The Student's Lyell. A manual of elementary geology. Edited by J. W. Judd. With ... illustrations, etc

Preface

The writings of Sir Charles Lyell occupy so undisputed a position among the classics of science that neither explanation nor apology is needed for the issue of the present work. Its aim is to present — in a form suitable alike for students and general readers — an embodiment of those principles of geological teaching which will always be identified with the name of Lyell. The ' Principles of Geology,' which appeared between the years 1830 and 1833, discussed the changes going on in the inorganic and organic world, as affording illustrations of the events which have taken place in past geological times ; the ' Elements of Geology,' published in 1838, aimed, on the other hand, at explaining the whole sequence of geological phenomena in the light of observations made upon the existing course of nature.

This latter book, of which the title was in 1851 changed to ' A Manual of Elementary Geology,' and which was in 1871 recast into a form more suitable for teaching purposes, under the name of ' The Student's Elements of Geology,' has formed the basis of the present volume ; where, however, it seemed to be desirable, passages have been included from the other "writings of the author. When Sir Leonard Lyell offered to place in my hands for revision these writings of his uncle, I could not but feel gratified as well as honoured by the trust ; for among my

PREFACE.

most cherished recollections are those days of constant and friendly intercourse with Sir Charles Lyell during the period he was engaged in writing the ' Student's Elements ' and in preparing the second edition. The progress of geological science, during the last quarter of a century, has rendered necessary very considerable additions and corrections, and the re-writing of large por tions of the book, but I haveeverywhere striven to preserve the author's plan and to follow the methods which charac terise the original work. In spite of the expansion of the text and the intro duction into it of more than one hundred new illustrations, it has nevertheless been found possible, by using smaller type for certain portions, to avoid increasing the bulk or the cost ofthe volume. It is hoped, moreover, that this employ ment of different kinds of type will afford some assistance to the student.

The beginner is advised, in his first perusal of the work, to devote his attention mainly to the portions printed in larger type ; and afterwards, in entering upon its more serious study, to read the whole through continuously. It may be well to mention, too, that although, for the very cogent reasons urged by Lyell (see p. 140), it is desirable in the first instance to study the newer and less altered strata before the older and greatly metamorphosed rocks, yet, in revising his studies at a later period, the reader may find it advantageous to take up the several systems in historical order. Some of the additional illustrations to the book have been taken from the writings of Lyell's lifelong friend and fellow-worker Poulett Scrope; for others my thanks are due to the Trustees of the British Museum and to Dr. Henry Woodward, to Professor 0. C. Marsh of Yale College, and to Dr. R. D. Roberts. The majority of the new illustrations have, however, been specially drawn for

PREFACE.

the work by Mr. Gilbert Cullis, and to that gentleman and to Dr. W. Fraser Hume I am also indebted for much care in reading portions of the proof-sheets, while Professor T. Rupert Jones has supplied some valuable notes and corrections. Nor should I omit to mention that the work owes not a little to the labours of the late Dr. P. M. Duncan, who revised the fourth edition of the ' Student's Elements,' to the late Messrs. Searles V. Wood and David Forbes, as well as to Mr. Robert Etheridge and Professor T. G. Bonney, who aided Lyell in the preparation of the work for a second edition. The size of the book of course precludes its being made an exhaustive treatise on geology, with full references to original memoirs ; nor dare I anticipate that all my fellow-teachers will coincide with me in judgment as to what should be included in and what it is best to omit from a work with the scope and limits of the present one ; yet I venture to hope that the modifications, rearrangements, and additions now introduced into the book have served to bring it up to date, and that teachers and students may alike find that it continues to be what Lyell made it — a convenient and trustworthy introduction to geological science.

