in the higher-level (and more
ancient) gravels similar tools are more abundant, and are associated with

the bones of the mammoth and other Post-pliocene quadrupeds indicative of
a colder climate.
It is possible that we may here have evidence of summer and winter
migrations rather than of a general change of temperature. Instead of
imagining that the hippopotamus lived all the year round with the musk-ox
and lemming, we may rather suppose that the apparently conflicting
evidence may be due to the place of our observations being near the
boundary line of a northern and southern fauna, either of which may have
advanced or receded during comparatively slight and temporary
fluctuations of climate. There may then have been a continuous land
communication between England and the North of Siberia, as well as in an
opposite direction with Africa, then united to Southern Europe.
In drift at Fisherton, near Salisbury, thirty feet above the river Wiley, the
Greenland lemming and a new species of the Arctic genus Spermophilus
have been found, along with the mammoth, reindeer, cave-hyæna, and other
mammalia suited to a cold climate. A flint implement was taken out from
beneath the bones of the mammoth. In a higher and older deposit in the
vicinity, flint tools like those of Amiens have been discovered. Nearly all
the known Post-pliocene quadrupeds have now been found accompanying
flint knives or hatchets in such a way as to imply their coexistence with
man; and we have thus the concurrent testimony of several classes of
geological facts to the vast antiquity of the human race. In the first place,
the disappearance of a great variety of species of wild animals from every
part of a wide continent must have required a vast period for its
accomplishment; yet this took place while man existed upon the earth, and
was completed before that early period when the Danish shell-mounds were
formed or the oldest of the Swiss lake-dwellings constructed. Secondly, the
deepening and widening of valleys, indicated by the position of the river
gravels at various heights, implies an amount of change of which that which
has occurred during the historical period forms a scarcely perceptible part.
Thirdly, the change in the course of rivers which once flowed through caves
now removed from any line of drainage, and the formation of solid floors of
stalagmite, must have required a great lapse of time. Lastly, ages must have
been required to change the climate of wide regions to such an extent as
completely to alter the geographical distribution of many mammalia as well
as land and fresh-water shells. The 3000 or 4000 years of the historical
period does not furnish us with any appreciable measure for calculating the

number of centuries which would suffice for such a series of changes,
which are by no means of a local character, but have operated over a
considerable part of Europe.
Relative Longevity of Species in the Mammalia and Testacea.—I
called attention in 1830[5] to the fact, which had not at that time attracted
notice, that the association in the Post-pliocene deposits of shells,
exclusively of living species, with many extinct quadrupeds betokened a
longevity of species in the testacea far exceeding that in the mammalia.
Subsequent researches seem to show that this greater duration of the same
specific forms in the class mollusca is dependent on a still more general
law, namely, that the lower the grade of animals, or the greater the
simplicity of their structure, the more persistent are they in general in their
specific characters throughout vast periods of time. Not only have the
invertebrata, as shown by geological data, altered at a less rapid rate than
the vertebrata, but if we take one of the classes of the former, as for
example the mollusca, we find those of more simple structure to have
varied at a slower rate than those of a higher and more complex
organisation; the Brachiopoda, for example, more slowly than the
lamellibranchiate bivalves, while the latter have been more persistent than
the univalves, whether gasteropoda or cephalopoda. In like manner the
specific identity of the characters of the foraminifera, which are among the
lowest types of the invertebrata, has outlasted that of the mollusca in an
equally decided manner.
Teeth of Post-pliocene Mammalia.—To those who have never studied
comparative anatomy, it may seem scarcely credible that a single bone
taken from any part of the skeleton may enable a skilful osteologist to
distinguish, in many cases, the genus, and sometimes the species, of
quadrupeds to which it belonged. Although few geologists can aspire to
such knowledge, which must be the result of long practice and study, they
will nevertheless derive great advantage from learning, what is
comparatively an easy task, to distinguish the principal divisions of the
mammalia by the forms and characters of their teeth.

Figures 93 through 105 represent the teeth of some of the more common
species and genera found in alluvial and cavern deposits.

On comparing the grinding surfaces of the corresponding molars of the
three species of elephants, Figs. 93, 94, 95 it will be seen that the folds of
enamel are most numerous in the mammoth, fewer and wider, or more
open, in E. antiquus; and most open and fewest in E. meridionalis. It will be
also seen that the enamel in the molar of the Rhinoceros tichorhinus (Fig.
97), is much thicker than in that of the Rhinoceros leptorhinus (Fig. 96).
[1] Sir John Lubbock, Pre-historic Times, p. 3, 1865.

[2] Bulletin de la Sociétié Vaudoise des Sci. Nat., tome vi, Lausanne 1860; and
Antiquity of Man, by the author, chap. ii.

[3] Sir J. Lubbock’s Lecture, Royal Institution, Feb. 27th, 1863.

[4] Diodorus, v, 21, 22 and Sir H. James Note on Block of Tin dredged up in
Falmouth Harbour. Royal Institution of Cornwall, 1863.

[5] Principles of Geology, 1st ed., vol. iii, p. 140.

CHAPTER XI.
POST-PLIOCENE PERIOD, continued—GLACIAL
[1]
CONDITIONS.

Geographical Distribution, Form, and Characters of Glacial
Drift. — Fundamental Rocks, polished, grooved, and
scratched. — Abrading and striating Action of Glaciers. —
Moraines, Erratic Blocks, and “Roches Moutonnees.” Alpine
Blocks on the Jura. — Continental Ice of Greenland. —
Ancient Centres of the Dispersion of Erratics. —
Transportation of Drift by floating Icebergs. — Bed of the
Sea furrowed and polished by the running aground of
floating Ice-islands.

Character and Distribution of Glacial Drift.—In speaking of the loose
transported matter commonly found on the surface of the land in all parts of
the globe, I alluded to the exceptional character of what has been called the
boulder formation in the temperate and Arctic latitudes of the northern
hemisphere. The peculiarity of its form in Europe north of the 50th, and in
North America north of the 40th parallel of latitude, is now universally
attributed to the action of ice, and the difference of opinion respecting it is
now chiefly restricted to the question whether land-ice or floating icebergs
have played the chief part in its distribution. It is wanting in the warmer and
equatorial regions, and reappears when we examine the lands which lie
south of the 40th and 50th parallels in the southern hemisphere, as, for
example, in Patagonia, Tierra del Fuego, and New Zealand. It consists of
sand and clay, sometimes stratified, but often wholly devoid of stratification
for a depth of 50, 100, or even a greater number of feet. To this unstratified
form of the deposit the name of till has long been applied in Scotland. It
generally contains a mixture of angular and rounded fragments of rock,

some of large size, having occasionally one or more of their sides flattened
and smoothed, or even highly polished. The smoothed surfaces usually
exhibit many scratches parallel to each other, one set of which often crosses
an older set. The till is almost everywhere wholly devoid of organic
remains, except those washed into it from older formations, though in some
places it contains marine shells, usually of northern or Arctic species, and
frequently in a fragmentary state. The bulk of the till has usually been
derived from the grinding down into mud of rocks in the immediate
neighbourhood, so that it is red in a region of Red Sandstone, as in
Strathmore in Forfarshire; grey or black in a district of coal and bituminous
shale, as around Edinburgh; and white in a chalk country, as in parts of
Norfolk and Denmark. The stony fragments dispersed irregularly through
the till usually belong, especially in mountainous countries, to rocks found
in some part of the same hydrographical basin; but there are regions where
the whole of the boulder clay has come from a distance, and huge blocks, or
“erratics,” as they have been called, many feet in diameter, have not
unfrequently travelled hundreds of miles from their point of departure, or
from the parent rocks from which they have evidently been detached. These
are commonly angular, and have often one or more of their sides polished
and furrowed.
The rock on which the boulder formation reposes, if it consists of granite,
gneiss, marble, or other hard stone, capable of permanently retaining any
superficial markings which may have been imprinted upon it, is usually
smoothed or polished, like the erratics above described, and exhibits
parallel striæ and furrows having a determinate direction. This direction,
both in Europe and North America, agrees generally in a marked manner
with the course taken by the erratic blocks in the same district. The boulder
clay, when it was first studied, seemed in many of its characters so singular
and anomalous, that geologists despaired of ever being able to interpret the
phenomena by reference to causes now in action. In those exceptional cases
where marine shells of the same date as the boulder clay were found, nearly
all of them were recognised as living species—a fact conspiring with the
superficial position of the drift to indicate a comparatively modern origin.
The term “diluvium” was for a time the most popular name of the
boulder formation, because it was referred by many to the deluge of Noah,
while others retained the name as expressive of their opinion that a series of
diluvial waves raised by hurricanes and storms, or by earthquakes, or by the

sudden upheaval of land from the bed of the sea, had swept over the
continents, carrying with them vast masses of mud and heavy stones, and
forcing these stones over rocky surfaces so as to polish and imprint upon
them long furrows and striæ. But geologists were not long in seeing that the
boulder formation was characteristic of high latitudes, and that on the whole
the size and number of erratic blocks increases as we travel towards the
Arctic regions. They could not fail to be struck with the contrast which the
countries bordering the Baltic presented when compared with those
surrounding the Mediterranean. The multitude of travelled blocks and
striated rocks in the one region, and the absence of such appearances in the
other, were too obvious to be overlooked. Even the great development of
the boulder formation, with large erratics so far south as the Alps, offered
an exception to the general rule favourable to the hypothesis that there was
some intimate connection between it and accumulations of snow and ice.

Transporting and abrading Power of Glaciers.—I have described
elsewhere (“Principles” vol. i, chap. xvi, 1867) the manner in which the
snow of the Alpine heights is prevented from accumulating indefinitely in
thickness by the constant descent of a large portion of it by gravitation.
Becoming converted into ice it forms what are termed glaciers, which glide
down the principal valleys. On their surface are seen mounds of rubbish or

large heaps of sand and mud, with angular fragments of rock which fall
from the steep slopes or precipices bounding the glaciers. When a glacier,
thus laden, descends so far as to reach a region about 3500 feet above the
level of the sea, the warmth of the air is such that it melts rapidly in
summer, and all the mud, sand, and pieces of rock are slowly deposited at
its lower end, forming a confused heap of unstratified rubbish called a
moraine, and resembling the till before described (p. 166).
Besides the blocks thus carried down on the top of the glacier, many fall
through fissures in the ice to the bottom, where some of them become
firmly frozen into the mass, and are pushed along the base of the glacier,
abrading, polishing, and grooving the rocky floor below, as a diamond cuts
glass, or as emery-powder polishes steel. The striæ which are made, and the
deep grooves which are scooped out by this action, are rectilinear and
parallel to an extent never seen in those produced on loose stones or rocks,
where shingle is hurried along by a torrent, or by the waves on a sea-beach.
In addition to these polished, striated, and grooved surfaces of rock, another
mark of the former action of a glacier is the “roche moutonnee.” Projecting
eminences of rock so called have been smoothed and worn into the shape of
flattened domes by the glacier as it passed over them. They have been
traced in the Alps to great heights above the present glaciers, and to great
horizontal distances beyond them.
Alpine Blocks on the Jura.—The moraines, erratics, polished surfaces,
domes, and striæ, above described, are observed in the great valley of
Switzerland, fifty miles broad; and almost everywhere on the Jura, a chain
which lies to the north of this valley. The average height of the Jura is about
one-third that of the Alps, and it is now entirely destitute of glaciers; yet it
presents almost everywhere similar moraines, and the same polished and
grooved surfaces. The erratics, moreover, which cover it, present a
phenomenon which has astonished and perplexed the geologist for more
than half a century. No conclusion can be more incontestable than that these
angular blocks of granite, gneiss, and other crystalline formations came
from the Alps, and that they have been brought for a distance of fifty miles
and upward across one of the widest and deepest valleys in the world; so
that they are now lodged on a chain composed of limestone and other
formations, altogether distinct from those of the Alps. Their great size and
angularity, after a journey of so many leagues, has justly excited wonder;
for hundreds of them are as large as cottages; and one in particular,

composed of gneiss, celebrated under the name of Pierre à Bot, rests on the
side of a hill about 900 feet above the lake of Neufchâtel, and is no less than
40 feet in diameter.
In the year 1821, M. Venetz first announced his opinion that the Alpine
glaciers must formerly have extended far beyond their present limits, and
the proofs appealed to by him in confirmation of this doctrine were
acknowledged by all subsequent observers, and greatly strengthened by
new observations and arguments. M. Charpentier supposed that when the
glaciers extended continuously from the Alps to the Jura, the former
mountains were 2000 or 3000 feet higher than at present. Other writers, on
the contrary, conjectured that the whole country had been submerged, and
the moraines and erratic blocks transported on floating icebergs; but a
careful study of the distribution of the travelled masses, and the total
absence of marine shells from the old glacial drift of Switzerland, have
entirely disproved this last hypothesis. In addition to the many evidences of
the action of ice in the northern parts of Europe which we have already
mentioned, there occur here and there in some of these countries, what are
wanting in Switzerland, deposits of marine fossil shells, which exhibit so
arctic a character that they must have led the geologist to infer the former
prevalence of a much colder climate, even had he not encountered so many
accompanying signs of ice-action. The same marine shells demonstrate the
submergence of large areas in Scandinavia and the British Isles, during the
glacial cold.
A characteristic feature of the deposits under consideration in all these
countries is the occurrence of large erratic blocks, and sometimes of
moraine matter, in situations remote from lofty mountains, and separated
from the nearest points where the parent rocks appear at the surface by great
intervening valleys, or arms of the sea. We also often observe striæ and
furrows, as in Norway, Sweden, and Scotland, which deviate from the
direction which they ought to follow if they had been connected with the
present line of drainage, and they, therefore, imply the prevalence of a very
distinct condition of things at the time when the cold was most intense. The
actual state of North Greenland seems to afford the best explanation of such
abnormal glacial markings.
Greenland Continental Ice.—Greenland is a vast unexplored continent,
buried under one continuous and colossal mass of ice that is always moving

seaward, a very small part of it in an easterly direction, and all the rest
westward, or towards Baffin’s Bay. All the minor ridges and valleys are
levelled and concealed under a general covering of snow, but here and there
some steep mountains protrude abruptly from the icy slope, and a few
superficial lines of stones or moraines are visible at certain seasons, when
no snow has fallen for many months, and when evaporation, promoted by
the wind and sun, has caused much of the upper snow to disappear. The
height of this continent is unknown, but it must be very great, as the most
elevated lands of the outskirts, which are described as comparatively low,
attain altitudes of 4000 to 6000 feet. The icy slope gradually lowers itself
towards the outskirts, and then terminates abruptly in a mass about 2000
feet in thickness, the great discharge of ice taking place through certain
large friths, which, at their upper ends, are usually about four miles across.
Down these friths the ice is protruded in huge masses, several miles wide,
which continue their course—grating along the rocky bottom like ordinary
glaciers long after they have reached the salt water. When at last they arrive
at parts of Baffin’s Bay deep enough to buoy up icebergs from 1000 to 1500
feet in vertical thickness, broken masses of them float off, carrying with
them on their surface not only fine mud and sand but large stones. These
fragments of rock are often polished and scored on one or more sides, and
as the ice melts, they drop down to the bottom of the sea, where large
quantities of mud are deposited, and this muddy bottom is inhabited by
many mollusca.
Although the direction of the ice-streams in Greenland may coincide in
the main with that which separate glaciers would take if there were no more
ice than there is now in the Swiss Alps, yet the striation of the surface of the
rocks on an ice-clad continent would, on the whole, vary considerably in its
minor details from that which would be imprinted on rocks constituting a
region of separate glaciers. For where there is a universal covering of ice
there will be a general outward movement from the higher and more central
regions towards the circumference and lower country, and this movement
will be, to a certain extent, independent of the minor inequalities of hill and
valley, when these are all reduced to one level by the snow. The moving ice
may sometimes cross even at right angles deep narrow ravines, or the crests
of buried ridges, on which last it may afterwards seem strange to detect
glacial striæ and polishing after the liquefaction of the snow and ice has
taken place.

