A Manual of Elementary Geology. ... Third and entirely revised edition

Front matter

Prom a PainUn. by James nail, Esq. ED^raved by S. WilUama. STRATA OP P.SD SANDSTONE. SLIGHTLY INCLINED. RESTING ON VERTICAL SCHIST. AT THE SICCAR POINT, BERWICKSHIRE. To illc9:k_te .mco-fo__ablu Strati, ication. See page ty. " The mind seemed to grow giddy by boking so far into the abyss of time ; and while we listened with earnestness and admiration to the philosopher who was now unfolding to us the order and series of these wonderful events, we became sensible how much farther reason m-xy sometimes go titan imagination can Venture to follow." — P___»J_UR, -T.^i.tiltyot Hutton. A MANUAL OF ELEMENTARY GEOLOGY OK, THE ANCIENT CHANGES OF THE EARTH AND ITS INHABITANTS AS ILLUSTKATED BY GEOLOGICAL MONUMENTS. BY SIR CHARLES LYELL, M.A. F.R.S. PRESIDENT OP THE GEOLOGICAL SOCIETY OP LONDON ; AUTHOR OF " PRINCIPLES OF GEOLOGY," " TRAVELS IN NORTH AMERICA,'' " A SECOND VISIT TO THE UNITED STATES," etc. etc.

" It is a philosophy which never rests — its law is progress : a point which yesterday was invisible is its goal to-day, and will be its starting post to-morrow." Edinburgh Review, No. 132. p. 83. July 1837. THIRD AND ENTIRELY REVISED EDITION. Illustrate!, tenth mart tijan ffibz IjunaTc-J OTfoottnits.. LONDON: JOHN MURRAY, ALBEMARLE STREET. 1851. London : Spottiswoodes and Sniw, New -street-Square.

Preface

. This treatise is not an epitome of the " Principles of Geology," nor intended as introductory to that work. I find it necessary to state this at once, and to explain the different ground occupied by the two publications, because much confusion has arisen on the subject. The first five editions of the " Principles " comprised a 4th book, in which some account was given of systematic geology, and in which the principal rocks composing the earth's crust and their organic remains were described. In subsequent editions this book was omitted, it having been expanded, in 1838, into a separate treatise called the " Elements of Geology," first re-edited in 1842 and now again recast and enlarged. Although the subjects of both treatises relate to geology, as their titles imply, their scope is very different, the " Principles " containing a view of the modern changes of the earth and its inhabitants, while the " Manual " relates to the monuments of ancient changes.

In separating the one from the other, I have endeavoured to render each complete in itself, and independent ; but if asked by a student which he should read first, I would recommend him to begin with the " Principles," as he may then proceed from the known to the unknown, and be provided before hand with a key for interpreting the ancient phenomena whether of the organic or inorganic world, by reference to changes now in progress. Owing to the former incorporation of the two subjects in one work, and the supposed identity of their subject matter, it may be useful to give here a brief abstract of the contents of the " Principles," for the sake of comparison. Abstract of the " Principles of Geology," Eighth Edition. Book I. 1. Historical sketch of the early progress of geology, chaps, i. to iv. 2. Circumstances which combined to make the first cultivators of the science regard the former course of nature as different from the A

PREFACE.

. VI present, and the former changes of the earth's surface as the effects of agents different in kind and degree from those now acting, chap. v. 3. Whether the former variations in climate established by geology are explicable by reference to existing causes, chaps, vi. to viii. 4. Theory of the progressive development of organic life in former ages, and the introduction of man into the earth, chap. ix. 5. Supposed former intensity of aqueous and igneous causes considered, chaps, x. and xi. 6. How far the older rocks differ in texture from those now forming, chap. xii. 7. Supposed alternate periods of repose and disorder, chap. xiii. Book II. CHANGES MOW IN PROGRESS IN THE INORGANIC WORLD, 8. Aqueous causes now in action : Floods — Rivers — Carrying power of ice — Springs and their deposits — Deltas — Waste of cliffs and strata produced by marine currents : chaps, xiv. to xxii. 9.