JOHN W. JUDD. Kew : March 1896. Museum, and in many provincial museums. Specimens, rock sec tions, and microscopical prepara tions, &c, specially arranged to illustrate the different portions of this work, may be procured from Mr. F. H. Butler, 158 Brompton Eoad, London, S.W. Aa it is impossible to enable the reader to recognise minerals, rocks, and fossils by the aid of figures and verbal descriptions only, he will do well to refer to properly labelled specimens. Such may be seen in the British Museum of Natural History, the Jermyn Street PAGE CONTENTS

Part I Introductory Chapter

I GEOLOGY DEFINED — HISTORY OF THE DEVELOPMENT OF GEOLOGICAL SCIENCE Geology compared to History — Its relation to other Physical and Natural Sciences — Not to be confounded with Cosmogony — Opinions of Classical and Mediæval writers — Causes which have retarded the Progress of Geology ....... 1

Chapter II The Crust Of The Globe

What geologists mean by the earth's crust — Physical characters of the crust of the globe — Chemical composition of the solid crust and of its liquid and gaseous envelopes — Distribution of temperature in the earth's crust — Distribution of pressure in the earth's crust 1

Chapter IV Composition And Classification Of Aqueous Rocks Page

Chemical, mechanical, and organic deposits — Arenaceous rocks — Argillaceous rocks — Calcareous rocks — Other varieties of aqueous rocks — Phosphatic deposits — Ironstones — Gypsum — Bock salt — Carbonaceous deposits — Peat — Coal — Anthracite .... 23

Chapter V Structures Produced In Aqueous Rock-masses During Their Deposition

Forms of stratification — Original horizontality of strata— False-bedding or oblique lamination — Irregularities in the accumulation of strata— Thinning-out and alteration in the characters of strata — Ripple-marks, sun-cracks, footprints, tracks, trails, burrows, and worm-casts 34

Chapter VI Arrangement Of Fossils In Strata

— MARINE, FRESHWATER, AND TERRESTRIAL DEPOSITS Slow deposition of strata proved by fossils — Rocks formed of the remains of organisms — Diatomaceous deposits — Bog-iron ore and lake-ores of Sweden — Importance of fossils as indicating the conditions under which strata were deposited — Deep-sea deposits — Radiolarian deposits, chalk and other limestones — Distinction of freshwater from marine formations — Genera of freshwater and land shells — Rules for recognising marine shells — Alternation of marine and freshwater deposits — Terrestrial deposits and their fossils — Origin of coal and other carbonaceous rocks ... 43

Chapter VII Consolidation And Subsequent Alterations Of Strata And Petrification Of Organic

REMAINS Consolidation of strata — Concretionary structures — Jointed structure — Mineralisation -of organic remains — Formation of casts — Won- CONTENTS [ 11 PAGE derful preservation of the internal structures of fossil organisms — Petrifactions and incrustations — Pseudo-fossils .... 64

Chapter VIII Elevation Of Strata Above The Sea

— HORIZONTAL AND INCLINED STRATIFICATION — FAULTING 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 freshwater beds and old land surfaces — Vertical, inclined, and folded strata — Anticlinal and synclinal curves — 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 — Overlap — Dip-slopes and escarpments— Outliers and inliers 75

Chapter IX Denudation And Its Effects

Denudation defined — Its amount more than equal to the entire mass of stratified deposits in the earth's crust — Subaerial 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 102

Chapter X Joint Action Of Denudation, Upheaval, And Subsidence In Remodelling The

EARTH'S CRUST How we obtain an insight, at the surface, "of tKe 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 subaerial denudation — Antagonism of subterranean 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 — Supposed permanence of continental and oceanic areas CONTENTS PAGE Section II. — Chronological Classification of Aqueous Rocks

Chapter XI Principles On Which The Classification Of Sedimentary Rocks Is Based

Aqueous, Volcanic, Plutonic, and Metamorphic rocks considered chronologically — Terms Primary, Secondary, and Tertiary; Palæozoic, Mesozoic, and Cainozoic explained — On the different ages of aqueous rocks — Principal tests of relative age ; superposition, mineral characters, fossils, and included fragments — Faunas and floras determined by conditions, geographical position, and geological age — William Smith's classification of British deposits by their organic remains — Danger of extending the palæontological method over wide areas — Homotaxy — Combination of physical and palæontological methods — Classification of tertiary strata — Tabular view of fossiliferous strata 126 THE CAINOZOIC (TERTIARY) ERA