Rink mentions that in North Greenland powerful springs of clayey water
escape in winter from under the ice, where it descends to “the outskirts,”
and where, as already stated, it is often 2000 feet thick—a fact showing
how much grinding action is going on upon the surface of the subjacent
rocks. I also learn from Dr. Torell that there are large areas in the outskirts,
now no longer covered with permanent snow or glaciers, which exhibit on
their surface unmistakable signs of ancient ice-action, so that, vast as is the
power now exerted by ice in Greenland, it must once have operated on a
still grander scale. The land, though now very elevated, may perhaps have
been formerly much higher. It is well-known that the south coast of
Greenland, from latitude 60° to about 70° N., has for the last four centuries
been sinking at the rate of several feet in a century. By this means a surface
of rock, well scored and polished by ice, is now slowly subsiding beneath
the sea, and is becoming strewed over, as the icebergs melt, with impalpable
mud and smoothed and scratched stones. It is not precisely known how far
north this downward movement extends.
Drift carried by Icebergs.—An account was given so long ago as the
year 1822, by Scoresby, of icebergs seen by him in the Arctic seas drifting
along in latitudes 69° and 70° N., which rose above the surface from 100 to
200 feet, and some of which measured a mile in circumference. Many of
them were loaded with beds of earth and rock, of such thickness that the
weight was conjectured to be from 50,000 to 100,000 tons. A similar
transportation of rocks is known to be in progress in the southern
hemisphere, where boulders included in ice are far more frequent than in
the north. One of these icebergs was encountered in 1839, in mid-ocean, in
the antarctic regions, many hundred miles from any known land, sailing
northward, with a large erratic block firmly frozen into it. Many of them,
carefully measured by the officers of the French exploring expedition of the
Astrolabe, were between 100 and 225 feet high above water, and from two
to five miles in length. Captain d’Urville ascertained one of them which he
saw floating in the Southern Ocean to be 13 miles long and 100 feet high,
with walls perfectly vertical. The submerged portions of such islands must,
according to the weight of ice relatively to sea-water, be from six to eight
times more considerable than the part which is visible, so that when they
are once fairly set in motion, the mechanical force which they might exert
against any obstacle standing in their way would be prodigious.

We learn, therefore, from a study both of the arctic and antarctic regions,
that a great extent of land may be entirely covered throughout the whole
year by snow and ice, from the summits of the loftiest mountains to the sea-
coast, and may yet send down angular erratics to the ocean. We may also
conclude that such land will become in the course of ages almost
everywhere scored and polished like the rocks which underlie a glacier. The
discharge of ice into the surrounding sea will take place principally through
the main valleys, although these are hidden from our sight. Erratic blocks
and moraine matter will be dispersed somewhat irregularly after reaching
the sea, for not only will prevailing winds and marine currents govern the
distribution of the drift, but the shape of the submerged area will have its
influence; inasmuch as floating ice, laden with stones, will pass freely
through deep water, while it will run a ground where there are reefs and
shallows. Some icebergs in Baffin’s Bay have been seen stranded on a
bottom 1000 or even 1500 feet deep. In the course of ages such a sea-bed
may become densely covered with transported matter, from which some of
the adjoining greater depths may be free. If, as in West Greenland, the land
is slowly sinking, a large extent of the bottom of the ocean will consist of
rock polished and striated by land-ice, and then overspread by mud and
boulders detached from melting bergs.
The mud, sand, and boulders thus let fall in still water must be exactly
like the moraines of terrestrial glaciers, devoid of stratification and organic
remains. But occasionally, on the outer side of such packs of stranded bergs,
the waves and currents may cause the detached earthy and stony materials
to be sorted according to size and weight before they reach the bottom, and
to acquire a stratified arrangement.
I have already alluded (p. 172) to the large quantity of ice, containing
great blocks of stone, which is sometimes seen floating far from land, in the
southern or Antarctic seas. After the emergence, therefore, of such a
submarine area, the superficial detritus will have no necessary relation to
the hills, valleys, and river-plains over which it will be scattered. Many a
water-shed may intervene between the starting-point of each erratic or
pebble and its final resting-place, and the only means of discovering the
country from which it took its departure will consist in a careful comparison
of its mineral or fossil contents with those of the parent rocks.
[1] As to the former excess of cold, whether brought about by modifications in
the height and distribution of the land or by altered astronomical conditions, see

Principles, vol. i, (10th ed., 1867), chaps. xii and xiii, “Vicissitudes of Climate.”

CHAPTER XII.
POST-PLIOCENE PERIOD, continued.—GLACIAL
CONDITIONS, concluded.

Glaciation of Scandinavia and Russia. — Glaciation of
Scotland. — Mammoth in Scotch Till. — Marine Shells in
Scotch Glacial Drift. — Their Arctic Character. — Rarity of
Organic Remains in Glacial Deposits. — Contorted Strata in
Drift. — Glaciation of Wales, England, and Ireland. —
Marine Shells of Moel Tryfaen. — Erratics near Chichester.
— Glacial Formations of North America. — Many Species
of Testacea and Quadrupeds survived the Glacial Cold. —
Connection of the Predominance of Lakes with Glacial
Action. — Action of Ice in preventing the silting up of Lake-
basins. — Absence of Lakes in the Caucasus. — Equatorial
Lakes of Africa.

Glaciation of Scandinavia and Russia.—In large tracts of Norway and
Sweden, where there have been no glaciers in historical times, the signs of
ice-action have been traced as high as 6000 feet above the level of the sea.
These signs consist chiefly of polished and furrowed rock-surfaces, of
moraines and erratic blocks. The direction of the erratics, like that of the
furrows, has usually been conformable to the course of the principal
valleys; but the lines of both sometimes radiate outward in all directions
from the highest land, in a manner which is only explicable by the
hypothesis above alluded to of a general envelope of continental ice, like
that of Greenland (page 170). Some of the far-transported blocks have been
carried from the central parts of Scandinavia towards the Polar regions;
others southward to Denmark; some south-westward, to the coast of

Norfolk in England; others south-eastward, to Germany, Poland, and
Russia.
In the immediate neighbourhood of Upsala, in Sweden, I had observed,
in 1834, a ridge of stratified sand and gravel, in the midst of which occurs a
layer of marl, evidently formed originally at the bottom of the Baltic, by the
slow growth of the mussel, cockle, and other marine shells of living species,
intermixed with some proper to fresh water. The marine shells are all of
dwarfish size, like those now inhabiting the brackish waters of the Baltic;
and the marl, in which many of them are imbedded, is now raised more than
100 feet above the level of the Gulf of Bothnia. Upon the top of this ridge
repose several huge erratics, consisting of gneiss for the most part
unrounded, from nine to sixteen feet in diameter, and which must have been
brought into their present position since the time when the neighbouring
gulf was already characterised by its peculiar fauna. Here, therefore, we
have proof that the transport of erratics continued to take place, not merely
when the sea was inhabited by the existing testacea, but when the north of
Europe had already assumed that remarkable feature of its physical
geography which separates the Baltic from the North Sea, and causes the
Gulf of Bothnia to have only one-fourth of the saltness belonging to the
ocean. In Denmark, also, recent shells have been found in stratified beds,
closely associated with the boulder clay.
Glaciation of Scotland.—Mr. T. F. Jamieson, in 1858, adduced a great
body of facts to prove that the Grampians once sent down glaciers from the
central regions in all directions towards the sea. “The glacial grooves,” he
observed, “radiate outward from the central heights towards all points of the
compass, though they do not always strictly conform to the actual shape and
contour of the minor valleys and ridges.”
These facts and other characteristics of the Scotch drift lead us to the
inference that when the glacial cold first set in, Scotland stood higher above
the sea than at present, and was covered for the most part with snow and
ice, as Greenland is now. This sheet of land-ice sliding down to lower
levels, ground down and polished the subjacent rocks, sweeping off nearly
all superficial deposits of older date, and leaving only till and boulders in
their place. To this continental state succeeded a period of depression and
partial submergence. The sea advanced over the lower lands, and Scotland
was converted into an archipelago, some marine sand with shells being

spread over the bottom of the sea. On this sand a great mass of boulder clay
usually quite devoid of fossils was accumulated. Lastly, the land re-emerged
from the water, and, reaching a level somewhat above its present height,
became connected with the continent of Europe, glaciers being formed once
more in the higher regions, though the ice probably never regained its
former extension.[1] After all these changes, there were some minor
oscillations in the level of the land, on which, although they have had
important geographical consequences, separating Ireland from England, for
example, and England from the Continent, we need not here enlarge.
Mammoth in Scotch Till.—Almost all remains of the terrestrial fauna of
the Continent which preceded the period of submergence have been lost;
but a few patches of estuarine and fresh-water formations escaped
denudation by submergence. To these belong the peaty clay from which
several mammoths’ tusks and horns of reindeer were obtained at Kilmaurs,
in Ayrshire as long ago as 1816. Mr. Bryce in 1865 ascertained that the
fresh-water formation containing these fossils rests on carboniferous
sandstone, and is covered, first by a bed of marine sand with arctic shells,
and then with a great mass of till with glaciated boulders.[2] Still more recent
explorations in the neighbourhood of Kilmaurs have shown that the fresh-
water formation contains the seed of the pond-weed Potamogeton and the
aquatic Ranunculus; and Mr. Young of the Glasgow Museum washed the
mud adhering to the reindeer horns of Kilmaurs and that which filled the
cracks of the associated elephants’ tusks, and detected in these fossils
(which had been in the Glasgow Museum for half a century) abundance of
the same seeds.
All doubts, therefore, as to the true position of the remains of the
mammoth, a fossil so rare in Scotland, have been set at rest, and it serves to
prove that part of the ancient continent sank beneath the sea at a period of
great cold, as the shells of the overlying sand attest. The incumbent till or
boulder clay is about 40 feet thick, but it often attains much greater
thickness in the same part of Scotland.

Marine Shells of Scotch Drift.—The greatest height to which marine
shells have yet been traced in this boulder clay is at Airdie, in Lanarkshire,
ten miles east of Glasgow, 524 feet above the level of the sea. At that spot
they were found imbedded in stratified clays with till above and below
them. There appears no doubt that the overlying deposit was true glacial till,
as some boulders of granite were observed in it, which must have come
from distances of sixty miles at the least.

The shells figured in Figs. 107 to 112 are only a few out of a large
assemblage of living species, which, taken as a whole, bear testimony to
conditions far more arctic than those now prevailing in the Scottish seas.
But a group of marine shells, indicating a still greater excess of cold, has
been brought to light since 1860 by the Reverend Thomas Brown, from
glacial drift or clay on the borders of the estuaries of the Forth and Tay. This
clay occurs at Elie, in Fife, and at Errol, in Perthshire; and has already
afforded about 35 shells, all of living species, and now inhabitants of arctic
regions, such as Leda truncata, Tellina proxima (see Figs. 113 and 114),

Pecten Grœnlandicus, Crenella lævigata, Crenella nigra, and others, some
of them first brought by Captain Sir E. Parry from the coast of Melville
Island, latitude 76° N. These were all identified in 1863 by Dr. Torell, who
had just returned from a survey of the seas around Spitzbergen, where he
had collected no less than 150 species of mollusca, living chiefly on a
bottom of fine mud derived from the moraines of melting glaciers which
there protrude into the sea. He informed me that the fossil fauna of this
Scotch glacial deposit exhibits not only the species but also the peculiar
varieties of mollusca now characteristic of very high latitudes. Their large
size implies that they formerly enjoyed a colder, or, what was to them a
more genial climate, than that now prevailing in the latitude where the
fossils occur. Marine shells have also been found in the glacial drift of
Caithness and Aberdeenshire at heights of 250 feet, and in Banff of 350
feet, and stratified drift continuous with the above ascends to heights of 500
feet. Already 75 species are enumerated from Caithness, and the same
number from Aberdeenshire and Banff, and in both cases all but six are
arctic species.
I formerly suggested that the absence of all signs of organic life in the
Scotch drift might be connected with the severity of the cold, and also in
some places with the depth of the sea during the period of extreme
submergence; but my faith in such an hypothesis has been shaken by
modern investigations, an exuberance of life having been observed both in
arctic and antarctic seas of great depth, and where floating ice abounds. The
difficulty, moreover, of accounting for the entire dearth of marine shells in
till is removed when once we have adopted the theory of this boulder clay
being the product of land-ice. For glaciers coming down from a continental
ice-sheet like that which covers Greenland may fill friths many hundred feet
below the sea-level, and even invade parts of a bay a thousand feet deep,
before they find water enough to float off their terminal portions in the form
of icebergs. In such a case till without marine shells may first accumulate,
and then, if the climate becomes warmer and the ice melts, a marine deposit
may be superimposed on the till without any change of level being required.
Another curious phenomenon bearing on this subject was styled by the
late Hugh Miller the “striated pavements” of the boulder clay. Where
portions of the till have been removed by the sea on the shores of the Forth,
or in the interior by railway cuttings, the boulders imbedded in what
remains of the drift are seen to have been all subjected to a process of

abrasion and striation, the striæ and furrows being parallel and persistent
across them all, exactly as if a glacier or iceberg had passed over them and
scored them in a manner similar to that so often undergone by the solid
rocks below the glacial drift. It is possible, as Mr. Geikie conjectures, that
this second striation of the boulders may be referable to floating ice.[3]
Contorted Strata in Drift.—In Scotland the till is often covered with
stratified gravel, sand, and clay, the beds of which are sometimes horizontal
and sometimes contorted for a thickness of several feet. Such contortions
are not uncommon in Forfarshire, where I observed them, among other
places, in a vertical cutting made in 1840 near the left bank of the South
Esk, east of the bridge of Cortachie. The convolutions of the beds of fine
and coarse sand, gravel, and loam, extend through a thickness of no less
than 25 feet vertical, or from b to c, Fig. 115, the horizontal stratification
being resumed very abruptly at a short distance, as to the right of f, g. The
overlying coarse gravel and sand, a, is in some places horizontal, in others
it exhibits cross bedding, and does not partake of the disturbances which the
strata b, c, have undergone. The underlying till is exposed for a depth of
about 20 feet; and we may infer from sections in the neighbourhood that it
is considerably thicker.