Permanent effects of igneous causes now in operation : Active voleanos and earthquakes — their effects and causes : chaps, xxiii. to xxxiii. Book III. CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS. 10. Doctrine of the transmutation of species controverted, chaps, xxxiv. and xxxv. 11. Whether species have a real existence in nature, chaps, xxxvi. and xxxvii. 12. Laws which regulate the geographical distribution of species, chaps. xxxviii. to xl. 13. Creation and extinction of species, chaps, xli. to xliv. 14. Imbedding of organic bodies, including the remains of man and his works, in strata now forming, chaps, xlv. to 1. 15. Formation of coral reefs, chap. li. It will be seen on comparing this analysis of the contents of the " Principles " with the headings of the chapters in the next nine pages which follow, that the two treatises have but little in common; or, to repeat what I have said in the Preface to the 8th edition of the "Principles," they have the same kind of con nection which Chemistry bears to Natural Philosophy, each being subsidiary to the other, and yet admitting of being con sidered as different departments of science.* Charles Lyell. 11.

Harley Street, London, January 1. 1851. * As it is impossible to enable the reader to recognise rocks and minerals at sight by aid of verbal descriptions or figures, he will do well to obtain a well-arranged collection of specimens, such as may be procured from Mr. Tennant (149. Strand), teacher of Mineralogy at King's College, London. ' CONTENTS.

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 - Page 1 CHAPTER H. AQUEOUS ROCKS — THEIR COMPOSITION AND FORMS OF STRATIFICATION. Mineral composition of strata— Arenaceous rocks — Argillaceous — Calcareous — Gypsum — Forms of stratification — Original horizontally — thinning out — Diagonal arrangement — Ripple mark - - - - -10 CHAPTER IH. ARRANGEMENT OF FOSSILS IN STRATA FRESHWATER 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 and semi-opal formed of infusoria — Chalk derived principally from organic bodies — Distinction of freshwater from marine formations — Genera of freshwater and land shells — Rules for recognizing marine testacea — Gyrogonite and chara — Freshwater fishes — Alternation of marine and freshwater 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 — Concretionaiy nodules — Consolidating effects of pressure — Mineralization of organic remains — Impressions and casts how formed — Fossil wood — Giippert's experiments — Precipitation of stony matter most rapid where putrefaction is going on — Source of lime in solution — Silex derived from decomposition of felspar — Proofs of the lapidification of some fossils soon after burial, of others when much decayed - - - - - 33 A CONTENTS.

CHAPTER V. ELEVATION OF STRATA ABOVE TIIE

6EA ■ — 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 — Upheaval of extensive masses of horizontal strata — Inclined and vertical stratification — Anticlinal and synclinal lines — Bent strata in east of Scotland — Theory of folding by lateral movement — Creeps — Dip and strike — Structure of the Jura — Various forms of outcrop — Rocks broken by flexure— Inverted position of disturbed strata — Unconformable stratification — Hutton and Playfair on the same — Fractures of strata — Polished surfaces — Faults — Appearance of repeated alternations produced by them — Origin of great faults ... Page 44

CHAPTER VI. DENUDATION.

Denudation defined — Its amount equal to the entire mass of stratified deposits in the earth's crust — Horizontal sandstone denuded in Ross-shire — Levelled surface of countries in which great faults occur — Coalbrook Dale — Denuding power of the ocean during the emergence of land — Origin of valleys — Obliteration of seacliffs — Inland sea-cliffs and terraces in the Morea and Sicily — Limestone pillars at St. Mihiel, in France — in Canada — in the Bermudas - - - 66 CHAPTER VH. ALLUVIUM. Alluvium described — Dae to complicated causes — Of various ages, as shown in Auvergne — How distinguished from rocks in situ — Riverterraces — Parallel roads of Glen Roy — Various theories respecting their origin - - 79 CHAPTER VHI. CHRONOLOGICAL CLASSIFICATION OF ROCKS. Aqueous, plutonic, volcanic, and metamorphic rocks, considered chronologically — Lehman's division into primitive and secondary — Werner's addition of a transition class — Neptunian theory — Hutton on igneous origin of granite — How the name of primary was still retained for granite — The term " transition," why faulty — The adherence to the old chronological nomenclature retarded the progress of geology — New hypothesis invented to reconcile the igneous origin of granite to the notion of its high antiquity — Explanation of the chronological nomenclature adopted in this work, so far as regards primary, secondary, and tertiary periods - - - - - - - -89

CHAPTER IX. ON THE DIFFERENT AGES OF THE AQUEOUS ROCKS.