Chapter XII The Pleistocene Period With The Glacial Episode

Use of the terms ' pleistocene,' ' recent,' and ' human ' periods — Mollusca of the Pleistocene period — Mammalia of the Pleistocene period — Shorter duration of mammalian as compared with molluscan species — Geographical distribution of mammalia in Pleistocene times similar to that at present day — Remains of man — Flint implements — Shell-mounds — Cavern-deposits — Valley gravels — Highand low-level gravels — Brick-earth — Loess — Lacustrine deposits — Estuarine deposits — Marine deposits — Subdivisions of the Pleistocene period — Pre-glacial — The Glacial period — Origin of Boulder clay — Glacial lakes and other phenomena of glaciated districts — Post-glacial, Pluvial and Champlain periods — Palæolithic and Neolithic — Copper, Bronze, and Iron Ages 147

Chapter XIII The Newer Tertiary Strata

(NEOGENE OR NEOCENE) Use of the terms Miocene and Pliocene, Neogene and Neocene — Mollusca of the Newer-Tertiary Strata — Mammalia of the Newer CONTENTS PAQE 171 19J 219 Tertiaries — The Newer Tertiary Flora — British Newer and Older Pliocene Strata — Forest-bed of Cromer — Chillesford and Aldeby beds — Red Crag — White or ' Coralline ' Crag — Older Pliocene deposits of the North Downs and of St. Erth — Relation of the Fauna of the Crag to that of the present day — Proofs of denuda tion between the periods of deposition of the British Older and Newer Tertiaries

Chapter XIV The Older Tertiary

(EOGENE OR EOCENE) Geographical Distribution of the Older-Tertiary Strata — The London and Hampshire basins — Foraminifera, corals, echinodermata, and crustaceans of the Older Tertiaries— The Older Tertiary Mollusca — The fish, reptiles, birds, and mammals of the period — The Older Tertiary flora. The British Older- Tertiary Strata. Hempstead Beds — The Bembridge Series — The Headon Series — The Brockenhurst Marine Group — The Barton Sands and Clay — The Bracklesham Series — The Bournemouth Beds — The Plant-beds of Bovey Tracey and Mull — The London Clay — The Oldhaven beds and Woolwich and Reading Series — The Thanet Sands

Chapter XV Foreign Deposits Which Are Homotaxial With The Cainozoic Of The

BRITISH ISLES Tertiaries of France and Belgium — Montian — Argile plastique — Calcaire grossier — Gypsum of Montmartre — Mammals of Oligocene of Northern and Central France — Faluns of Touraine and Bordeaux — Pliocene of Northern France and Belgium — Tertiaries of Central Europe — Lower Brown Coal and Amber deposits — Mayence Basin — Pliocene of Eppelsheim — Tertiaries of Alps and Switzerland — Flysch and Nummulitic formations — Lower, Middle, and Upper Molasse — Plants and insects of Oeningen — Tertiaries of Italy — Oligocene and Miocene — Subapennine strata — Newer Pliocene of Sicily and the Val d'Arno — Tertiaries of Eastern Europe — Oligocene of Croatia — Miocene (Leithakalk and Sarmatian) of Vienna basin — Pliocene (Congeria) strata — Tertiaries of India — Sind and Sivrilik strata — Post-pliocene deposits of Northern Europe and the Alps — Scandinavia and Russia — Central Europe — Alps and Jura — Older and Newer Palæolithic periods — Lake-dwellings — Post-pliocene of India, New Zealand, and Australia — Tertiaries of North America — Eocene and Neocene of Eastern States — Mammals and Plants of Tertiaries of the Western Territories — American Post-pliocene deposits — Glacial and Champlain periods — Tertiary Zones in Europe CONTENTS PA0E 248 275 THE MESOZOIC (SECONDARY) ERA

Chapter XVI The Cretaceous System

Lapse of time between Eocene and Cretaceous Periods — Classification of Cretaceous strata— Foraminifera, Sponges, Corals, Bryozoa, and Mollusca of the Cretaceous Period — Terrestrial Floras of the Cretaceous— Reptiles, Birds, and Mammals of the Cretaceous — Chalk and Flint— Zones of the Chalk with their fossils— Chalk Marl — Upper Greensand — Gault — Upper Neocomian — Atherfield Clay — Middle Neocomian— Tealby Series — Lower Neocomian — Speeton Clay — Spilsby Sands — The Wealden and Hastings Sands — Punfield bedB