In some cases I have seen fragments of stratified clays and sands, bent in
like manner, in the middle of a great mass of till. Mr. Trimmer has
suggested, in explanation of such phenomena, the intercalation in the
glacial period of large irregular masses of snow or ice between layers of
sand and gravel. Some of the cliffs near Behring’s Straits, in which the
remains of elephants occur, consist of ice mixed with mud and stones; and
Middendorf describes the occurrence in Siberia of masses of ice, found at
various depths from the surface after digging through drift. Whenever the

intercalation of snow and ice with drift, whether stratified or unstratified,
has taken place, the melting of the ice will cause such a failure of support as
may give rise to flexures, and sometimes to the most complicated foldings.
But in many cases the strata may have been bent and deranged by the
mechanical pressure of an advancing glacier, or by the sideway thrust of
huge islands of ice running aground against sandbanks; in which case, the
position of the beds forming the foundation of the banks may not be at all
disturbed by the shock.
There are indeed many signs in Scotland of the action of floating ice, as
might have been expected where proofs of submergence in the Glacial
Period are not wanting. Among these are the occurrence of large erratic
blocks, frequently in clusters at or near the tops of hills or ridges, places
which may have formed islets or shallows in the sea where floating ice
would mostly ground and discharge its cargo on melting. Glaciers or land-
ice would, on the contrary, chiefly discharge their cargoes at the bottom of
valleys. Traces of an earlier and independent glaciation have also been
observed in some regions where the striation, apparently produced by ice
proceeding from the north-west, is not explicable by the radiation of land-
ice from a central mountainous region.[4]
Glaciation of Wales and England.—The mountains of North Wales
were recognised, in 1842, by Dr. Buckland, as having been an independent
centre of the dispersion of erratics—great glaciers, long since extinct,
having radiated from the Snowdonian heights in Carnarvonshire, through
seven principal valleys towards as many points of the compass, carrying
with them large stony fragments, and grooving the subjacent rocks in as
many directions.
Besides this evidence of land-glaciers, Mr. Trimmer had previously, in
1831, detected the signs of a great submergence in Wales in the Post-
pliocene period. He had observed stratified drift, from which he obtained
about a dozen species of marine shells, near the summit of Moel Tryfaen, a
hill 1400 feet high, on the south side of the Menai Straits. I had an
opportunity of examining in the summer of 1863, together with the
Reverend W. S. Symonds, a long and deep cutting made through this drift
by the Alexandra Mining Company in search of slates. At the top of the hill
above-mentioned we saw a stratified mass of incoherent sand and gravel 35
feet thick, from which no less than 54 species of mollusca, besides three

characteristic arctic varieties—in all 57 forms—have been obtained by Mr.
Darbishire. They belong without exception to species still living in British
or more northern seas; eleven of them being exclusively arctic, four
common to the arctic and British seas, and a large proportion of the
remainder having a northward range, or, if found at all in the southern seas
of Britain, being comparatively less abundant. In the lowest beds of the drift
were large heavy boulders of far-transported rocks, glacially polished and
scratched on more than one side. Underneath the whole we saw the edges of
vertical slates exposed to view, which here, like the rocks in other parts of
Wales, both at greater and less elevations, exhibit beneath the drift
unequivocal marks of prolonged glaciation. The whole deposit has much
the appearance of an accumulation in shallow water or on a beach, and it
probably acquired its thickness during the gradual subsidence of the coast—
an hypothesis which would require us to ascribe to it a high antiquity, since
we must allow time, first for its sinking, and then for its re-elevation.
The height reached by these fossil shells on Moel Tryfaen is no less than
1300 feet—a most important fact when we consider how very few instances
we have on record beyond the limits of Wales, whether in Europe or North
America, of marine shells having been found in glacial drift at half the
height above indicated. A marine molluscous fauna, however, agreeing in
character with that of Moel Tryfaen, and comprising as many species, has
been found in drift at Macclesfield and other places in central England,
sometimes reaching an elevation of 1200 feet.
Professor Ramsay[5] estimated the probable amount of submergence
during some part of the glacial period at about 2300 feet; for he was unable
to distinguish the superficial sands and gravel which reached that high
elevation from the drift which, at Moel Tryfaen and at lower points,
contains shells of living species. The evidence of the marine origin of the
highest drift is no doubt inconclusive in the absence of shells, so great is the
resemblance of the gravel and sand of a sea beach and of a river’s bed,
when organic remains are wanting; but, on the other hand, when we
consider the general rarity of shells in drift which we know to be of marine
origin, we cannot suppose that, in the shelly sands of Moel Tryfaen, we
have hit upon the exact uppermost limit of marine deposition, or, in other
words, a precise measure of the submergence of the land beneath the sea
since the glacial period.

We are gradually obtaining proofs of the larger part of England, north of
a line drawn from the mouth of the Thames to the Bristol Channel, having
been under the sea and traversed by floating ice since the commencement of
the glacial epoch. Among recent observations illustrative of this point, I
may allude to the discovery, by Mr. J. F. Bateman, near Blackpool, in
Lancashire, fifty miles from the sea, and at the height of 568 feet above its
level, of till containing rounded and angular stones and marine shells, such
as Turritella communis, Purpura lapillus, Cardium edule, and others,
among which Trophon clathratum (=Fusus Bamffius), though still surviving
in North British seas, indicates a cold climate.
Erratics near Chichester.—The most southern memorials of ice-action
and of a Post-pliocene fauna in Great Britain is on the coast of the county of
Sussex, about 25 miles west of Brighton, and 15 south of Chichester. A
marine deposit exposed between high and low tide occurs on both sides of
the promontory called Selsea Bill, in which Mr. Godwin-Austen found
thirty-eight species of shells, and the number has since been raised to
seventy.
This assemblage is interesting because on the whole, while all the species
are recent, they have a somewhat more southern aspect than those of the
present British Channel. It is true that about forty of them range from
British to high northern latitudes; but several of them, as, for example,
Lutraria rugosa and Pecten polymorphous, which are abundant, are not
known at present to range farther north than the coast of Portugal, and seem
to indicate a warmer temperature than now prevails on the coast where we
find them fossil. What renders this curious is the fact that the sandy loam in
which they occur is overlaid by yellow clayey gravel with large erratic
blocks which must have been drifted into their present position by ice when
the climate had become much colder. These transported fragments of
granite, syenite, and greenstone, as well as of Devonian and Silurian rocks,
may have come from the coast of Normandy and Brittany, and are many of
them of such large size that we must suppose them to have been drifted into
their present site by coast-ice. I measured one of granite, at Pagham, 21 feet
in circumference. In the gravel of this drift with erratics are a few littoral
shells of living species, indicating an ancient coast-line.
Glacial Formations of North America.—In the western hemisphere,
both in Canada and as far south as the 40th and even 38th parallel of

latitude in the United States, we meet with a repetition of all the
peculiarities which distinguish the European boulder formation. Fragments
of rock have travelled for great distances, especially from north to south:
the surface of the subjacent rock is smoothed, striated, and fluted;
unstratified mud or till containing boulders is associated with strata of loam,
sand, and clay, usually devoid of fossils. Where shells are present, they are
of species still living in northern seas, and not a few of them identical with
those belonging to European drift, including most of those already given in
Figs. 107 to 112, p. 176. The fauna also of the glacial epoch in North
America is less rich in species than that now inhabiting the adjacent sea,
whether in the Gulf of St. Lawrence, or off the shores of Maine, or in the
Bay of Massachusetts.
The extension on the American continent of the range of erratics during
the Post-pliocene period to lower latitudes than they reached in Europe,
agrees well with the present southward deflection of the isothermal lines, or
rather the lines of equal winter temperature. It seems that formerly, as now,
a more extreme climate and a more abundant supply of ice prevailed on the
western side of the Atlantic. Another resemblance between the distribution
of the drift fossils in Europe and North America has yet to be pointed out.
In Canada and the United States, as in Europe, the marine shells are
generally confined to very moderate elevations above the sea (between 100
and 700 feet), while the erratic blocks and the grooved and polished
surfaces of rock extend to elevations of several thousand feet.
I have already mentioned that in Europe several quadrupeds of living, as
well as extinct, species were common to pre-glacial and post-glacial times.
In like manner there is reason to suppose that in North America much of the
ancient mammalian fauna, together with nearly all the invertebrata, lived
through the ages of intense cold. That in the United States the Mastodon
giganteus was very abundant after the drift period, is evident from the fact
that entire skeletons of this animal are met with in bogs and lacustrine
deposits occupying hollows in the glacial drift. They sometimes occur in the
bottom even of small ponds recently drained by the agriculturist for the
sake of the shell-marl. In 1845 no less than six skeletons of the same
species of Mastodon were found in Warren county, New Jersey, six feet
below the surface, by a farmer who was digging out the rich mud from a
small pond which he had drained. Five of these skeletons were lying

together, and a large part of the bones crumbled to pieces as soon as they
were exposed to the air.
It would be rash, however, to infer from such data that these quadrupeds
were mired in modern times, unless we use that term strictly in a geological
sense. I have shown that there is a fluviatile deposit in the valley of the
Niagara, containing shells of the genera Melania, Lymnea, Planorbis,
Velvata, Cyclaz, Unio, Helix, etc., all of recent species, from which the
bones of the great Mastodon have been taken in a very perfect state. Yet the
whole excavation of the ravine, for many miles below the Falls, has been
slowly effected since that fluviatile deposit was thrown down. Other extinct
animals accompany the Mastodon giganteus in the post-glacial deposits of
the United States, and this, taken with the fact that so few of the mollusca,
even of the commencement of the cold period, differ from species now
living is important, as refuting the hypothesis, for which some have
contended, that the intensity of the glacial cold annihilated all the species in
temperate and arctic latitudes.
Connection of the Predominance of Lakes with Glacial Action.—It
was first pointed out by Professor Ramsay in 1862, that lakes are
exceedingly numerous in those countries where erratics, striated blocks, and
other signs of ice-action abound; and that they are comparatively rare in
tropical and sub-tropical regions. Generally in countries where the winter
cold is intense, such as Canada, Scandinavia, and Finland, even the plains
and lowlands are thickly strewn with innumerable ponds and small lakes,
together with some others of a larger size; while in more temperate regions,
such as Great Britain, Central and Southern Europe, the United States, and
New Zealand, lake districts occur in all such mountainous tracts as can be
proved to have been glaciated in times comparatively modern or since the
geographical configuration of the surface bore a considerable resemblance
to that now prevailing. In the same countries, beyond the glaciated regions,
lakes abruptly cease, and in warmer and tropical countries are either
entirely absent, or consist, as in equatorial Africa, of large sheets of water
unaccompanied so far as we yet know by numerous smaller ponds and
tarns.
The southern limits of the lake districts of the Northern Hemisphere are
found at about 40° N. latitude on the American continent, and about 50° in
Europe, or where the Alps intervene four degrees farther south. A large

proportion of the smaller lakes are dammed up by barriers of unstratified
drift, having the exact character of the moraines of glaciers, and are termed
by geologists “morainic,” but some of them are true rock-basins, and would
hold water even if all the loose drift now resting on their margins were
removed.
In a paper read before the Geological Society of London in 1862,
Professor Ramsay maintained that the first formation of most existing lakes
took place during the glacial epoch, and was due, not to elevation or
subsidence, but to actual erosion of their basins by glaciers. M. Mortillet in
the same year advanced the theory that after the Alpine lake-basins had
been filled up with loose fluviatile deposits, they were re-excavated by the
great glaciers which passed down the valleys at the time of the greatest
cold, a doctrine which would attribute to moving ice almost as great a
capacity of erosion as that which assumed that the original basins were
scooped out of solid rock by glaciers. It is impossible to deny that the mere
geographical distribution of lakes points to the intimate connection of their
origin with the abundance of ice during a former excess of cold, but how far
the erosive action of moving ice has been the sole or even the principal
cause of lake-basins, is a question still open to discussion.
The lakes of Switzerland and the north of Italy are some of them twenty
and thirty miles in length, and so deep that their bottoms are in some cases
from 1000 to 2000 feet beneath the level of the sea. It is admitted on all
hands that they were once filled with ice, and as the existing glaciers polish
and grind down, as before stated, the surface of the rocks, we are prepared
to find that every lake-basin in countries once covered by ice should bear
the marks of superficial glaciation, and also that the ice during its advance
and retreat should have left behind it much transported matter as well as
some evidence of its having enlarged the pre-existing cavity. But much
more than this is demanded by the advocates of glacial erosion. They
suggest that as the old extinct glaciers were several thousand feet thick, they
were able in some places gradually to scoop out of the solid rock cavities
twenty or thirty miles in length, and as in the case of Lago Maggiore from a
thousand to two thousand six hundred feet below the previous level of the
river-channel, and also that the ice had the power to remove from the cavity
formed by its grinding action all the materials of the missing rocks. A
constant supply, it is argued, of fine mud issues from the termination of
every glacier in the stream which is produced by the melting of the ice, and

this result of friction is exhibited both during winter and summer, affording
evidence of the continual deepening and widening of the valleys through
which glaciers pass. As the fine mud is carried away by a river from the
deep pool which is formed from the base of every cataract, so it seems to be
imagined that lake-basins may be gradually emptied of the mud formed by
abrasion during the glacial period.
I am by no means disposed to object to this theory on the ground of the
insufficiency of the time during which the extreme cold endured, but we
must carefully consider whether that same time is not so vast as to make it
probable that other forces, besides the motion of glaciers, must have
cooperated in converting some parts of the ancient valley courses into lake-
basins. They who have formed the most exalted conceptions of the erosive
energy of moving ice do not deny that during the period termed “Glacial”
there have been movements of the earth’s crust sufficient to produce
oscillations of level in Europe amounting to 1000 feet or more in both
directions. M. Charpentier, indeed, attributed some of the principal changes
of climate in Switzerland, during the glacial period, to a depression of the
central Alps to the extent of 3000 feet, and Swiss geologists have long been
accustomed to attribute their lake basins, in part, to those convulsions by
which the shape and course of the valleys may have been modified. Our
experience, in the lifetime of the present generation, of the changes of level
witnessed in New Zealand during great earthquakes is entirely opposed to
the notion that the movements, whether upward or downward, are uniform
in amount or direction throughout areas of indefinite extent. On the
contrary, the land has been permanently raised in one region several feet or
yards, and the rise has been found gradually to die out, so as to be
imperceptible at a distance of twenty miles, and in some areas is even
exchanged for a simultaneous downward movement of several feet.
But, it is asked, if such inequality of movement can have contributed
towards the production of lake basins, does it not leave unexplained the
comparative rarity of lakes in tropical and subtropical countries. In reply to
this question it may be observed that in our endeavour to estimate the
effects of subterranean movements in modifying the superficial geography
of a country we must remember that each convulsion effects a very slight
change. If it interferes with the drainage, whether by raising the lower or
sinking the higher portion of a hydrographical basin, the upheaval or
depression will only amount to a few feet at a time, and there may be an

interval of years or centuries before any further movement takes place in
the same region. In the mean time an incipient lake if produced may be
filled up with sediment, and the recently-formed barrier will then be cut
through by the river, whereas in a country where glacial conditions prevail
no such obliteration of the temporary lake-basin would take place; for
however deep it became by repeated sinking of the upper or rising of the
lower extremity, being always filled with ice it might remain, throughout
the greater part of its extent, free from sediment or drift until the ice melted
at the close of the glacial period.
One of the most serious objections to the exclusive origin by ice-erosion
of wide and deep lake-basins arises from their capricious distribution, as for
example in Piedmont, both to the eastward and westward of Turin, where
great lakes are wanting,[6] although some of the largest extinct glaciers
descending from Mont Blanc and Monte Rosa came down from the Alps,
leaving their gigantic moraines in the low country. Here, therefore, we
might have expected to find lakes of the first magnitude rivalling the
contiguous Lago Maggiore in importance.
A still more striking illustration of the same absence of lakes where large
glaciers abound is afforded by the Caucasus, a chain more than 300 miles
long, and the loftiest peaks of which attain heights from 16,000 to 18,000
feet. This greatest altitude is reached by Elbruz, a mountain in lat. 43° N.
three degrees south of Mont Blanc, but on the other hand 3000 feet higher.
The present Caucasian glaciers are equal or superior in dimensions to those
of Switzerland, and like them give rise occasionally to temporary lakes by
obstructing the course of rivers, and causing great floods when the icy
barriers give way. Mr. Freshfield, a careful observer, writing in 1869, says:
[7]
“A total absence of lakes on both sides of the chains is the most marked
feature. Not only are there no great subalpine sheets of water, like Como or
Geneva, but mountain tarns, such as the Dauben See on the Gemmi, or the
Klonthal See near Glarus, are equally wanting.” The same author states on
the authority of the eminent Swiss geologist, Mons. E. Favre, who also
explored the Caucasus in 1868, that moraines of great height and huge
erratics of granite and other rocks “justify the assertion that the present
glaciers of the Caucasus, like those of the Alps, are only the shadows of
their former selves.”

It seems safe to assume that the chain of lakes, of which the Albert
Nyanza forms one in equatorial Africa, was due to causes other than glacial.
Yet if we could imagine a glacial period to visit that region filling the lakes
with ice and scoring the rocks which form their sides and bottoms, we
should be unable to decide how much the capacity of the basins had been
enlarged and the surface modified by glacial erosion. The same may be true
of the Lago Maggiore and Lake Superior, although the present basins of
both of them afford abundant superficial markings due to ice-action.
But to whatever combination of causes we attribute the great Alpine lakes
one thing is clear, namely, that they are, geologically speaking, of modern
origin. Every one must admit that the upper valley of the Rhone has been
chiefly caused by fluviatile denudation, and it is obvious that the quantity of
matter removed from that valley previous to the glacial period would have
been amply sufficient to fill up with sediment the basin of the Lake of
Geneva, supposing it to have been in existence, even if its capacity had
been many times greater than it is now.[8]
On the whole, it appears to me, in accordance with the views of Professor
Ramsay, M. Mortillet, Mr. Geikie, and others, that the abrading action of ice
has formed some mountain tarns and many morainic lakes; but when it is a
question of the origin of larger and deeper lakes, like those of Switzerland
or the north of Italy, or inland fresh-water seas, like those of Canada, it will
probably be found that ice has played a subordinate part in comparison with
those movements by which changes of level in the earth’s crust are
gradually brought about.
[1] Jamieson, Quart. Geol. Journ., 1860, vol. xvi, p. 370.