On the 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 — Principal groups of strata in western Europe - - - - . - CONTENTS. IX

CHAPTER X. CLASSIFICATION OF TERTIARY

FOR3LVTIONS. — POST-PLIOCENE GROUP. General principles of classification of tertiary strata — Detached formations scattered over Emope — Strata of Paris and London — More modern groups Peculiar difficulties in determining the chronology of tertiary formations — Increasing proportion of living species of shells in strata of newer origin — Terms Eocene, Miocene, and Pliocene — Post-Pliocene strata — Recent or human period — Older Post-Pliocene formations of Naples, Uddevalla, and Norway — Ancient upraised delta of the Mississippi — Loess of the Rhine - - -Page 104

CHAPTER XI. NEWER PLIOCENE PERIOD.

BOULDER FORMATION. Drift of Scandinavia, northern Germany, and Russia — Its northern origin — Not all of the same age — Fundamental rocks polished, grooved, and scratched — Action of glaciers and icebergs — Fossil shells of glacial period — Drift of eastern Norfolk — Associated freshwater deposit — Bent and folded strata lying on undisturbed beds — Shells on Moel Tryfane — Ancient glaciers of North Wales — Irish drift. 121

CHAPTER XII.

boulder formation — continued. Difficulty of interpreting the phenomena of drift before the glacial hypothesis was adopted — Effects of intense cold in augmenting the quantity of alluvium — Analogy of erratics and scored rocks in North America and Europe — Bayfield on shells in drift of Canada — Great subsidence and re-elevation of laud from the sea, required to account for glacial appearances — Why organic remains so rare in northern drift — Mastodon giganteus in United States — Many shells and some quadrupeds survived the glacial cold — Alps an independent centre of dispersion of erratics — Alpine blocks on the Jura — Recent transportation of erratics from the Andes to Chiloe — Meteorite in Asiatic drift - - 131 CHAPTER XIH. NEWER PLIOCENE STRATA AND CAVERN DEPOSITS. Chronological classification of Pleistocene formations, why difficult — Freshwater deposits in valley of Thames — In Norfolk cliffs — In Patagonia — Comparative longevity of species in the mammalia and testacea — Fluvio-marine crag of Norwich — Newer Pliocene strata of Sicily — Limestone of great thickness and elevation — Alternation of marine and volcanic formations — Proofs of slow accumulation — Great geographical changes in Sicily since the living fauna and flora began to exist — Osseous breccias and cavern deposits — Sicily — Kirkdale — Origin of stalactite — Australian cave-breccias — Geographical relationship of the provinces of living vertebrata and those of the fossil species of the Pliocene periods — Extinct struthious birds of New Zealand — Teeth of fossil quadrupeds. 146

CHAPTER XIV. OLDER PLIOCENE AND MIOCENE FORMATIONS.

Strata of Suffolk termed Red and Coralline crag — Fossils, and proportion of recent species — Depth of sea and climate — Reference of Suffolk crag to the older Pliocene period — Migration of many species of shells southwards during the glacial period — Fossil whales — Subapennine beds — Asti, Sienna, Rome — Miocene formations — Faluns of Touraine — Depth of sea and littoral character of fauna — Tropical climate implied by the testacea — Proportion of recent species of CONTENTS. X shells — Faluns more ancient than the Suffolk crag — Miocene strata of Bordeaux and Piedmont — Molasse of Switzerland — Tertiary strata of Lisbon — Older Pliocene and Miocene formations in the United States — Scwalik Hills in India. Page 161

CHAPTER XV. UPPER EOCENE FORMATIONS.