Chapter XVII The Jurassic System

Classification of Jurassic strata — Foraminifera, Sponges, Corals, Echinodermata, Brachiopoda — Lamellibranchiata, Gastropoda, and Cephalopoda of Jurassic rocks — Fishes, reptiles, birds, and mammals of the Jurassic rocks — Terrestrial Flora of the Jurassic period — Purbeck strata — Purbeck mammals — Dirt-beds — Portlandian — Kimeridge Clay — Coralline Oolite — Oxford Clay — Cornbrash — Forest Marble — Great Oolite — Stonesfield Slate with its Mammalia — Inferior Oolite — Upper Lias sand and clay — Marlstone and Middle Lias — Lower Lias — Rhætic beds

Chapter XVIII The Triassic System

Subdivisions of the Trias in England— Corals, Echinodermata, Brachiopoda, Lamellibranchiata, Gastropoda, and Cephalopoda of the Trias — Fish, Amphibians, and Reptiles — Terrestrial Flora of the Trias — Triassic Mammalia — The Keuper and its Reptilia — The Dolomitic Conglomerate — Elgin Sandstones — The Bunter Formation of Red Sandstones and Clays — Rock-salt, Gypsum, &c CONTENTS

Chapter XIX Foreign Deposits Which Are Homotaxial With The Mesozoic Strata Of

THE BRITISH ISLES TAGE Secondary Strata of Central Europe — Keuper, Muschelkalk, and Bunter — The Black, Brown, and White Jura — Planer and Quader Beds — Chalk of Maestricht and Faxoe — Freshwater Strata — Wealden of Hanover — Strata of Aix-la-Chapelle — Secondary Strata of the Alpine Regions — Hallstadt and St. Cassian Beds — Alpine Jurassic, Tithonian, and Neocomian — Hippurite Limestones — Secondary Strata of Russia, India, and South Africa — Secondary Strata of North America — Newark Formation — Strata of the Eastern States and of the Western Territories . . . 323 THE NEWER PALÆOZOIC ERA

Chapter XX The Permian System

Subdivisions of the Permian — Permian Marine Fauna of India, Texas, Russia, &c. — Foraminifera — Corals — Brachiopoda — Ammonites and other Cephalopoda — Arthropods — Fish, Amphibians, and Reptiles — Terrestrial Flora — Relations with Carboniferous and Trias respectively — Upper Permian — Magnesian Limestone and Marlslate, with their Fossils — Lower Permian, with its breccias ............ 338

Chapter XXI The Carboniferous System

Succession of Strata in the Carboniferous System — Carboniferous Foraminifera and Corals, Echinodermata, Braohiopoda, Lamellibranchiata, Gastropoda and Cephalopoda of the Period — Carboniferous Fishes and Amphibians — The Carboniferous Flora — Peculiarity in Mode of Growth of the Cryptogams of the Period — Ferns, Calamites, Lepidodendra, &c. — Land-shells and Insects of the Carboniferous Period— Carboniferous Strata of Britain — Coal-measures — Millstone Grit — Carboniferous Limestone and Yoredale Series — Tuedian Series — Scottish Carboniferous — Calciferous Sandstone Series — Mode of Formation of the Carboniferous Strata — Coal-seams, Ironstones, &c. — Marine and Freshwater Strata of Carboniferous CONTENTS PAOK 374

Chapter XXII The Devonian System

Relations of the Devonian — Devonian Corals, Brachiopoda, Cephalopoda, and Trilobites — The Devonian Fish and their Relationships to Living Forms — The Devonian Flora and its Relation to that of the Carboniferous — Devonian Strata of Devon and Cornwall — Upper, Middle, and Lower Devonian — Old Red Sandstone — Relations to Devonian — Proof of Freshwater Origin — Old Red Sandstone of Scotland, Lower, Middle, and Upper — Old Red Sandstone of England and Wales — Old Red Sandstone of Ireland