[2] Bryce, Quart. Geol. Journ., vol. xxi, p. 217, 1865.

[3] Geikie, Trans. Geol. Soc. Glasgow, vol. i, part ii, p. 68, 1863.

[4] Milne Home, Trans. Royal Soc. Edinburgh, vol. xxv, 1868-9.

[5] Quart. Geol. Journ., 1852, vol. viii, p. 372.

[6] Antiquity of Man, p. 313.

[7] Travels in Central Caucasus, 1869, p. 452.

[8] See Principles, vol. i, p. 420, 10th ed., 1867.

TERTIARY OR CAINOZOIC PERIOD

CHAPTER XIII.
PLIOCENE PERIOD

Glacial Formations of Pliocene Age. — Bridlington Beds.
— Glacial Drifts of Ireland. — Drift of Norfolk Cliffs. —
Cromer Forest-bed. — Aldeby and Chillesford Beds. —
Norwich Crag. — Older Pliocene Strata. — Red Crag of
Suffolk. — Coprolitic Bed of Red Crag. — White or
Coralline Crag. — Relative Age, Origin, and Climate of the
Crag Deposits. — Antwerp Crag. — Newer Pliocene Strata
of Sicily. — Newer Pliocene Strata of the Upper Val d’Arno.
— Older Pliocene of Italy. — Subapennine Strata. — Older
Pliocene Flora of Italy.

It will be seen in the description given in the last chapter of the Post-
pliocene formations of the British Isles that they comprise a large
proportion of those commonly termed glacial, characterised by shells
which, although referable to living species, usually indicate a colder climate
than that now belonging to the latitudes where they occur fossil. But in
parts of England, more especially in Yorkshire, Norfolk, and Suffolk, there
are superficial formations of clay with glaciated boulders, and of sand and
pebbles, containing occasional, though rare, patches of shells, in which the
marine fauna begins to depart from that now inhabiting the neighbouring
sea, and comprises some species of mollusca not yet known as living, as
well as extinct varieties of others, entitling us to class them as Newer
Pliocene, although belonging to the close of that period and chronologically
on the verge of the later or Post-pliocene epoch.
Bridlington Drift.—To this era belongs the well-known locality of
Bridlington, near the mouth of the Humber, in Yorkshire, where about
seventy species or well-marked varieties of shells have been found on the
coast, near the sea-level, in a bed of sand several feet thick resting on

glacial clay with much chalk débris, and covered by a deposit of purple clay
with glaciated boulders. More than a third of the species in this drift are
now inhabitants of arctic regions, none of them extending southward to the
British seas; which is the more remarkable as Bridlington is situated in lat.
54° north. Fifteen species are British and Arctic, a very few belong to those
species which range south of our British seas. Five species or well-marked
varieties are not known living, namely, the variety of Astarte borealis
(called A. Withami); A. mutabilis; the sinistral form of Tritonium carinatum,
Cardita analis, and Tellina obliqua, Fig. 120, p. 194. Mr. Searles Wood also
inclines to consider Nucula Cobboldiæ, Fig. 119, p. 194, now absent from
the European seas and the Atlantic, as specifically distinct from a closely-
allied shell now living in the seas surrounding Vancouver’s Island, which
some conchologists regard as a variety. Tellina obliqua also approaches
very near to a shell now living in Japan.
Glacial Drift of Ireland.—Marine drift containing the last-mentioned
Nucula and other glacial shells reaches a height of from 1000 to 1200 feet
in the county of Wexford, south of Dublin. More than eighty species have
already been obtained from this formation, of which two, Conovulus
pyramidalis and Nassa monensis, are not known as living; while Turritella
incrassata and Cypræa lucida no longer inhabit the British seas, but occur
in the Mediterranean. The great elevation of these shells, and the still
greater height to which the surface of the rocks in the mountainous regions
of Ireland have been smoothed and striated by ice-action, has led geologists
to the opinion that that island, like the greater part of England and Scotland,
after having been united with the continent of Europe, from whence it
received the plants and animals now inhabiting it, was in great part
submerged. The conversion of this and other parts of Great Britain into an
archipelago was followed by a re-elevation of land and a second continental
period. After all these changes the final separation of Ireland from Great
Britain took place, and this event has been supposed to have preceded the
opening of the straits of Dover.[1]

Drift of Norfolk Cliffs.—There are deposits of boulder clay and till in
the Norfolk cliffs principally made up of the waste of white chalk and flints
which, in the opinion of Mr. Searles Wood, jun., and others, are older than
the Bridlington drift, and contain a larger proportion of shells common to
the Norwich and Red Crag, including a certain number of extinct forms, but
also abounding in Tellina balthica (T. solidula, Fig. 116), which is found
fossil at Bridlington, and living in our British seas, but wanting in all the
formations, even the newest, afterwards to be described as Crag. As the
greater part of these drifts are barren of organic remains, their classification
is at present a matter of great uncertainty.
They can nowhere be so advantageously studied as on the coast between
Happisburgh and Cromer. Here we may see vertical cliffs, sometimes 300
feet and more in height, exposed for a distance of fifty miles, at the base of
which the chalk with flints crops out in nearly horizontal strata. Beds of
gravel and sand repose on this undisturbed chalk. They are often strangely
contorted, and envelop huge masses or erratics of chalk with layers of
vertical flint. I measured one of these fragments in 1839 at Sherringham,
and found it to be eighty feet in its longest diameter. It has been since
entirely removed by the waves of the sea. In the floor of the chalk beneath it
the layers of flint were horizontal. Such erratics have evidently been moved
bodily from their original site, probably by the same glacial action which
has polished and striated some of the accompanying granitic and other
boulders, occasionally six feet in diameter, which are imbedded in the drift.
Cromer Forest-bed.—Intervening between these glacial formations and
the subjacent chalk lies what has been called the Cromer Forest-bed. This
buried forest has been traced from Cromer to near Kessingland, a distance
of more than forty miles, being exposed at certain seasons between high and
low water mark. It is the remains of an old land and estuarine deposit,
containing the submerged stumps of trees standing erect with their roots in
the ancient soil. Associated with the stumps and overlying them, are lignite
beds with fresh-water shells of recent species, and laminated clay without
fossils. Through the lignite and forest-bed are scattered cones of the Scotch
and spruce firs with the seeds of recent plants, and the bones of at least
twenty species of terrestrial mammalia. Among these are two species of
elephant, E. meridionalis, Nesti, and E. antiquus, the former found in the
Newer Pliocene beds of the Val d’Arno, near Florence. In the same bed
occur Hippopotamus major, Rhinoceros etruscus, both of them also Val

d’Arno species, many species of deer considered by Mr. Boyd Dawkins to
be characteristic of warmer countries, and also a horse, beaver, and field-
mouse. Half of these mammalia are extinct, and the rest still survive in
Europe. The vegetation taken alone does not imply a temperature higher
than that now prevailing in the British Isles. There must have been a
subsidence of the forest to the amount of 400 or 500 feet, and a re-elevation
of the same to an equal extent in order to allow the ancient surface of the
chalk or covering of soil, on which the forest grew, to be first covered with
several hundred feet of drift, and then upheaved so that the trees should
reach their present level. Although the relative antiquity of the forest-bed to
the overlying glacial till is clear, there is some difference of opinion as to its
relation to the crag presently to be described.

Chillesford and Aldeby Beds.—It is in the counties of Norfolk, Suffolk,
and Essex, that we obtain our most valuable information respecting the
British Pliocene strata, whether newer or older. They have obtained in those
counties the provincial name of “Crag,” applied particularly to masses of
shelly sand which have long been used in agriculture to fertilise soils
deficient in calcareous matter. At Chillesford, between Woodbridge and
Aldborough in Suffolk, and Aldeby, near Beccles, in the same county, there
occur stratified deposits, apparently older than any of the preceding drifts of
Yorkshire, Norfolk, and Suffolk. They are composed at Chillesford of
yellow sands and clays, with much mica, forming horizontal beds about
twenty feet thick. Messrs. Prestwich and Searles Wood, senior, who first
described these beds, point out that the shells indicate on the whole a colder
climate than the Red Crag; two-thirds of them being characteristic of high
latitudes. Among these are Cardium Grœnlandicum, Leda limatula,
Tritonium carinatum, and Scalaria Grœnlandica. In the upper part of the
laminated clays a skeleton of a whale was found associated with casts of the
characteristic shells, Nucula Cobboldiæ and Tellina obliqua, already
referred to as no longer inhabiting our seas, and as being extinct varieties if
not species. The same shells occur in a perfect state in the lower part of the

formation. Natica helicoides (Fig. 117) is an example of a species formerly
known only as fossil, but which has now been found living in our seas.
At Aldeby, where beds occur decidedly similar in mineral character as
well as fossil remains, Messrs. Crowfoot and Dowson have now obtained
sixty-six species of mollusca, comprising the Chillesford species and some
others. Of these about nine-tenths are recent. They are in a perfect state,
clearly indicating a cold climate; as two-thirds of them are now met with in
arctic regions. As a rule, the lamellibranchiate molluscs have both valves
united, and many of them, such as Mya arenaria, stand with the siphonal
end upward, as when in a living state. Tellina balthica, before mentioned
(Fig. 116) as so characteristic of the glacial beds, including the drift of
Bridlington, has not yet been found in deposits of Chillesford and Aldeby
age, whether at Sudbourn, East Bavent, Horstead, Coltishall, Burgh, or in
the highest beds overlying the Norwich Crag proper at Bramerton and
Thorpe.

Norwich or Fluvio-marine Crag.—The beds above alluded to ought,
perhaps, to be regarded as beds of passage between the glacial formations
and those called from a provincial name “Crag,” the newest member of
which has been commonly called the “Norwich Crag.” It is chiefly seen in
the neighbourhood of Norwich, and consists of beds of incoherent sand,
loam, and gravel, which are exposed to view on both banks of the Yare, as
at Bramerton and Thorpe. As they contain a mixture of marine, land, and
fresh-water shells, with bones of fish and mammalia, it is clear that these
beds have been accumulated at the bottom of a sea near the mouth of a
river. They form patches rarely exceeding twenty feet in thickness, resting

on white chalk. At their junction with the chalk there invariably intervenes a
bed called the “Stone-bed,” composed of unrolled chalk-flints, commonly
of large size, mingled with the remains of a land fauna comprising
Mastodon arvernensis, Elephas meridionalis, and an extinct species of deer.
The mastodon, which is a species characteristic of the Pliocene strata of
Italy and France, is the most abundant fossil, and one not found in the
Cromer forest before mentioned. When these flints, probably long exposed
in the atmosphere, became submerged, they were covered with barnacles,
and the surface of the chalk became perforated by the Pholas crispata, each
fossil shell still remaining at the bottom of its cylindrical cavity, now filled
up with loose sand from the incumbent crag. This species of Pholas still
exists, and drills the rocks between high and low water on the British coast.
The name of “Fluvio-marine” has often been given to this formation, as no
less than twenty species of land and fresh-water shells have been found in
it. They are all of living species; at least only one univalve, Paludina lenta,
has any, and that a very doubtful, claim to be regarded as extinct.

Of the marine shells, 124 in number, about 18 per cent are extinct,
according to the latest estimate given me by Mr. Searles Wood; but, for
reasons presently to be mentioned, this percentage must be only regarded as
provisional. It must also be borne in mind that the proportion of recent
shells would be augmented if the uppermost beds at Bramerton, near
Norwich, which belong to the most modern or Chillesford division of the
Crag, had been included, as they were formerly, by Mr. Woodward and
myself, in the Norwich series. Arctic shells, which formed so large a
proportion in the Chillesford and Aldeby beds, are more rare in the Norwich
Crag, though many northern species—such as Rhynchonella psittacea,
Scalaria Grœnlandica, Astarte borealis, Panopæa Norvegia, and others—
still occur. The Nucula Cobboldiæ and Tellina obliqua, Figs. 119 and 120,
before mentioned, p. 194, are frequent in these beds, as are also Littorina
littorea, Cardium edule, and Turritella communis, of our seas, proving the
littoral origin of the beds.

OLDER PLIOCENE STRATA.

Red Crag.—Among the English Pliocene beds the next in antiquity is
the Red Crag, which often rests immediately on the London Clay, as in the
county of Essex, illustrated in Fig. 121.

It is chiefly in the county of Suffolk that it is found, rarely exceeding
twenty feet in thickness, and sometimes overlying another Pliocene deposit,
the Coralline Crag, to be mentioned in the sequel. It has yielded—exclusive
of 25 species regarded by Mr. Wood as derivative—256 species of
mollusca, of which 65, or 25 per cent, are extinct. Thus, apart from its order
of superposition, its greater antiquity than the Norwich and glacial beds,
already described, is proved by the greater departure from the fauna of our
seas. It may also be observed that in most of the deposits of this Red Crag,
the northern forms of the Norwich Crag, and of such glacial formations as
Bridlington, are less numerous, while those having a more southern aspect
begin to make their appearance. Both the quartzose sand, of which it chiefly
consists, and the included shells, are most commonly distinguished by a
deep ferruginous or ochreous colour, whence its name. The shells are often
rolled, sometimes comminuted, and the beds have much the appearance of
having been shifting sand-banks, like those now forming on the Dogger-
bank, in the sea, sixty miles east of the coast of Northumberland. Cross
stratification is almost always present, the planes of the strata being
sometimes directed towards one point of the compass, sometimes to the
opposite, in beds immediately overlying. That such a structure is not
deceptive or due to any subsequent concretionary rearrangement of
particles, or to mere bands of colour produced by the iron, is proved by
each bed being made up of flat pieces of shell which lie parallel to the
planes of the smaller strata.
It has long been suspected that the different patches of Red Crag are not
all of the same age, although their chronological relation cannot be decided
by superposition. Separate masses are characterised by shells specifically
distinct or greatly varying in relative abundance, in a manner implying that
the deposits containing them were separated by intervals of time. At Butley,

Tunstall, Sudbourn, and in the Red Crag of Chillesford, the mollusca appear
to assume their most modern aspect when the climate was colder than when
the earliest deposits of the same period were formed. At Butley, Nucula
Cobboldiæ, so common in the Norwich and certain glacial beds, is found,
and Purpura tetragona (Fig. 122) is very abundant. On the other hand, at
Walton-on-the-Naze, in Essex, we seem to have an exhibition of the oldest
phase of the Red Crag; and a warmer climate seems indicated, not only by
the absence of many northern forms, but also by the abundance of some
now living in the British seas and the Mediterranean. Voluta Lamberti (see
Figs. 123 and 124), an extinct form, which seems to have flourished chiefly
in the antecedent Coralline Crag period, is still represented here by
individuals of every age.

The reversed whelk (Fig. 125) is common at Walton, where the dextral
form of that shell is unknown. Here also we find most frequently specimens
of lamellibranchiate molluscs, with both the valves united, showing that
they belonged to this sea of the Upper Crag, and were not washed in from
an older bed, such as the Coralline, in which case the ligament would not
have held together the valves in strata so often showing signs of the
boisterous action of the waves. No less than forty species of
lamellibranchiate molluscs, with double valves, have been collected by Mr.
Bell from the various localities of the Red Crag.