Eocene areas in England and France — Tabular view of French Eocene strata — Upper Eocene group of the Paris basin — Same beds in Belgium and at Berlin — Mayence tertiary strata — Freshwater upper Eoceno of Central France — Series of geographical changes since the land emerged in Auvergne — Mineral character an uncertain test of age — Marls containing Cypris — Oolite of Eocene period — Indusial limestone and its origin — Fossil mammalia of the upper Eocene strata in Auvergne — Freshwater strata of the Cantal, calcareous and siliceous — Its resemblance to chalk — Proofs of gradual deposition of strata - - 174

CHAPTER XVI.

Eocene formations — continued. Subdivisions of the Eocene group in the Paris basin — Gypseous series — Extinct quadrupeds — Impulse given to geology by Cuvicr's osteological discoveries — Shelly sands called sables moyens — Calcaire grossier — Miliolitcs — Calcaire siliceux — Lower Eocene in France — Lits coquilliers — Sands and plastic clay — English Eocene strata — Freshwater and fluvio-marine beds — Barton beds — Bagshot and Bracklesham division — Large ophidians and saurians — Lower Eocene and London Clay proper — Fossil plants and shells — Strata of Kyson in Suffolk — Fossil monkey and opossum — Mottled clays and sands below London Clay — Nummulitic formation of Alps and Pyrenees — Its wide geographical extent — Eocene strata in the United States — Section at Claiborne, Alabama — Colossal cetacean — Orbitoid limestone — Burr stone ... 190

CHAPTER XVII. CRETACEOUS GROUP.

Divisions of the cretaceous series in North -Western Europe — Upper cretaceous strata — Maestricht beds — Chalk of Faxoe — White chalk — Characteristic fossils — Extinct cephalopoda — Sponges and corals of the chalk — Signs of open and deep sea — Wide area of white chalk — Its origin from corals and shells — Single pebbles in chalk — Siliceous sandstone in Germany contemporaneous with white chalk — Upper greensand and gault — Lower cretaceous strata — Atherfield section, Isle of Wight — Chalk of South of Europe — Hippurite limestone — Cretaceous Flora — Chalk of United States - - . . -209 CHAPTER XVIH. WEALDEN GROUP. The Wealden divisible into Weald Clay, Hastings Sand, and Purbeck Beds— Intercalated between two marine formations — Weald clay and Cypris-bearing strata — Iguanodon — Hastings sands — Fossil fish — Strata formed in shallow water — Brackish-water beds — Upper, middle, and lower Purbeck Alternations of brackish water, freshwater, and land — Dirt-bed, or ancient soil Distinct species of fossils in each subdivision of the Wealden — Lapse of time implied Plants and insects of Wealden — Geographical extent of Wealden Its relation to the cretaceous and oolitic periods — Movements in the earth's crust to which it owed its origin and submergence ----.. CONTENTS. XI

CHAPTER XIX. DENUDATION OF THE CHALK AND WEALDEN.

Physical geography of certain districts composed of Cretaceous and Wealden strata — Lines of inland chalk-cliffs on the Seine in Normandy — Outstanding pillars and needles of chalk — Denudation of the chalk and Wealden in Surrey, Kent, and Sussex — Chalk once continuous from the North to the South Downs — Anticlinal axis and parallel ridges — Longitudinal and transverse valleys — Chalk escarpments — Rise and denudation of the strata gradual — Ridges formed by harder, valleys by softer beds — Why no alluvium, or wreck of the chalk, in the central district of the Weald — At what periods the Weald valley was denuded — Land has most prevailed where denudation has been greatest — Elephant bed, Brighton -------- Page 238

CHAPTER XX. OOLITE AND LIAS.

Subdivisions of the Oolitic or Jurassic group — Physical geography of the Oolite in England and France — Upper Oolite — Portland stone and fossils — Lithographic stone of Solenhofen — Middle Oolite, coral rag — Zoophytes — Nerinæan limestone — Diceras limestone — Oxford clay, Ammonites and Belemnites — Lower Oolite, Crinoideans — Great Oolite and Bradford clay — Stonesfield slate — Fossil mammalia, placental and marsupial — Resemblance to an Australian fauna — Doctrine of progressive development — Collyweston slates — Yorkshire Oolitic coal-field — Brora coal — Inferior Oolite and fossils - - -257

CHAPTER XXI.