Chapter XXIII Foreign Deposits Which Are Homotaxial With The Newer

PALÆOZOIC STRATA OF THE BRITISH ISLES The Devonian rocks of the Eifel — of the Ardennes, and Brittany — ■ of the Carinthian Alps, the Iberian peninsula and Russia — Carboniferous strata of France, Germany, and Russia — Permian strata of Central Germany, the Alps, and the Ural Mountains — Devonian strata of the United States, Canada, and the Arctic Regions — Carboniferous strata of the United States — Permian strata of Texas and Nebraska — Devonian, Carboniferous, and Permian of India and Australia 391 THE OLDER PALÆOZOIC ERA

Chapter XXIV The Silurian System

Classification of Silurian rocks — Characteristics of the Marine Flora and Fauna of the Silurian — Graptolites — Corals — Echinodermata — Brachiopoda — Gastropoda — Cephalopoda — Fish — British representatives — Shropshire — North Wales — Lake District — Scotland — Details of strata in the typical area — Upper Ludlow — Lower Ludlow — Aymestry Limestone — Oldest known fossil fish Wenlock Limestone — Wenlock Shale — Woolhope Limestone Tarannon Shales and Denbighshire Grits — Upper and Lower Llandovery rocks — May-Hill beds CONTENTS 17

Chapter XXV The Ordovician System Tage

Classification of Ordovician strata — Characteristics of the marine Fauna — Foraminifera — Graptolites — Echinodermata — Brachiopoda — Gastropoda — Cephalopoda — Worms — Trilobites and their organisation — Bala or Caradoc strata — Llandeilo beds — Arenig beds or Stiper-stones — Ordovician strata of the Lake District— Ordovician strata of Scotland 410

Chapter XXVI The Cambrian System

Divisions of the Cambrian System — Cambrian Flora and Fauna — Sponges — Graptolites — Echinodermata — Brachiopoda — Mollusca — Annelida — Trilobita — The oldest known fossils of the Lower Cambrian Period — Upper Cambrian, Tremadoc slates and Lingula Flags — Middle Cambrian, Menevian beds, Harlech grits, and Llanberis slates — Lower Cambrian, Comley Sandstone, Cambrian of Scotland, Durness Limestone, Girvan Limestone — ' Fucoid ' and Olenellus beds ... 419

Chapter XXVII Foreign Deposits Which Are Homotaxial With The Older

PALÆOZOIC STRATA OF THE BRITISH ISLES Older Palæozoic strata less altered than the British — Basin of Bohemia — ' Primordial ' strata of Barrande — Stages D, E, F — Older Palæozoic strata of Scandinavia — Olenellus beds — Alum Shales — Limestones and Schists — Russia and other parts of Europe — North America — Geographical distribution of life forms in Cambrian times — Table showing equivalence of strata in different areas 429

Chapter XXVIII Sedimentary Rocks Of Pre-cambrian Age

Existence of stratified and other Rock-masses underlying the Older Palæozoic Deposits — Rocks of both Igneous and Aqueous Origin — Obscure Traces of Fossils — Thickness and Extent of Pre- Cambrian Rocks — Pre-Cambrian strata of the British Isles — Pebidian — Arvonian — Dimetian — Fundamental Gneiss, or Lewia CONTENTS PAGE 432 109 455 sian — Caledonian, or Dalradian — Malvernian — Monian — Urico nian — Longmyndian — The Torridon Sandstone, or Torridonian — Pre-Cambrian of Europe and North America — Huronian — Laurentian, Upper and Lower — Algonkian and Archæan — Pre- Cambrian of India — Traces of Fossils in pre-Cambrian Rocks

Chapter XXIX General Review Of The Succession And Characters Of The Sedimentary

ROCKS Fossils not found uniformly distributed in Sedimentary Formations — Imperfection of our Knowledge of Freshwater and Terrestrial Conditions during past Geological Times — Existence of Organisms before Cambrian Times — Dlustrations of the great Lnperfection of the Geological Record — ' Time-ratios ' of the Geological Eras — Date of Appearance of different Forms of Life as modified by new Discoveries of Fossils — General Order in which Life-forms have appeared upon the Earth — Groups of Animals and Plants which have predominated in successive Periods — Synthetic Types — Specialised Types — Persistent Types — Summary of Palæontological History — Table of Fossiliferous Sedimentary Formations PAET III VOLCANIC ROCKS