At and near the base of the Red Crag is a loose bed of brown nodules,
first noticed by Professor Henslow as containing a large percentage of
earthy phosphates. This bed of coprolites (as it is called, because they were
originally supposed to be the fæces of animals) does not always occur at
one level, but is generally in largest quantity at the junction of the Crag and
the underlying formation. In thickness it usually varies from six to eighteen
inches, and in some rare cases amounts to many feet. It has been much used
in agriculture for manure, as not only the nodules, but many of the separate
bones associated with them, are largely impregnated with phosphate of
lime, of which there is sometimes as much as sixty per cent. They are not
unfrequently covered with barnacles, showing that they were not formed as
concretions in the stratum where they now lie buried, but had been
previously consolidated. The phosphatic nodules often collect fossil crabs
and fishes from the London Clay, together with the teeth of gigantic sharks.
In the same bed have been found many ear-bones of whales, and the teeth
of Mastodon arvernensis, Rhinoceros Schleiermacheri, Tapirus priscus, and
Hipparion (a quadruped of the horse family), and antlers of a stag, Cervus
anoceros. Organic remains also of the older chalk and Lias are met with,
showing how great was the denudation of previous formations during the
Pliocene period. As the older White Crag, presently to be mentioned,
contains similar phosphatic nodules near its base, those of the Red Crag
may be partly derived from this source.

White or Coralline Crag.—The lower or Coralline Crag is of very
limited extent, ranging over an area about twenty miles in length, and three
or four in breadth, between the rivers Stour and Alde, in Suffolk. It is
generally calcareous and marly—often a mass of comminuted shells, and
the remains of bryozoa[2] (or polyzoa), passing occasionally into a soft
building-stone. At Sudbourn and Gedgrave, near Orford, this building-stone
has been largely quarried. At some places in the neighbourhood the softer
mass is divided by thin flags of hard limestone, and bryozoa placed in the
upright position in which they grew. From the abundance of these coralloid
mollusca the lowest or White Crag obtained its popular name, but true
corals, as now defined, or zoantharia, are very rare in this formation.
The Coralline Crag rarely, if ever, attains a thickness of thirty feet in any
one section. Mr. Prestwich imagines that if the beds found at different
localities were united in the probable order of their succession, they might
exceed eighty feet in thickness, but Mr. Searles Wood does not believe in
the possibility of establishing such a chronological succession by aid of the
organic remains, and questions whether proof could be obtained of more
than forty feet. I was unable to come to any satisfactory opinion on the
subject, although at Orford, especially at Gedgrave, in the neighbourhood of
that place, I saw many sections in pits, where this crag is cut through. These
pits are so unconnected, and of such limited extent, that no continuous
section of any length can be obtained, so that speculations as to the
thickness of the whole deposit must be very vague. At the base of the
formation at Sutton a bed of phosphatic nodules, very similar to that before
alluded to in the Red Crag, with remains of mammalia, has been met with.

Whenever the Red and Coralline Crag occur in the same district, the Red
Crag lies uppermost; and in some cases, as in the section represented in Fig.
126, which I had an opportunity of seeing exposed to view in 1839, it is
clear that the older deposit, or Coralline Crag, b, had suffered denudation,
before the newer formation, a, was thrown down upon it. At D there was
not only seen a distinct cliff, eight or ten feet high, of Coralline Crag,
running in a direction N.E. and S.W., against which the Red Crag abuts with

its horizontal layers, but this cliff occasionally overhangs. The rock
composing it is drilled everywhere by Pholades, the holes which they
perforated having been afterwards filled with sand, and covered over when
the newer beds were thrown down. The older formation is shown by its
fossils to have accumulated in a deeper sea, and contains none of those
littoral forms such as the limpet, Patella, found in the Red Crag. So great an
amount of denudation could scarcely take place, in such incoherent
materials, without some of the fossils of the inferior beds becoming mixed
up with the overlying crag, so that considerable difficulty must be
occasionally experienced by the palæontologist in deciding which species
belong severally to each group.

Mr. Searles Wood estimates the total number of marine testaceous
mollusca of the Coralline Crag at 350, of which 110 are not known as
living, being in the proportion of thirty-one per cent extinct. No less than
130 species of bryozoa have been found in the Coralline Crag, and some
belong to genera unknown in the living creation, and of a very peculiar
structure; as, for example, that represented in Fig. 127, which is one of

several species having a globular form. Among the testacea the genus
Astarte (see Fig. 128) is largely represented, no less than fourteen species
being known, and many of these being rich in individuals. There is an
absence of genera peculiar to hot climates, such as Conus, Oliva,
Fasciolaria, Crassatella, and others. The absence also of large cowries
(Cyprea), those found belonging exclusively to the section Trivia, is
remarkable. The large volute, called Voluta Lamberti (Fig. 123, p. 196),
may seem an exception; but it differs in form from the volutes of the torrid
zone, and, like the living Voluta Magellanica, must have been fitted for an
extra-tropical climate.

The occurrence of a species of Lingula at Sutton (see Fig. 129) is worthy
of remark, as these Brachiopoda seem now confined to more equatorial
latitudes; and the same may be said still more decidedly of a species of
Pyrula, supposed by Mr. Wood to be identical with P. reticulata (Fig. 130),
now living in the Indian Ocean. A genus also of echinoderms, called by
Professor Forbes Temnechinus (Fig. 131), occurs in the Red and Coralline
Crag of Suffolk, and until lately was unknown in a living state, but it has
been brought to light as an existing form by the deep-sea dredgings, both of
the United States survey, off Florida, at a depth of from 180 to 480 feet, and
more recently (1869), in the British seas, during the explorations of the
“Porcupine.”
Climate of the Crag Deposits.—One of the most interesting conclusions
deduced from a careful comparison of the shells of the British Pliocene
strata and the fauna of our present seas has been pointed out by Professor E.
Forbes. It appears that, during the Glacial period, a period intermediate, as
we have seen, between that of the Crag and our own time, many shells,
previously established in the temperate zone, retreated southward to avoid
an uncongenial climate, and they have been found fossil in the Newer

Pliocene strata of Sicily, Southern Italy, and the Grecian Archipelago, where
they may have enjoyed, during the era of floating icebergs, a climate
resembling that now prevailing in higher European latitudes.[3] The
Professor gave a list of fifty shells which inhabited the British seas while
the Coralline and Red Crag were forming, and which, though now living in
our seas, were wanting, as far as was then known, in the glacial deposits.
Some few of these species have subsequently been found in the glacial drift,
but the general conclusion of Forbes remains unshaken.
The transport of blocks by ice, when the Red Crag was being deposited,
appears to me evident from the large size of some huge, irregular, quite
unrounded chalk flints, retaining their white coating, and 2 feet long by 18
inches broad, in beds worked for phosphatic nodules at Foxhall, four miles
south-east of Ipswich. These must have been tranquilly drifted to the spot
by floating ice. Mr. Prestwich also mentions the occurrence of a large block
of porphyry in the base of the Coralline Crag at Sutton, which would imply
that the ice-action had begun in our seas even in this older period. The cold
seems to have gone on increasing from the time of the Coralline to that of
the Norwich Crag, and became more and more severe, not perhaps without
some oscillations of temperature, until it reached its maximum in what has
been called the Glacial period, or at the close of the Newer Pliocene, and in
the Post-pliocene periods.
Relation of the Fauna of the Crag to that of the recent Seas.—By far
the greater number of the recent marine species occurring in the several
Crag formations are still inhabitants of the British seas; but even these differ
considerably in their relative abundance, some of the commonest of the
Crag shells being now extremely scarce—as, for example, Buccinum Dalei
—while others, rarely met with in a fossil state, are now very common, as
Murex erinaceus and Cardium echinatum. Some of the species also, the
identity of which with the living would not be disputed by any
conchologist, are nevertheless distinguishable as varieties, whether by slight
deviations in form or a difference in average dimensions. Since Mr. Searles
Wood first described the marine testacea of the Crags, the additions made to
that fossil fauna have not been considerable, whereas we have made in the
same period immense progress in our knowledge of the living testacea of
the British and arctic seas, and of the Mediterranean. By this means the
naturalist has been enabled to identify with existing species many forms
previously supposed to be extinct.

In the forthcoming supplement to the invaluable monograph
communicated by Mr. Wood to the Palæontographical Society, in which he
has completed his figures and descriptions of the British crag shells of
every age, list will be found of all the fossil shells, of which a summary is
given in the table, p. 202.
To begin with the uppermost or Chillesford beds, it will be seen that
about 9 per cent only are extinct, or not known as living, whereas in the
Norwich, which succeeds in the descending order, seventeen in a hundred
are extinct. Formerly, when the Norwich or Fluvio-marine Crag was spoken
of, both these formations were included under the same head, for both at
Bramerton and Thorpe, the chief localities where the Norwich Crag was
studied, an overlying deposit occurs referable to the Chillesford age. If now
the two were fused together as of old, their shells would, according to Mr.
Wood, yield a percentage of fifteen in a hundred of species extinct or not
known as living.

NUMBER OF KNOWN SPECIES OF MARINE TESTACEA IN THE
CRAG.

CHILLESFORD AND ALDEBY BEDS
Percentage of
Not Shells not
Total known known
number as living as living
Bivalves 61 4
Univalves 33 5 9·5
Brachiopods 0 0
NORWICH OR FLUVIO-MARINE CRAG
Bivalves 61 10
Univalves 64 12 17·5
Brachiopods 1 0
RED CRAG
(Exclusive to many derivative shells)
Bivalves 128 31
Univalves 127 33 25·0
Brachiopods 1 1

CORALLINE CRAG
Bivalves 161 47
Univalves 184 60 31·5
Brachiopods 5 3
To come next to the Red Crag, the reader will observe that a percentage
of 25 is given of shells unknown as living, and this increases to 31 in the
antecedent Coralline Crag. But the gap between these two stages of our
Pliocene deposits is really wider than these numbers would indicate, for
several reasons. In the first place, the Coralline Crag is more strictly the
product of a single period, the Red Crag, as we have seen, consisting of
separate and independent patches, slightly varying in age, of which the
newest is probably not much anterior to the Norwich Crag. Secondly, there
was a great change of conditions, both as to the depth of the sea and
climate, between the periods of the Coralline and Red Crag, causing the
fauna in each to differ far more widely than would appear from the above
numerical results.
The value of the analysis given in the above table of the shells of the Red
and Coralline Crags is in no small degree enhanced by the fact that they
were all either collected by Mr. Wood himself, or obtained by him direct
from their discoverers, so that he was enabled in each case to test their
authenticity, and as far as possible to avoid those errors which arise from
confounding together shells belonging to the sea of a newer deposit, and
those washed into it from a formation of older date. The danger of this
confusion may be conceived when we remember that the number of species
rejected from the Red Crag as derivative by Mr. Wood is no less than 25.
Some geologists have held that on the same grounds it is necessary to
exclude as spurious some of the species found in the Norwich Crag proper;
but Mr. Wood does not entertain this view, believing that the spurious shells
which have sometimes found their way into the lists of this crag have been
introduced by want of care from strata of Red Crag.
There can be no doubt, on the other hand, that conchologists have
occasionally rejected from the Red and Norwich Crags, as derivative, shells
which really belonged to the seas of those periods, because they were
extinct or unknown as living, which in their eyes afforded sufficient ground
for suspecting them to be intruders. The derivative origin of a species may
sometimes be indicated by the extreme scarcity of the individuals, their

colour, and worn condition; whereas an opposite conclusion may be arrived
at by the integrity of the shells, especially when they are of delicate and
tender structure, or their abundance, and, in the case of the
lamellibranchiata, by their being held together by the ligament, which often
happens when the shells have been so broken that little more than the
hinges of the two valves are preserved. As to the univalves, I have seen
from a pit of Red Crag, near Woodbridge, a large individual of the extinct
Voluta Lamberti, seven inches in length, of which the lip, then perfect, had
in former stages of its growth been frequently broken, and as often repaired.
It had evidently lived in the sea of the Red Crag, where it had been exposed
to rough usage, and sustained injuries like those which the reversed whelk,
Trophon antiquum, so characteristic of the same formation, often exhibits.
Additional proofs, however, have lately been obtained by Mr. Searles Wood
that this shell had not died out in the era of the Red Crag by the discovery
of the same fossil near Southwold, in beds of the later Norwich Crag.
Antwerp Crag.—Strata of the same age as the Red and Coralline Crag
of Suffolk have been long known in the country round Antwerp, and on the
banks of the Scheldt, below that city; and the lowest division, or Black
Crag, there found, is shown by the shells to be somewhat more ancient than
any of our British series, and probably forms the first links of a downward
passage from the strata of the Pliocene to those of the Upper Miocene
period.

Newer Pliocene Strata of Sicily.—At several points north of Catania, on
the eastern sea-coast of Sicily—as at Aci-Castello, for example, Trezza, and
Nizzeti—marine strata, associated with volcanic tuffs and basaltic lavas, are
seen, which belong to a period when the first igneous eruptions of Mount
Etna were taking place in a shallow bay of the Mediterranean. They contain

numerous fossil shells, and out of 142 species that have been collected all
but eleven are identical with species now living. Some few of these eleven
shells may possibly still linger in the depths of the Mediterranean, like
Murex vaginatus, see Fig. 132. The last-mentioned shell had already
become rare when the associated marine and volcanic strata above alluded
to were formed. On the whole, the modern character of the testaceous fauna
under consideration is expressed not only by the small proportion of extinct
species, but by the relative number of individuals by which most of the
other species are represented, for the proportion agrees with that observed
in the present fauna of the Mediterranean. The rarity of individuals in the
extinct species is such as to imply that they were already on the point of
dying out, having flourished chiefly in the earlier Pliocene times, when the
Subapennine strata were in progress.
Yet since the accumulation of these Newer Pliocene sands and clays, the
whole cone of Etna, 11,000 feet in height and about 90 miles in
circumference at its base, has been slowly built up; an operation requiring
many tens of thousands of years for its accomplishment, and to estimate the
magnitude of which it is necessary to study in detail the internal structure of
the mountain, and to see the proofs of its double axis, or the evidence of the
lavas of the present great centre of eruption having gradually overwhelmed
and enveloped a more ancient cone, situated 3½ miles to the east of the
present one.[4]
It appears that while Etna was increasing in bulk by a series of eruptions,
its whole mass, comprising the foundations of subaqueous origin above
alluded to, was undergoing a slow upheaval, by which those marine strata
were raised to the height of 1200 feet above the sea, as seen at Catera, and
perhaps to greater heights, for we cannot trace their extension westward,
owing to the dense and continuous covering of modern lava under which
they are buried. During the gradual rise of these Newer Pliocene formations
(consisting of clays, sands, and basalts) other strata of Post-pliocene date,
marine as well as fluviatile, accumulated round the base of the mountain,
and these, in their turn, partook of the upward movement, so that several
inland cliffs and terraces at low levels, due partly to the action of the sea
and partly to the river Simeto, originated in succession. Fossil remains of
the elephant, and other extinct quadrupeds, have been found in these Post-
Pliocene strata, associated with recent shells.

There is probably no part of Europe where the Newer Pliocene
formations enter so largely into the structure of the earth’s crust, or rise to
such heights above the level of the sea, as Sicily. They cover nearly half the
island, and near its centre, at Castrogiovanni, reach an elevation of 3000
feet. They consist principally of two divisions, the upper calcareous and the
lower argillaceous, both of which may be seen at Syracuse, Girgenti, and
Castrogiovanni. According to Philippi, to whom we are indebted for the
best account of the tertiary shells of this island, thirty-five species out of
one hundred and twenty-four obtained from the beds in central Sicily are
extinct.
A geologist, accustomed to see nearly all the Newer Pliocene formations
in the north of Europe occupying low grounds and very incoherent in
texture, is naturally surprised to behold formations of the same age so solid
and stony, of such thickness, and attaining so great an elevation above the
level of the sea. The upper or calcareous member of this group in Sicily
consists in some places of a yellowish-white stone, like the Calcaire
Grossier of Paris; in others, of a rock nearly as compact as marble. Its
aggregate thickness amounts sometimes to 700 or 800 feet. It usually occurs
in regular horizontal beds, and is occasionally intersected by deep valleys,
such as those of Sortino and Pentalica, in which are numerous caverns. The
fossils are in every stage of preservation, from shells retaining portions of
their animal matter and colour to others which are mere casts. The
limestone passes downward into a sandstone and conglomerate, below
which is clay and blue marl, from which perfect shells and corals may be
disengaged. The clay sometimes alternates with yellow sand.
South of the plain of Catania is a region in which the tertiary beds are
intermixed with volcanic matter, which has been for the most part the
product of submarine eruptions. It appears that, while the clay, sand, and
yellow limestone before mentioned were in course of deposition at the
bottom of the sea, volcanoes burst out beneath the waters, like that of
Graham Island, in 1831, and these explosions recurred again and again at
distant intervals of time. Volcanic ashes and sand were showered down and
spread by the waves and currents so as to form strata of tuff, which are
found intercalated between beds of limestone and clay containing marine
shells, the thickness of the whole mass exceeding 2000 feet. The fissures
through which the lava rose may be seen in many places, forming what are
called dikes.