oolite and lias — continued. Mineral character of Lias — Name of Gryphite limestone — Fossil shells and fish — Ichthyodorulites — 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 — Origin of the Oolite and Lias, and of alternating calcareous and argillaceous formations — Oolitic coal-field of Virginia, in the United States - - 273 CHAPTER XXH. TRIAS OR NEW RED SANDSTONE GROUP. Distinction between New and Old Red Sandstone — Between Upper and Lower New Red — The Trias and its three divisions — Most largely developed in Germany — Keuper and its fossils — Muschelkalk — Fossil plants of Bunter — Triassic group in England — Bone-bed of Axmouth and Aust — Red Sandstone of Warwickshire and Cheshire — Footsteps of Chirotherium in England and Germany — Osteology of the Labyrinthodon — Identification of this Batrachian with the Chirotherium — Origin of Red Sandstone and Rock-salt — Hypothesis of saline volcanic exhalations — Theoiy of the precipitation of salt from inland lakes or lagoons — Saltness of the Red Sea — New Red Sandstone in the United States — Fossil footprints of birds and reptiles in the Valley of the Connecticut — Antiquity of the Red Sandstone containing them - 286 CHAPTER XXHI.

PERMIAN OR MAGNESIAN LIMESTONE GROUP. Fossils of Magnesian Limestone and Lower New Red distinct from the Triassic — Term Permian— English and German equivalents — Marine shells and corals of CONTENTS. English Magnesian limestone — Palæoniscus and other fish of the marl slate — Thecodont Saurians of dolomitic conglomerate of Bristol — Zechstein and Rothlie gendes of Thuringia — Permian Flora — Its generic affinity to the carboniferous — Psaronites or tree-ferns ------ Page 301

CHAPTER XXIV. THE COAL OR CARBONIFEROUS GROUP.

Carboniferous strata in the south-west of England — Superposition of Coal-measures to Mountain limestone — Departure from this type in North of England and Scotland — Section in South Wales — Underclays with Stigmaria — Carboniferous Flora — Ferns, Lepidodendra, Calamites, Asterophyllites, Sigillariæ, Stigmariæ, — Coniferæ — Endogens — Absence of Exogens — Coal, how formed — Erect fossil trees — Parkfield Colliery — St. Etienne, Coal-field — Oblique trees or snags — Fossil forests in Nova Scotia — Brackish water and marine strata — Origin of Clay-iron-stone -----.. - 308

CHAPTER XXV. CARBONIFEROUS GROUP

— continued. Coal-fields of the United States — Section of the country between the Atlantic and Mississippi — Position of land in the carboniferous period eastward of the Alleghanies — Mechanically formed rocks thinning out westward, and limestones thickening — Uniting of many coal-seams into one thick one — Horizontal coal at Brownsville, Pennsylvania. — Vast extent and continuity of single seams of coal — Ancient river-channel in Forest of Dean coal-field — Absence of earthy matter in coal — Climate of carboniferous period — Insects in coal — Rarity of air-breathing animals — Great number of fossil fish — First discoveiy of the skeletons of fossil reptiles — Footprints of reptUians — Mountain limestone — Its corals and marine shells - - - - - -326

CHAPTER XXVL OLD RED SANDSTONE, OR DEVONIAN GROUP.

Old Red Sandstone of Scotland, and borders of Wales — Fossils usually rare "Old Red" in Forsarshire — Ichthyolites of Caithness — Distinct lithological type of Old Red in Devon and Cornwall — Term " Devonian " — Organic remains of intermediate character between those of the Carboniferous and SUurian systems — Corals and 6hells— Devonian strata of Westphalia, the Eifel, Russia, and the United States — Coral reef at Falls of the Ohio — Devonian flora ... 342

CHAPTER XX VH.