Chapter XXX Volcanic Rocks, Their Nature And

COMPbSITION Relation of volcanic Rocks to the sedimentary and hypogene Rocks — Nature of Action taking place at Volcanic vents — Lavas and their Varieties — Fragmental materials ejected from Volcanoes — Scoriæ, lapilli, dust, pumice, bombs — Formation of volcanic Tuffs Alteration of volcanic Rocks by solfataric and atmospheric agencies — Chemical composition of lavas — Acid, intermediate and basic lavas — Rhyolites and Soda-rhyolites — Andesites, Trachytes Phonolites, and Tephrites — Alteration of Andesites — Propylites and Porphyrites — Basalt and Melaphyres — Tachylytes and Variolites — Basaltic and Palagonite Tuffs CONTENTS

Chapter XXXI Origin And Structure Of Volcanic Rock-masses Page

Explosive and effusive action of Volcanoes — Origin of Volcanic Cones — Internal structure of Volcanic Cones — Origin of Volcanic Craters — Fofmation of Volcanic Dykes — Varieties of Volcanic Dykes — Alteration of Rocks on the sides of Volcanic Dykes — Contact Metamorphism — Alteration of Sandstone, Shale, Limestone, and Coal — Interbedded and contemporaneous Volcanic Rocks contrasted with intrusive or subsequent masses — Columnar and globular structures in Lavas 466

Chapter XXXII Principles On Which The Chronological Classification Of Volcanic Rocks Is

BASED Variations of mineral character in the volcanic rocks of different periods — Not essential, but due to alteration — Age of lava flows and intrusions — Tests to be applied to determine relative age of volcanic masses — Sources of error in drawing inferences — Great value of fossils when found — Test by included fragments — Order in which volcanic rocks have been erupted — Views of Bunsen, Duroeher, Richthofen, and later authors 48S

Chapter XXXIII Volcanic Rocks Of Cainozoic Age

The latest exhibitions of volcanic energy in the British Islands — The thermal springs of Bath, t_c. — Tertiary volcanoes of the west of Scotland and the north of Ireland — First period of eruption — Second period of eruption — Third period of eruption — Tertiary volcanic rocks of other parts of Europe — Vesuvius — Auvergne — Newer Pliocene volcanoes of Italy — Older Pliocene volcanoes of Italy and the Eifel — Oligocene and Miocene volcanoes of Auvergne and the Eifel — Eocene volcanic rocks of Monte Bolca — Tertiary volcanic rocks of the Atlantic Islands — of India — of the United States and Australia 488

Chapter XXXIV Volcanic Rocks Of The Mesozoic

PALÆOZOIC, AND ARCHÆAN ERAS Absence of evidence of volcanic action in Cretaceous and Jurassic times in the British Isles and Western Europe — Triassic Volcanoes of Devonshire — Permian Volcanoes of Scotland — Volcanoes of the Carboniferous Period — Buried trees of Arran — Volcanoes of the Old Red Sandstone and Devonian Period — Volcanoes of the CONTENTS PAGH Silurian, Ordovician, and Cambrian Periods — Pre-Cambrian Volcanoes — Pre-Tertiary Volcanoes of other parts of the globe — Cretaceous and Jurassic volcanic rocks of Greece — Newer and Older Palæozoic Volcanoes of Central Europe — Pre-Cambrian volcanic rocks of Canada 502

Part IV Plutonic Rocks Chapter XXXV Plutonic Rocks, Their Nature And Composition

Analogy of the plutonic Rocks to those of volcanic origin — Proofs of the deep-seated origin of Plutonic Rocks — Chemical composition of the different classes of Plutonic Rocks — Changes which they undergo — Liquid cavities in the crystals of Plutonic Rocks — Order in which the several minerals crystallise in Plutonic Rocks — Granite and its varieties — Syenites, &c. — Diorites, &c. — Nepheline syenites and Theralites — Gabbro and its varieties — Ultra-acid Rocks — Ultra-basic Rocks — Peridotites — Pyroxenites — Amphibolites — Relations of the Ultra-basic Rocks to Meteorites 509