No shell is more conspicuous in these Sicilian strata than the great
scallop, Pecten jacobæus (Fig. 133), now so common in the neighbouring
seas. The more we reflect on the preponderating number of this and other
recent shells, the more we are surprised at the great thickness, solidity, and
height above the sea of the rocky masses in which they are entombed, and
the vast amount of geographical change which has taken place since their
origin. It must be remembered that, before they began to emerge, the
uppermost strata of the whole must have been deposited under water. In
order, therefore, to form a just conception of their antiquity, we must first
examine singly the innumerable minute parts of which the whole is made
up, the successive beds of shells, corals, volcanic ashes, conglomerates, and
sheets of lava; and we must afterwards contemplate the time required for
the gradual upheaval of the rocks, and the excavation of the valleys. The
historical period seems scarcely to form an appreciable unit in this
computation, for we find ancient Greek temples, like those of Girgenti
(Agrigentum), built of the modern limestone of which we are speaking, and
resting on a hill composed of the same; the site having remained to all
appearances unaltered since the Greeks first colonised the island.
It follows, from the modern geological date of these rocks, that the fauna
and flora of a large part of Sicily are of higher antiquity than the country
itself. The greater part of the island has been raised above the sea since the
epoch of existing species, and the animals and plants now inhabiting it must

have migrated from adjacent countries, with whose productions the species
are now identical. The average duration of species would seem to be so
great that they are destined to outlive many important changes in the
configuration of the earth’s surface, and hence the necessity for those
innumerable contrivances by which they are enabled to extend their range
to new lands as they are formed, and to escape from those which sink
beneath the sea.
Newer Pliocene Strata of the Upper Val D’arno.—When we ascend
the Arno for about ten miles above Florence, we arrive at a deep narrow
valley called the Upper Val d’Arno, which appears once to have been a
lake, at a time when the valley below Florence was an arm of the sea. The
horizontal lacustrine strata of this upper basin are twelve miles long and
two broad. The depression which they fill has been excavated out of Eocene
and Cretaceous rocks, which form everywhere the sides of the valley in
highly inclined stratification. The thickness of the more modern and
unconformable beds is about 750 feet, of which the upper 200 feet consist
of Newer Pliocene strata, while the lower are Older Pliocene. The newer
series are made up of sands and a conglomerate called “sansino.” Among
the imbedded fossil mammalia are Mastodon arvernensis, Elephas
meridionalis, Rhinoceros etruscus, Hippopotamus major, and remains of the
genera bear, hyæna, and felis, nearly all of which occur in the Cromer
forest-bed (see Chap. 13, p. 191).
In the same upper strata are found, according to M. Gaudin, the leaves
and cones of Glyptostrobus europæus, a plant closely allied to G.
heterophyllus, now inhabiting the north of China and Japan. This conifer
had a wide range in time, having been traced back to the Lower Miocene
strata of Switzerland, and being common at Œningen in the Upper Miocene,
as we shall see in the sequel (p. 218).
Older Pliocene of Italy.—Subapennine Strata.—The Apennines, it is
well-known, are composed chiefly of Secondary or Mesozoic rocks,
forming a chain which branches off from the Ligurian Alps and passes
down the middle of the Italian peninsula. At the foot of these mountains, on
the side both of the Adriatic and the Mediterranean, are found a series of
tertiary strata, which form, for the most part, a line of low hills occupying
the space between the older chain and the sea. Brocchi was the first Italian
geologist who described this newer group in detail, giving it the name of the

Subapennine. Though chiefly composed of Older Pliocene strata, it belongs,
nevertheless, in part, both to older and newer members of the tertiary series.
The strata, for example, of the Superga, near Turin, are Miocene; those of
Asti and Parma Older Pliocene, as is the blue marl of Sienna; while the
shells of the incumbent yellow sand of the same territory approach more
nearly to the recent fauna of the Mediterranean, and may be Newer
Pliocene.
We have seen that most of the fossil shells of the Older Pliocene strata of
Suffolk which are of recent species are identical with testacea now living in
British seas, yet some of them belong to Mediterranean species, and a few
even of the genera are those of warmer climates. We might therefore expect,
in studying the fossils of corresponding age in countries bordering the
Mediterranean, to find among them some species and genera of warmer
latitudes. Accordingly, in the marls belonging to this period at Asti, Parma,
Sienna, and parts of the Tuscan and Roman territories, we observe the
genera Conus, Cypræa, Strombus, Pyrula, Mitra, Fasciolaria, Sigaretus,
Delphinula, Ancillaria, Oliva, Terebellum, Terebra, Perna, Plicatula, and
Corbis, some characteristic of tropical seas, others represented by species
more numerous or of larger size than those now proper to the
Mediterranean.
Older Pliocene Flora of Italy.—I have already alluded to the Newer
Pliocene deposits of the Upper Val d’Arno above Florence, and stated that
below those sands and conglomerates, containing the remains of the
Elephas meridionalis and other associated quadrupeds, lie an older
horizontal and conformable series of beds, which may be classed as Older
Pliocene. They consist of blue clays with some subordinate layers of lignite,
and exhibit a richer flora than the overlying Newer Pliocene beds, and one
receding farther from the existing vegetation of Europe. They also comprise
more species common to the antecedent Miocene period. Among the genera
of flowering plants, M. Gaudin enumerates pine, oak, evergreen oak, plum,
plane, alder, elm, fig, laurel, maple, walnut, birch, buckthorn, hickory,
sumach, sarsaparilla, sassafras, cinnamon, Glyptostrobus, Taxodium,
Sequoia, Persea, Oreodaphne (Fig. 134), Cassia, and Psoralea, and some
others. This assemblage of plants indicates a warm climate, but not so
subtropical an one as that of the Upper Miocene period, which will
presently be considered.

ig. 134: Creodaphne Heerii.
Leaf[5]
Fig. 135: Liquidambar europæum, var. trilobatum, A. Br. (sometimes
four-lobed, and more commonly five-lobed).
a. Leaf. b. Part of same. c. Fruit. d. Seed Œningen.

M. Gaudin, jointly with the Marquis Strozzi, has thrown much light on
the botany of beds of the same age in another part of Tuscany, at a place
called Montajone, between the rivers Elsa and Evola, where, among other
plants, is found the Oreodaphne Heerii, Gaud. (see Fig. 134), which is
probably only a variety of Oreodaphne foetens, or the laurel called the Til in
Madeira, where, as in the Canaries, it constitutes a large portion of the
native woods, but cannot now endure the climate of Europe. In the fossil
specimens the same glands or protuberances are preserved[6] (see Fig. 134)
as those which are seen in the axils of the primary veins of the leaves in the
recent Til. Another plant also indicating a warmer climate is the
Liquidambar europæum, Brong. (see Fig. 135), a species nearly allied to L.
styracifluum, L., which flourishes in most places in the Southern States of
North America, on the borders of the Gulf of Mexico.
[1] See Antiquity of Man, chap. xiv.

[2] Ehrenberg proposed in 1831 the term Bryozoum, or “Moss-animal,” for the
molluscous or ascidian form of polyp, characterised by having two openings to
the digestive sack, as in Eschara, Flustra, Retepora, and other zoophytes

popularly included in the corals, but now classed by naturalists as mollusca. The
term Polyzoum, synonymous with Bryozoum, was, it seems, proposed in 1830, or
the year before, by Mr. J. O. Thompson.

[3] E. Forbes Mem. Geol. Survey of Gt. Brit., vol. i, p. 386.

[4] See a Memoir on the Lavas and Mode of Origin of Mount Etna by the Author
in Phil. Trans., 1858.

[5] Feuilles fossiles de la Toscane.

[6] Contributions à la Flore fossile Italienne. Gaudin and Strozzi. Plate 11, Fig. 3.
Gaudin, p. 22.

CHAPTER XIV.
MIOCENE PERIOD—UPPER MIOCENE.

Upper Miocene Strata of France—Faluns of Touraine. —
Tropical Climate implied by Testacea. — Proportion of
recent Species of Shells. — faluns more ancient than the
Suffolk Crag. — Upper Miocene of Bordeaux and the South
of France. — Upper Miocene of Œningen, in Switzerland.
— Plants of the Upper Fresh-water Molasse. — Fossil Fruit
and Flowers as well as Leaves. — Insects of the Upper
Molasse. — Middle or Marine Molasse of Switzerland. —
Upper Miocene Beds of the Bolderberg, in Belgium. —
Vienna Basin. — Upper Miocene of Italy and Greece. —
Upper Miocene of India; Siwalik Hills. — Older Pliocene
and Miocene of the United States.

Upper Miocene Strata of France—Faluns of Touraine.—The strata
which we meet with next in the descending order are those called by many
geologists “Middle Tertiary,” for which in 1833 I proposed the name of
Miocene, selecting the “faluns” of the valley of the Loire, in France, as my
example or type. I shall now call these falunian deposits Upper Miocene, to
distinguish them from others to which the name of Lower Miocene will be
given.
No British strata have a distinct claim to be regarded as Upper Miocene,
and as the Lower Miocene are also but feebly represented in the British
Isles, we must refer to foreign examples in illustration of this important
period in the earth’s history. The term “faluns” is given provincially by
French agriculturists to shelly sand and marl spread over the land in
Touraine, just as similar shelly deposits were formerly much used in Suffolk
to fertilise the soil, before the coprolitic or phosphatic nodules came into

use. Isolated masses of such faluns occur from near the mouth of the Loire,
in the neighbourhood of Nantes, to as far inland as a district south of Tours.
They are also found at Pontlevoy, on the Cher, about seventy miles above
the junction of that river with the Loire, and thirty miles south-east of
Tours. Deposits of the same age also appear under new mineral conditions
near the towns of Dinan and Rennes, in Brittany. I have visited all the
localities above enumerated, and found the beds on the Loire to consist
principally of sand and marl, in which are shells and corals, some entire,
some rolled, and others in minute fragments. In certain districts, as at Doué,
in the Department of Maine and Loire, ten miles south-west of Saumur,
they form a soft building-stone, chiefly composed of an aggregate of broken
shells, bryozoa, corals, and echinoderms, united by a calcareous cement; the
whole mass being very like the Coralline Crag near Aldborough, and
Sudbourn in Suffolk. The scattered patches of faluns are of slight thickness,
rarely exceeding fifty feet; and between the district called Sologne and the
sea they repose on a great variety of older rocks; being seen to rest
successively upon gneiss, clay-slate, various secondary formations,
including the chalk; and, lastly, upon the upper fresh-water limestone of the
Parisian tertiary series, which, as before mentioned (p. 142), stretches
continuously from the basin of the Seine to that of the Loire.

At some points, as at Louans, south of Tours, the shells are stained of a
ferruginous colour, not unlike that of the Red Crag of Suffolk. The species
are, for the most part, marine, but a few of them belong to land and
fluviatile genera. Among the former, Helix turonensis) (Fig. 38) is the most
abundant. Remains of terrestrial quadrupeds are here and there intermixed,
belonging to the genera Dinotherium (Fig. 136), Mastodon, Rhinoceros,

Hippopotamus, Chæropotamus, Dichobune, Deer, and others, and these are
accompanied by cetacea, such as the Lamantin, Morse, Sea-calf, and
Dolphin, all of extinct species.
The fossil testacea of the faluns of the Loire imply, according to the late
Edward Forbes, that the beds were formed partly on the shore itself at the
level of low water, and partly at very moderate depths, not exceeding ten
fathoms below that level. The molluscan fauna is, on the whole, much more
littoral than that of the Pliocene Red and Coralline Crag of Suffolk, and
implies a shallower sea. It is, moreover, contrasted with the Suffolk Crag by
the indications it affords of an extra-European climate. Thus it contains
seven species of Cypræa, some larger than any existing cowry of the
Mediterranean, several species of Oliva, Ancillaria, Mitra, Terebra, Pyrula,
Fasciolaria, and Conus. Of the cones there are no less than eight species,
some very large, whereas the only European cone now living is of
diminutive size. The genus Nerita, and many others, are also represented by
individuals of a type now characteristic of equatorial seas, and wholly
unlike any Mediterranean forms. These proofs of a more elevated
temperature seem to imply the higher antiquity of the faluns as compared
with the Suffolk Crag, and are in perfect accordance with the fact of the
smaller proportion of testacea of recent species found in the faluns.
Out of 290 species of shells, collected by myself in 1840 at Pontlevoy,
Louans, Bossée, and other villages twenty miles south of Tours, and at
Savigné, about fifteen miles north-west of that place, seventy-two only
could be identified with recent species, which is in the proportion of
twenty-five per cent. A large number of the 290 species are common to all
the localities, those peculiar to each not being more numerous than we
might expect to find in different bays of the same sea.
The total number of species of testaceous mollusca from the faluns in my
possession is 302, of which forty-five only, or fourteen per cent, were found
by Mr. Wood to be common to the Suffolk Crag. The number of corals,
including bryozoa and zoantharia, obtained by me at Doué and other
localities before adverted to, amounts to forty-three, as determined by Mr.
Lonsdale, of which seven (one of them a zoantharian) agree specifically
with those of the Suffolk Crag. Some of the genera occurring fossil in
Touraine, as the corals Astrea and Dendrophyllia, and the bryozoan
Lunulites, have not been found in European seas north of the

Mediterranean; nevertheless, the zoantharia of the faluns do not seem to
indicate, on the whole, so warm a climate as would be inferred from the
shells.
It was stated that, on comparing about 300 species of Touraine shells
with about 450 from the Suffolk Crag, forty-five only were found to be
common to both, which is in the proportion of only fifteen per cent. The
same small amount of agreement is found in the corals also. I formerly
endeavoured to reconcile this marked difference in species with the
supposed co-existence of the two faunas, by imagining them to have
severally belonged to distinct zoological provinces or two seas, the one
opening to the north and the other to the south, with a barrier of land
between them, like the Isthmus of Suez, now separating the Red Sea and the
Mediterranean. But I now abandon that idea for several reasons; among
others, because I succeeded in 1841 in tracing the Crag fauna southward in
Normandy to within seventy miles of the Falunian type, near Dinan, yet
found that both assemblages of fossils retained their distinctive characters,
showing no signs of any blending of species or transition of climate.
The principal grounds, however, for referring the English Crag to the
older Pliocene and the French faluns to the Upper Miocene epochs, consist
in the predominance of fossil shells in the British strata identifiable with
species not only still living, but which are now inhabitants of neighbouring
seas, while the accompanying extinct species are of genera such as
characterise Europe. In the faluns, on the contrary, the recent species are in
a decided minority; and most of them are now inhabitants of the
Mediterranean, the coast of Africa, and the Indian Ocean; in a word, less
northern in character, and pointing to the prevalence of a warmer climate.
They indicate a state of things receding farther from the present condition
of Central Europe in physical geography and climate, and doubtless,
therefore, receding farther from our era in time.