Chapter XXXVI Structure And Origin Of Plutonic Rock-masses

: THEIR RELATIONS TO ROCKS OF VOLCANIC AND SEDIMENTARY ORIGIN Plutonic Rocks can only be exposed at the earth's surface by denudation — Latest formed Rocks of this class never seen at the surface — Relations of Plutonic masses to Volcanic extrusions — Examples from the Western Isles of Scotland and Antrim — Examples in other areas — Features exhibited by Plutonic Rock-masses — Forms produced by weathering — Veins and Dykes — Segregation Veins — Result of segregative action in Plutonic Rock-masses — Inclusions and Veins — Differentiation in Igneous Magmas and its results 520

Chapter XXXVII Plutonic Rocks Belonging To Different Geological Periods

Plutonic Rocks were formed during the whole of the geological periods — Those of the most recent period seldom exposed at th« CONTENTS 21 TAGE surface by denudation — Test of the geological age of Plutonic Rock-masses — Relative position — Intrusion and Alteration — Mineral composition— Included fragments— Tertiary Plutonic Rocks of Western Scotland, North-East Ireland, Elba, &c— Difficulty of determining the age of Plutonic Rock-masses in Mountain chains — Plutonic Rocks of the Cretaceous — the Jurassic — the Carboniferous — the Ordovician — and Pre-Cambrian Periods 528

Part V Metamorphic Rocks Chapter Xxxviii Metamorphic Rocks, Their Nature And Origin

Contact Metamorphism and Regional Metamorphism — Thermo-metamorphism and Hydrothermal action — Dynamo -metamorphism — Different results of Metamorphic action — Researches of Daubrtje and others on Thermo-metamorphic and Hydrothermal action — Dynamo-metamorphic action and its results — Slaty cleavage — Its nature and origin — Investigations of Phillips, Sharpe, Sorby, &c. — Experimental proofs of origin of slaty cleavage — Foliation, its nature and origin — Relations between Cleavage and Foliation — Experimental researches of Daubr6e, Spring, and others upon the action of pressure in producing Metamorphism .......... 537

Chapter XXXIX Contact Metamorphism And Regional Metamorphism

\ THE VARIETIES OF ROCKS RESULTING FROM THESE TWO KINDS OF ACTION Illustrations of the action of Contact Metamorphism — Distance to which Contact Metamorphism can be traced from the intrusive mass — Minerals produced by Contact Metamorphism — Chief types of Rocks produced by Contact Metamorphism — Andalusite, Kyanite, Sillimanite, Staurolite Rocks, &c. — Rocks produced by Regional Metamorphism, Quartzites, Metamorphic Limestones, and Dolomites, Slates, Phyllites, Schists, Gneisses, Granulites, Anthracites, &c CONTENTS PAGK 563

Chapter XL The Formation Of Mountain-chains

Various types of Mountain-chains— Majority of Mountain-chains belong to Appalachian type— Structure of the Scottish Highlands and similar denuded Mountain-chains — Mountain-forms due proximately to denudation — Sequence of events in Mountain-making— Geo-synclinals— Ge-anticlinals— Mountain sculpture

Chapter XLI Ore-deposits And Their Origin

Ore-deposits usually formed by Hypogene action — Classification of Ore-deposits — Origination of Metalliferous Veins in fissures — Different ages of the formation and infilling of Veins — Proofs of successive opening and refilling of Veins — Comb-structure in Veins — Irregularities in width of Veins — Chemical Deposition in Veins — Supposed relative ages of different metals . . . 568

Chapter XLII On The Different Ages Of Metamorphic Rocks, Mountain-chains, And Ore-deposits