Among the conspicuous fossils common to the faluns of the Loire and
the Suffolk Crag is a variety of the Voluta Lamberti, a shell already alluded
to (Fig. 123). The specimens of this shell which I have myself collected in
Touraine, or have seen in museums, are thicker and heavier than British
individuals of the same species, and shorter in proportion to their width, and
have the folds on the columella less oblique, as represented in Fig. 137.
Upper Miocene of Bordeaux and the South of France.—A great extent
of country between the Pyrenees and the Gironde is overspread by tertiary
deposits of various ages, and chiefly of Miocene date. Some of these, near
Bordeaux, coincide in age with the faluns of Touraine, already mentioned,
but many of the species of shells are peculiar to the south. The succession
of beds in the basin of the Gironde implies several oscillations of level by
which the same wide area was alternately converted into sea and land and
into brackish-water lagoons, and finally into fresh-water ponds and lakes.
Among the fresh-water strata of this age near the base of the Pyrenees are
marls, limestones and sands, in which the eminent comparative anatomist,
M. Lartet, has obtained a great number of fossil mammalia common to the
faluns of the Loire and the Upper Miocene beds of Switzerland, such as
Dinotherium giganteum and Mastodon angustidens; also the bones of
quadrumana, or of the ape and monkey tribe, which were discovered in
1837, the first of that order of quadrupeds detected in Europe. They were
found near Auch, in the Department of Gers, in latitude 43° 39′ N. About
forty miles west of Toulouse. They were referred by MM. Lartet and

Blainville to a genus closely allied to the Gibbon, to which they gave the
name of Pliopithecus. Subsequently, in 1856, M. Lartet described another
species of the same family of long-armed apes (Hylobates), which he
obtained from strata of the same age at Saint-Gaudens, in the Haute
Garonne. The fossil remains of this animal consisted of a portion of a lower
jaw with teeth and the shaft of a humerus. It is supposed to have been a
tree-climbing frugivorous ape, equalling man in stature. As the trunks of
oaks are common in the lignite beds in which it lay, it has received the
generic name of Dryopithecus. The angle formed by the ascending ramus of
the jaw and the alveolar border is less open, and therefore more like the
human subject, than in the Chimpanzee, and what is still more remarkable,
the fossil, a young but adult individual, had all its milk teeth replaced by the
second set, while its last true molar (or wisdom-tooth) was still
undeveloped, or only existed as a germ in the jaw-bone. In the mode,
therefore, of the succession of its teeth (which, as in all the old-World apes,
exactly agree in number with those in man) it differed from the Gorilla and
Chimpanzee, and corresponded with the human species.
Upper Miocene Beds of Œningen, in Switzerland.—The faluns of the
Loire first served, as already stated (p. 211), as the type of the Miocene
formations in Europe. They yielded a plentiful harvest of marine fossil
shells and corals, but were entirely barren of plants and insects. In
Switzerland, on the other hand, deposits of the same age have been
discovered, remarkable for their botanical and entomological treasures. We
are indebted to Professor Heer, of Zurich, for the description, restoration,
and classification of several hundred species and varieties of these fossil
plants, the whole of which he has illustrated by excellent figures in his
“Flora Tertiaria Helvetiæ.” This great work, and those of Adolphe
Brongniart, Unger, Goppert and others, show that this class of fossils is
beginning to play the same important part in the classification of the tertiary
strata containing lignite or brown coal as an older flora has long played in
enabling us to understand the ancient coal or carboniferous formation. No
small skepticism has always prevailed among botanists as to whether the
leaves alone and the wood of plants could ever afford sufficient data for
determining even genera and families in the vegetable kingdom. In truth,
before such remains could be rendered available a new science had to be
created. It was necessary to study the outlines, nervation, and microscopic
structure of the leaves, with a degree of care which had never been called

for in the classification of living plants, where the flower and fruit afforded
characters so much more definite and satisfactory. As geologists, we cannot
be too grateful to those who, instead of despairing when so difficult a task
was presented to them, or being discouraged when men of the highest
scientific attainments treated the fossil leaves as worthless, entered with full
faith and enthusiasm into this new and unexplored field. That they should
frequently have fallen into errors was unavoidable, but it is remarkable,
especially if we inquire into the history of Professor Heer’s researches, how
often early conjectures as to the genus and family founded on the leaves
alone were afterwards confirmed when fuller information was obtained. As
examples to be found on comparing Heer’s earlier and later works, I may
instance the chestnut, elm, maple, cinnamon, magnolia, buckbean or
Menyanthes, vine, buckthorn (Rhamnus), Andromeda and Myrica, and
among the conifers Sequoia and Taxodium. In all these cases the plants
were first recognised by their leaves, and the accuracy of the determination
was afterwards confirmed when the fruit, and in some instances both fruit
and flower, were found attached to the same stem as the leaves.
But let us suppose that no fruit, seed, or flower had ever been met with in
a fossil state, we should still have been indebted to the persevering labours
of botanical palæontologists for one of the grandest scientific discoveries
for which the present century is remarkable—namely, the proofs now
established of the prevalence of a mild climate and a rich arborescent flora
in the arctic regions in that Miocene epoch on the history of which we are
now entering. It may be useful if I endeavour to give the reader in a few
words some idea of the nature of the evidence of these important
conclusions, to show how far they may be safely based on fossil leaves
alone. When we begin by studying the fossils of the Newer Pliocene
deposits, such as those of the Upper Val d’Arno, before alluded to, we
perceive that the fossil foliage agrees almost entirely with the trees and
shrubs of a modern European forest. In the plants of the Older Pliocene
strata of the same region we observe a larger proportion of species and
genera which, although they may agree with well-known Asiatic or other
foreign types, are at present wanting in Italy. If we then examine the
Miocene formations of the same country, exotic forms become more
abundant, especially the palms, whether they belong to the European or
American fan-palms, Chamærops and Sabal, or to the more tropical family
of the date-palms or Phœnicites, which last are conspicuous in the Lower

Miocene beds of Central Europe. Although we have not found the fruit or
flower of these palms in a fossil state, the leaves are so characteristic that no
one doubts the family to which they belong, or hesitates to accept them as
indications of a warm and sub-tropical climate.
When the Miocene formations are traced to the northward of the 50th
degree of latitude, the fossil palms fail us, but the greater proportion of the
leaves, whether identical with those of existing European trees or of forms
now unknown in Europe, which had accompanied the Miocene palms, still
continue to characterise rocks of the same age, until we meet with them not
only in Iceland, but in Greenland, in latitude 70° N., and in Spitzbergen,
latitude 78° 56′, or within about 11 degrees of the pole, and under
circumstances which clearly show them to have been indigenous in those
regions, and not to have been drifted from the south (see p. 240). Not only,
therefore, has the botanist afforded the geologist much palæontological
assistance in identifying distinct tertiary formations in distant places by his
power of accurately discriminating the forms, veining, and microscopic
structure of leaves or wood, but, independently of that exact knowledge
derivable from the organs of fructification, we are indebted to him for one
of the most novel, unexpected results of modern scientific inquiry.
The Miocene formations of Switzerland have been called Molasse, a term
derived from the French mol, and applied to a soft, incoherent, greenish
sandstone, occupying the country between the Alps and the Jura. This
molasse comprises three divisions, of which the middle one is marine, and
being closely related by its shells to the faluns of Touraine, may be classed
as Upper Miocene. The two others are fresh-water, the upper of which may
be also grouped with the faluns, while the lower must be referred to the
Lower Miocene, as defined in the next chapter.
Upper Fresh-water Molasse.—This formation is best seen at Œningen,
in the valley of the Rhine, between Constance and Schaffhausen, a locality
celebrated for having produced in the year 1700 the supposed human
skeleton called by Scheuchzer “homo diluvii testis,” a fossil afterwards
demonstrated by Cuvier to be a reptile, or aquatic salamander, of larger
dimensions than even its great living representative, the salamander of
Japan.
The Œningen strata consist of a series of marls and limestones, many of
them thinly laminated, and which appear to have slowly accumulated in a

lake probably fed by springs holding carbonate of lime in solution. The
elliptical area over which this fresh-water formation has been traced
extends, according to Sir Roderick Murchison, for a distance of ten miles
east and west from Berlingen, on the right bank of the river to Wangen, and
to Œningen, near Stein, on the left bank. The organic remains have been
chiefly derived from two quarries, the lower of which is about 550 feet
above the level of the Lake of Constance, while the upper quarry is 150 feet
higher. In this last, a section thirty feet deep displays a great succession of
beds, most of them splitting into slabs and some into very thin laminæ.
Twenty-one beds are enumerated by Professor Heer, the uppermost a
bluish-grey marl seven feet thick, with organic remains, resting on a
limestone with fossil plants, including leaves of poplar, cinnamon, and
pond-weed (Potamogeton), together with some insects; while in the bed No.
4, below, is a bituminous rock, in which the Mastodon tapiroides, a
characteristic Upper Miocene quadruped, has been met with. The 5th bed,
two or three inches thick, contains fossil fish, e.g., Leuciscus (roach), and
the larvæ of dragon-flies, with plants such as the elm (Ulmus), and the
aquatic Chara. Below this are other plant-beds; and then, in No. 9, the stone
in which the great salamander (Andrias Scheuchzeri) and some fish were
found. Below this other strata occur with fish, tortoises, the great
salamander before alluded to, fresh-water mussels, and plants. In No. 16 the
fossil fox of Œningen, Galecynus Œningensis, Owen, was obtained by Sir
R. Murchison. To this succeed other beds with mammalia (Lagomys),
reptiles, (Emys), fish, and plants, such as walnut, maple, and poplar. In the
19th bed are numerous fish, insects, and plants, below which are marls of a
blue indigo colour.
In the lower quarry eleven beds are mentioned, in which, as in the upper,
both land and fresh-water plants and many insects occur. In the 6th,
reckoning from the top, many plants have been obtained, such as
Liquidambar, Daphnogene, Podogonium, and Ulmus, together with
tortoises, besides the bones and teeth of a ruminant quadruped, named by H.
von Meyer Palæomeryx eminens. No. 9 is called the insect-bed, a layer only
a few inches thick, which, when exposed to the frost, splits into leaves as
thin as paper. In these thin laminæ plants such as Liquidambar,
Daphnogene, and Glyptostrobus, occur, with innumerable insects in a
wonderful state of preservation, usually found singly. Below this is an

indigo-blue marl, like that at the bottom of the higher quarry, resting on
yellow marl ascertained to be at least thirty feet thick.

All the above fossil-bearing strata were evidently formed with extreme
slowness. Although the fossiliferous beds are, in the aggregate, no more
than a few yards in thickness, and have only been examined in the small
area comprised in the two quarries just alluded to, they give us an insight
into the state of animal and vegetable life in part of the Upper Miocene
period, such as no other region in the world has elsewhere supplied. In the
year 1859, Professor Heer had already determined no less than 475 species
of plants and more than 800 insects from these Œningen beds. He supposes
that a river entering a lake floated into it some of the leaves and land
insects, together with the carcasses of quadrupeds, among others a great
Mastodon. Occasionally, during tempests, twigs and even boughs of trees
with their leaves were torn off and carried for some distance so as to reach
the lake. Springs, containing carbonate of lime, seem at some points to have
supplied calcareous matter in solution, giving origin locally to a kind of
travertin, in which organic bodies sinking to the bottom became
hermetically sealed up. The laminæ, says Heer, which immediately succeed
each other were not all formed at the same season, for it can be shown that,
when some of them originated, certain plants were in flower, whereas, when
the next of these layers was produced, the same plants had ripened their
fruit. This inference is confirmed by independent proofs derived from
insects. The principal insect-bed is rarely two inches thick, and is

composed, says Heer, of about 250 leaf-like laminæ, some of which were
deposited in the spring, when the Cinnamomum polymorphum (Fig. 138)
was in flower, others in summer, when winged ants were numerous, and
when the poplar and willow had matured their seed; others, again, in
autumn, when the same Cinnamomum polymorphum (Fig. 138) was in fruit,
as well as the liquidambar, oak, clematis, and many other plants. The
ancient lake seems to have had a belt of poplars and willows round its
borders, countless leaves of which were imbedded in mud, and together
with them, at some points, a species of reed, Arundo, which was very
common.
One of the most characteristic shrubs is a papilionaceous and leguminous
plant of an extinct genus, called by Heer Podogonium, of which two species
are known. Entire twigs have been found with flowers, and always without
leaves, as the flowers evidently came out, as in the poplar and willow tribe,
before any leaves made their appearance. Other specimens have been
obtained with ripe fruits accompanied by leaves, which resemble those of
the tamarind, to which it was evidently allied, being of the family
Cæsalpineæ, now proper to warmer regions.

The Upper Miocene flora of Œningen is peculiarly important, in
consequence of the number of genera of which not merely the leaves, but,
as in the case of the Podogonium just mentioned, the fruit also and even the
flower are known. Thus there are nineteen species of maple, ten of which

have already been found with fruit. Although in no one region of the globe
do so many maples now flourish, we need not suspect Professor Heer of
having made too many species in this genus when we consider the manner
in which he has dealt with one of them, Acer trilobatum, Figs. 139 and 140.
Of this plant the number of marked varieties figured and named is very
great, and no less than three of them had been considered as distinct species
by other botanists, while six of the others might have laid claim, with nearly
equal propriety, to a like distinction. The common form, called Acer
trilobatum, Fig. 139, may be taken as a normal representative of the
Œningen fossil, and Fig. 140, as one of the most divergent varieties, having
almost four lobes in the leaf instead of three.

Among the conspicuous genera which abounded in the Miocene period in
Europe is the plane-tree, Platanus, the fossil species being considered by
Heer to come nearer to the American P. occidentalis than to P. orientalis of
Greece and Asia Minor. In some of the fossil specimens the male flowers
are preserved. Among other points of resemblance with the living plane-
trees, as we see them in the parks and squares of London, fossil fragments
of the trunk are met with, having pieces of their bark peeling off.

The vine of Œningen, Vitis teutonica, Ad. Brong, is of a North American
type. Both the leaves and seeds have been found at Œningen, and bunches
of compressed grapes of the same species have been met with in the brown
coal of Wetteravia in Germany. No less than eight species of smilax, a
monocotyledonous genus, occur at Œningen and in other Upper Miocene
localities, the flowers of some of them, as well as the leaves, being
preserved; as in the case of the very common fossil, S. sagittifera, Fig. 142,
a.
Leaves of plants supposed to belong to the order Proteaceæ have been
obtained partly from Œningen and partly from the lacustrine formation of
the same age at Locle in the Jura. They have been referred to the genera
Banksia, Grevillea, Hakea, and Persoonia. Of Hakea there is the impression
of a supposed seed-vessel, with its characteristic thick stalk and seeds, but
as the fruit is without structure, and has not yet been found attached to the
same stem as the leaf, the proof is incomplete.

To whatever family the foliage hitherto regarded as proteaceous by many
able palæontologists may eventually be shown to belong, we must be
careful not to question their affinity to that order of plants on those
geographical considerations which have influenced some botanists. The
nearest living Proteaceæ now feel the in Abyssinia in lat. 20° N., but the
greatest number are confined to the Cape and Australia. The ancestors,
however, of the Œningen fossils ought not to be looked for in such distant
regions, but from that European land which in Lower Miocene times bore
trees with similar foliage, and these had doubtless an Eocene source, for
cones admitted by all botanists to be proteaceous have been met with in one
division of that older Tertiary group (see Fig. 206). The source of these last,
again, must not be sought in the antipodes, for in the white chalk of Aix-la-
Chapelle leaves like those of Grevillea and other proteaceous genera have
been found in abundance, and, as we shall see (p. 304) in a most perfect
state of preservation. All geologists agree that the distribution of the
Cretaceous land and sea had scarcely any connection with the present
geography of the globe.

In the same beds with the supposed Proteaceæ there occurs at Locle a
fan-palm of the American type Sabal (for genus see Fig. 151), a genus
which ranges throughout the low country near the sea from the Carolinas to
Florida and Louisiana. Among the Coniferæ of Upper Miocene age is found
a deciduous cypress nearly allied to the Taxodium distichum of North
America, and a Glyptostrobus (Fig. 144), very like the Japanese G.
heterophyllus, now common in our shrubberies.

Before the appearance of Heer’s work on the Miocene Flora of
Switzerland, Unger and Goppert had already pointed out the large
proportion of living North American genera which distinguished the
vegetation of the Miocene period in Central Europe. Next in number, says
Heer, to these American forms at Œningen the European genera
preponderate, the Asiatic ranking in the third, the African in the fourth, and
the Australian in the fifth degree. The American forms are more numerous
than in the Italian Pliocene flora, and the whole vegetation indicates a
warmer climate than the Pliocene, though not so high a temperature as that
of the older or Lower Miocene period.
The conclusions drawn from the insects are for the most part in perfect
harmony with those derived from the plants, but they have a somewhat less
tropical and less American aspect, the South European types being more
numerous. On the whole, the insect fauna is richer than that now inhabiting
any part of Europe. No less than 844 species are reckoned by Heer from the
Œningen beds alone, the number of specimens which he has examined
being 5080. The entire list of Swiss species from the Upper and Lower
Miocene together amount to 1322. Almost all the living families of
Coleoptera are represented, but, as we might have anticipated from the
preponderance of arborescent and ligneous plants, the wood-eating beetles

play the most conspicuous part, the Buprestidæ and other long-horned
beetles being particularly abundant.
The patterns and some remains of the colours both of Coleoptera and
Hemiptera are preserved at Œningen, as, for example in Harpactor (Fig.
145), in which the antennæ, one of the eyes, and the legs and wings are
retained. The characters, indeed, of many of the insects are so well defined
as to incline us to believe that if this class of the invertebrata were not so
rare and local, they might be more useful than even the plants and shells in
settling chronological points in geology.
Middle or Marine Molasse (Upper Miocene) of Switzerland.—It was
before stated that the Miocene formation of Switzerland consisted of, first,
the upper fresh-water molasse, comprising the lacustrine marls of Œningen;
secondly, the marine molasse, corresponding in age to the faluns of
Touraine; and thirdly, the lower fresh-water molasse. Some of the beds of
the marine or middle series reach a height of 2470 feet above the sea. A
large number of the shells are common to the faluns of Touraine, the Vienna
basin, and other Upper Miocene localities. The terrestrial plants play a
subordinate part in the fossiliferous beds, yet more than ninety of them are
enumerated by Heer as belonging to this falunian division, and of these
more than half are common to subjacent Lower Miocene beds, while a
proportion of about forty-five in one hundred are common to the overlying
Œningen flora. Twenty-six of the ninety-two species are peculiar.

Upper Miocene of the Bolderberg, in Belgium.—In a small hill or
ridge called the Bolderberg, which I visited in 1851, situated near Hasselt,
about forty miles E.N.E. of Brussels, strata of sand and gravel occur, to
which M. Dumont first called attention as appearing to constitute a northern
representative of the faluns of Touraine. On the whole, they are very distinct
in their fossils from the two upper divisions of the Antwerp Crag before
mentioned (p. 204), and contain shells of the genera Oliva, Conus,
Ancillaria, Pleurotoma, and Cancellaria in abundance. The most common
shell is an Olive (Fig. 146), called by Nyst Oliva Dufresnii; and
constituting, as M. Bosquet observes, a smaller and shorter variety of the
Bordeaux species.
So far as the shells of the Bolderberg are known, the proportion of recent
species agrees with that in the faluns of Touraine, and the climate must have
been warmer than that of the Coralline Crag of England.
Upper Miocene Beds of the Vienna Basin.—In South Germany the
general resemblance of the shells of the Vienna tertiary basin with those of
the faluns of Touraine has long been acknowledged. In the late Dr. Hörnes’s
excellent work on the fossil mollusca of that formation, we see accurate
figures of many shells, clearly of the same species as those found in the
falunian sands of Touraine.
According to Professor Suess, the most ancient and purely marine of the
Miocene strata in this basin consist of sands, conglomerates, limestones,
and clays, and they are inclined inward, or from the borders of the trough
towards the centre, their outcropping edges rising much higher than the
newer beds, whether Miocene or Pliocene, which overlie them, and which
occupy a smaller area at an inferior elevation above the sea. M. Hornes has
described no less than 500 species of gasteropods, of which he identifies
one-fifth with living species of the Mediterranean, Indian, or African seas,

but the proportion of existing species among the lamellibranchiate bivalves
exceeds this average. Among many univalves agreeing with those of Africa
on the eastern side of the Atlantic are Cypræa sanguinolenta, Buccinum
lyratum, and Oliva flammulata. In the lowest marine beds of the Vienna
basin the remains of several mammalia have been found, and among them a
species of Dinotherium, a Mastodon of the Trilophodon family, a
Rhinoceros (allied to R. megarhinus, Christol), also an animal of the hog
tribe, Listriodon, von Meyer, and a carnivorous animal of the canine family.
The Helix turonensis (Fig. 38), the most common land shell of the French
faluns, accompanies the above land animals. In a higher member of the
Vienna Miocene series are found Dinotherium giganteum (Fig. 136),
Mastodon longirostris, Rhinoceros Schleiermacheri, Acerotherium
incisivum, and Hippotherium gracile, all of them equally characteristic of
an Upper Miocene deposit occurring at Eppelsheim, in Hesse Darmstadt; a
locality also remarkable as having furnished in latitude 49° 50′ N. the bone
of a large ape of the Gibbon kind, the most northerly example yet
discovered of a quadrumanous animal.

M. Alcide d’Orbigny has shown that the foraminifera of the Vienna basin
differ alike from the Eocene and Pliocene species, and agree with those of
the faluns, so far as the latter are known. Among the Vienna foraminifera,
the genus Amphistegina (Fig. 147) is very characteristic, and is supposed by
d’Archiac to take the same place among the Rhizopods of the Upper
Miocene era which the Nummulites occupy in the Eocene period.
The flora of the Vienna basin exhibits some species which have a general
range through the whole Miocene period, such as Cinnamomum
polymorphum (Fig. 138), and C. Scheuchzeri, also Planera Richardi, Mich.,
Liquidambar europæum (Fig. 135) Juglans bilinica, Cassia ambigua, and
C. lignitum. Among the plants common to the Upper Miocene beds of

Œningen, in Switzerland, are Platanus aceroides (Fig. 141), Myrica
vindobonensis, and others.
Upper Miocene Strata of Italy.—We are indebted to Signor Michelotti
for a valuable work on the Miocene shells of Northern Italy. Those found in
the hill called the Superga, near Turin, have long been known to correspond
in age with the faluns of Touraine, and they contain so many species
common to the Upper Miocene strata of Bordeaux as to lead to the
conclusion that there was a free communication between the northern part
of the Mediterranean and the Bay of Biscay in the Upper Miocene period.
Upper Miocene Formations of Greece.—At Pikermé, near Athens,
MM. Wagner and Roth have described a deposit in which they found the
remains of the genera Mastodon, Dinotherium, Hipparion, two species of
Giraffe, Antelope, and others, some living and some extinct. With them
were also associated fossil bones of the Semnopithecus, showing that here,
as in the south of France, the quadrumana were characteristic of this period.
The whole fauna attests the former extension of a vast expanse of grassy
plains where we have now the broken and mountainous country of Greece;
plains, which were probably united with Asia Minor, spreading over the
area where the deep Ægean Sea and its numerous islands are now situated.
We are indebted to M. Gaudry, who visited Pikermé, for a treatise on these
fossil bones, showing how many data they contribute to the theory of a
transition from the mammalia of the Upper Miocene through the Pliocene
and Post-pliocene forms to those of living genera and species.
Upper Miocene of India. Siwâlik Hills.—The Siwâlik Hills lie at the
southern foot of the Himalayan chain, rising to the height of 2000 and 3000
feet. Between the Jumna and the Ganges they consist of inclined strata of
sandstone, shingle, clay, and marl. We are indebted to the indefatigable
researches of Dr. Falconer and Sir Proby Cautley, continued for fifteen
years, for the discovery in these marls and sandstones of a great variety of
fossil mammalia and reptiles, together with many fresh-water shells. Out of
fifteen species of shells of the genera Paludina, Melania, Ampullaria, and
Unio, all are extinct or unknown species with the exception of four, which
are still inhabitants of Indian rivers. Such a proportion of living to extinct
mollusca agrees well with the usual character of an Upper Miocene or
Falunian fauna, as observed in Touraine, or in the basin of Vienna and
elsewhere.

The genera of mammalia point in the same direction. One of them, of the
genus Chalicotherium (or Anisodon of Lartet), is a pachyderm intermediate
between the Rhinoceros and Anoplothere, and characteristic of the Upper
Miocene strata of Eppelsheim, and of the south of France. With it occurs
also an extinct form of Hippopotamus, called Hexaprotodon, and a species
of Hippotherium and pig, also two species of Mastodon, two of elephant,
and three other elephantine proboscidians; none of them agreeing with any
fossil forms of Europe, and being intermediate between the genera Elephas
and Mastodon, constituting the sub-genus Stegodon of Falconer. With these
are associated a monkey, allied to the Semnopithecus entellus, now living in
the Himalaya, and many ruminants. Among these last, besides the giraffe,
camel, antelope, stag, and others, we find a remarkable new type, the
Sivatherium, like a gigantic four-horned deer. There are also new forms of
carnivora, both feline and canine, the Machairodus among the former, also
hyænas, and a subursine form called the Hyænarctos, and a genus allied to
the otter (Enhydriodon), of formidable size.
The giraffe, camel, and a large ostrich may be cited as proofs that there
were formerly extensive plains where now a steep chain of hills, with deep
ravines, runs for many hundred miles east and west. Among the
accompanying reptiles are several crocodiles, some of huge dimensions,
and one not distinguishable, says Dr. Falconer, from a species now living in
the Ganges (C. Gangeticus); and there is still another saurian which the
same anatomist has identified with a species now inhabiting India. There
was also an extinct species of tortoise of gigantic proportions
(Colossochelys Atlas), the curved shell of which was twelve feet three
inches long and eight feet in diameter, the entire length of the animal being
estimated at eighteen feet, and its probable height seven feet.
Numerous fossils of the Siwâlik type have also been found in Perim
Island, in the Gulf of Cambay, and among these a species of Dinotherium, a
genus so characteristic of the Upper Miocene period in Europe.
Older Pliocene and Miocene Formations in the United States.—
Between the Alleghany Mountains, formed of older rocks, and the Atlantic,
there intervenes, in the United States, a low region occupied principally by
beds of marl, clay, and sand, consisting of the cretaceous and tertiary
formations, and chiefly of the latter. The general elevation of this plain
bordering the Atlantic does not exceed 100 feet, although it is sometimes

several hundred feet high. Its width in the middle and southern states is very
commonly from 100 to 150 miles. It consists, in the South, as in Georgia,
Alabama, and South Carolina, almost exclusively of Eocene deposits; but in
North Carolina, Maryland, Virginia, Delaware, more modern strata
predominate, of the age of the English Crag and faluns of Touraine.[1]

In the Virginian sands, we find in great abundance a species of Astarte (A.
undulata, Conrad), which resembles closely, and may possibly be a variety
of, one of the commonest fossils of the Suffolk Crag (A. Omalii); the other
shells also, of the genera Natica, Fissurella, Artemis, Lucina, Chama,
Pectunculus, and Pecten, are analagous to shells both of the English Crag
and French faluns, although the species are almost all distinct. Out of 147 of
these American fossils I could only find thirteen species common to
Europe, and these occur partly in the Suffolk Crag, and partly in the faluns
of Touraine; but it is an important characteristic of the American group, that
it not only contains many peculiar extinct forms, such as Fusus
quadricostatus, Say (see Fig. 149), and Venus tridacnoides, abundant in
these same formations, but also some shells which, like Fulgur carica of
Say and F. canaliculatus (see Fig. 148), Calyptræa costata, Venus
mercenaria, Lam., Modiola glandula, Totten, and Pecten magellanicus,
Lam., are recent species, yet of forms now confined to the western side of
the Atlantic—a fact implying that some traces of the beginning of the
present geographical distribution of mollusca date back to a period as
remote as that of the Miocene strata.

Of ten species of corals which I procured on the banks of the James
River, one agrees generically with a coral now living on the coast of the
United States. Mr. Lonsdale regarded these corals as indicating a
temperature exceeding that of the Mediterranean, and the shells would lead
to similar conclusions. Those occurring on the James River are in the 37th
degree of N. latitude, while the French faluns are in the 47th; yet the forms
of the American fossils would scarcely imply so warm a climate as must
have prevailed in France when the Miocene strata of Touraine originated.
Among the remains of fish in these post-eocene strata of the United
States are several large teeth of the shark family, not distinguishable
specifically from fossils of the faluns of Touraine.
[1] Proceedings of the Geol. Soc., vol. iv, pt. iii, 1845, p. 547.

CHAPTER XV.
LOWER MIOCENE (OLIGOCENE OF BEYRICH).

Lower Miocene Strata of France. — Line between Miocene
and Eocene. — Lacustrine Strata of Auvergne. — Fossil
mammalia of the Limagne d’Auvergne. — Lower Molasse
of Switzerland. — Dense Conglomerates and Proofs of
Subsidence. — Flora of the Lower Molasse. — American
Character of the Flora. — Theory of a Miocene Atlantis. —
Lower Miocene of Belgium. — Rupelian Clay of Hermsdorf
near Berlin. — Mayence Basin. — Lower Miocene of
Croatia. — Oligocene Strata of Beyrich. — Lower Miocene
of Italy. — Lower Miocene of England. — Hempstead Beds.
— Bovey Tracey Lignites in Devonshire. — Isle of Mull
Leaf-Beds. — Arctic Miocene Flora. — Disco Island. —
Lower Miocene of United States. — Fossils of Nebraska.

Line between Miocene and Eocene Formations.—The marine faluns of
the valley of the Loire have been already described as resting in some
places on a fresh-water tertiary limestone, fragments of which have been
broken off and rolled on the shores and in the bed of the Miocene sea. Such
pebbles are frequent at Pontlevoy on the Cher, with hollows drilled in them
in which the perforating marine shells of the Falunian period still remain.
Such a mode of superposition implies an interval of time between the origin
of the fresh-water limestone and its submergence beneath the waters of the
Upper Miocene sea. The limestone in question forms a part of the formation
called the Calcaire de la Beauce, which constitutes a large table-land
between the basins of the Loire and the Seine. It is associated with marls
and other deposits, such as may have been formed in marshes and shallow
lakes in the newest part of a great delta. Beds of flint, continuous or in
nodules, accumulated in these lakes, and aquatic plants called Charae, left

their stems and seed-vessels imbedded both in the marl and flint, together
with fresh-water and land shells. Some of the siliceous rocks of this
formation are used extensively for mill-stones. The flat summits or
platforms of the hills round Paris, and large areas in the forest of
Fontainebleau, as well as the Plateau de la Beauce, already alluded to, are
chiefly composed of these fresh-water strata. Next to these in the
descending order are marine sands and sandstone, commonly called the
Gres de Fontainebleau, from which a considerable number of shells, very
distinct from those of the faluns, have been obtained at Etampes, south of
Paris, and at Montmartre and other hills in Paris itself, or in its suburbs. At
the bottom of these sands a green clay occurs, containing a small oyster,
Ostrea cyathula, Lam., which, although of slight thickness, is spread over a
wide area. This clay rests immediately on the Paris gypsum, or that series of
beds of gypsum and gypseous marl from which Cuvier first obtained
several species of Palæotherium and other extinct mammalia.[1]
At this junction of the clay and the gypsum the majority of French
geologists have always drawn the line between the Middle and Lower
Tertiary, or between the Miocene and Eocene formations, regarding the
Fontainebleau sands and the Ostrea cyathula clay as the base of the
Miocene, and the gypsum, with its mammalia, as the top of the Eocene
group. I formerly dissented from this division, but I now find that I must
admit it to be the only one which will agree with the distribution of the
Miocene mammalia, while even the mollusca of the Fontainebleau sands,
which were formerly supposed to present at preponderance of affinities to
an Eocene fauna, have since been shown to agree more closely with the
fossils of certain deposits always regarded as Middle Tertiary at Mayence
and in Belgium. In fact, we are now arriving at that stage of progress when
the line, wherever it be drawn between Miocene and Eocene, will be an
arbitrary one, or one of mere convenience, as I shall have an opportunity of
showing when the Upper Eocene formations in the Isle of Wight are
described in the sixteenth chapter.
Lower Miocene of Central France.—Lacustrine strata, belonging, for
the most part, to the same Miocene system as the Calcaire de la Beauce, are
again met with farther south in Auvergne, Cantal, and Vélay. They appear to
be the monuments of ancient lakes, which, like some of those now existing
in Switzerland, once occupied the depressions in a mountainous region, and
have been each fed by one or more rivers and torrents. The country where