How the age of Metamorphic Rocks is determined — Period of original formation — Period of Metamorphism — Disturbed condition of Metamorphic Rocks — Age of Rocks formed by Contactmetamorphism — Similarity of Rocks formed by Contact-metamorphism to those produced by Regional-metamorphism — Difficulty of determining age of Rocks formed by latter process — Metamorphic Rocks of the Alps — Supposed Tertiary age — Metamorphic Rocks of Mesozoic Age — Metamorphic Rocks of Newer Palæozoic Age — Metamorphic Rocks of Older Palæozoic Age — Metamorphic Rocks of Pre-Cambrian Age — Uniformity of characters in Metamorphic Rocks of all ages — Supposed parallelism of Mountain-chains formed during different periods — Mountain-chains of Tertiary, Mesozoic, Palæozoic and Archæan Ages — Ages of Ore-deposits — Supposed relative ages of different metals— rOrigin and age of Gold-deposits . . . ' , . CONTENTS 23

Part VI Conclusion Chapter XLIII Grounds For Accepting Uniformitarianism As The Basis

OF GEOLOGICAL REASONING PAGE Vastness of Geological Time — Proved by Physical and Palæontological evidence — Attempt to determine Time Ratios for the several geological periods — Attempts to measure geological periods in years — The doctrines of Catastrophism, Evolution, and Uniformitarianism — Evidences in favour of Uniformitarianism during the periods covered by the geological history — The Science of Geology limited to the study of the crust of the Globe — Bearing of speculations concerning the earth's interior on the Science of Geology — The Geological Record may only cover a small portion of the history of the Globe during past times . . 589

Appendix

A. The common Rock-forming Minerals 601

APPENDIX.

B. Classification of Plants, living and fossil 607

APPENDIX.

C. Classification of Animals, living and fossil 608 INDEX Paj Errata ;e 154, line 11 from bottom,/or extent, read extinct 1D3, in description of fig. 182, last line, for outlines, read outliers 257, line 9, for Chalk, read Upper Chalk 262, „ 3, for A lower, read The upper part of this 277, „ 20, for Thecosimlia, read Thecosmilia 277, „ bottom, for Gastriopoda, read Gastropoda 318, „ 6, dele and jaws without teeth but 326, ,, 11, for Oxynotieras, read Oxynoticeras 329, „ 19 for of, read or 334, „ 6,/or 450, read 451 334, „ 26, col. 2, for Cretaceans, read Cretaceous 376, „ 5, for a. Ventral valve, b. Inner side of dorsal valve, read a. Corallum. b. Operculum 386, „ 5, dele Morte slates (without fossils). (Dr. Hicks has recently detected fossils in these beds which appear to show that the strata are of Silurian age faulted up in the midst of the Devonian.) 423, » 1,/or Dicellocephalus, read Dikelocephalus 536, „ 4 from bottom, /or Tirkel, read Zirkel 586, „ 28, for a Tertiary formation, read of Tertiary age THE STUDENT'S LYELL

Part I Introductory Chapter

I GEOLOGY DEFINED — HISTORY OF THE DEVELOPMENT OF GEOLOGICAL SCIENCE Geology compared to History — Its relation to other Physical and Natural Sciences — Not to be confounded with Cosmogony — Opinions of Classical and Mediæval writers— --Causes which have retarded the Progress of Geology. Geology is the science which investigates the successive changes that have taken place in the inorganic and organic kingdoms of nature ; it inquires into the causes of these changes, and the influence which they have exerted in modifying the surface and external structure of our planet. By these researches into the state of the earth and its inhabitants at former periods we acquire a more perfect knowledge of its present condition, and more comprehensive views concerning the laws noiv governing its animate and inanimate productions.

When we study history, we obtain a more profound insight into human nature, by instituting a comparison between the present and former states of society. We trace the long series of events which have gradually led to the actual posture of affairs, and, by connecting effects with their causes, we are enabled to classify and retain in the memory a multitude of complicated relations — the various peculiarities of national character, the different degrees of moral and intellectual refine ment, and numerous other circumstances — which, without historical associations, would be uninteresting or imperfectly understood. As the present condition of nations is the result of B INTRODUCTORY [CH. I. many antecedent changes — some extremely remote and others recent, some gradual, others sudden and violent — so the state of the natural world is the result of a long succession of events, and, if we would enlarge our experience of the present economy of nature, we must investigate the effects of her operations in former epochs.