SILURIAN GROUP. Silurian strata formerly called transition — Term grauwacke — Subdivisions of Upper and Lower SUurian — Ludlow formation and fossils — Wenlock formation, corals and shells — Caradoc and Llandeilo beds — Graptolites Lingula Trilobites— Cystideæ— Vast thickness of Silurian strata in North Wales — Unconformability of Caradoc sandstone— SUurian strata of the United States— Amount of specific agreement of fossds with those of Europe — Great number of brachiopods— Deep-sea origin of SUurian strata— Absence of fluviatile formations Mineral character of the most ancient fossUiferous rocks - - . CONTENTS. XIII CHAPTER XXVIH. VOLCANIC ROCKS. Trap rocks — Name, whence derived — Their igneous origin at first doubted — Their general appearance and character — Volcanic cones and craters, how formed — Mineral composition and texture of volcanic rocks — Varieties of felspar Hornblende and augite — Isomorphism — Rocks, how to be studied — Basalt, greenstone, trachyte, porphyry, scoria, amygdaloid, lava, tuff — Alphabetical list, and explanation of names and synonyms, of volcanic rocks — Table of the analyses of minerals most abundant in the volcanic and hypogene rocks - Page 366

CHAPTER XXIX.

volcanic rocks — continued. Trap dike — sometimes project — sometimes leave fissures vacant by decomposition — Branches and veins of trap — Dikes more crystalline in the centre — Foreign fragments of rock imbedded — Strata altered at or near the contact — Obliteration of organic remains — Conversion of chalk into marble — and of coal into coke — Inequality in the modifying influence of dikes — Trap interposed between strata. — Columnar and globular structure — Relation of trappean rocks to the products of active voleanos — Sub-marine lava and ejected matter corresponds generally to ancient trap — Structure and physical features of Palma and some other extinct voleanos - - - - - ' - - - - 378

CHAPTER XXX. ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS.

Tests of relative age of volcanic rocks — Test by superposition and intrusion — Dike of Quarrington HU1, Durham — Test by alteration of rocks in contact — Test by organic remains — Test of age by mineral character — Test by included fragments — Volcanic rocks of the Post-Pliocene period— - Basalt of Bay of Trezza in SicUy — Post-Pliocene volcanic rocks near Naples — Dikes of Somma — Igneous formations of the Newer Pliocene period — Val di Noto in SicUy - - -397

CHAPTER XXXI. ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS

— Continued. Volcanic rocks of the Older Pliocene period — Tuscany —Rome — Volcanic region of Olot in Catalonia — Cones and lava-cm-rents — Ravines and ancient gravel-beds Jets of air caUed Bufadors — Age of the Catalonian voleanos — Miocene period — Brown-coal of the Eifel and contemporaneous trachytic breccias — Age of the brown-coal Peculiar characters of the voleanos of the upper and lower Eifel — Lake craters — Trass — Hungarian voleanos ... -408

CHAPTER XXXII. ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS

— Continued. Volcanic rocks of the Pliocene and Miocene periods continued — Auvergne — Mont Dor — Breccias and alluviums of Mont Perrier, with bones of quadrupeds — River dammed up by lava-current — Range of minor cones from Auvergne to the Vivarais — Monts Dome — Puy de Come — Puy de Pariou — Cones not denuded by general flood — Velay — Bones of quadrupeds buried in scoriæ — Cantal — Eocene volcanic rocks — Tuffs near Clermont — Hill of Gergovia — Trap of Cretaceous period— Oolitic period — New Red Sandstone period — Carboniferous period Old Red Sandstone period — "Rock and Spindle" near St. Andrew's — SUurian period — Cambrian volcanic rocks ... -422 CONTENTS. CHAPTER XXXHI. PLUTONIC ROCKS — GRANITE. General aspect of granite — Decomposing into spherical masses — Rude columnar structure — Analogy and difference of volcanic and plutonic formations — Minerals in granite, and their arrangement — Graphic and porphyritic granite — Mutual penetration of crystals of quartz and felspar — Occasional minerals — Syenite — Syenitic, talcose, and schorly granites — Eurite — Passage of granite into trap — Examples near Christiania and in Aberdeenshire — Analogy in composition of trachyte and granite — Granite veins in Glen Tilt, Cornwall, the Valorsine, and other countries — Different composition of veins from main body of granite — Metalliferous veins in strata near their junction with granite — Apparent isolation of nodules of granite — Quartz veins — Whether plutonic rocks are ever overlying Their exposure at the surface due to denudation - - - Page 436

CHAPTER XXXIV. ON

TnE 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 — Tertiary 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 — On the probable age of the granites of Arran, in Scotland - - - - - -449.

CHAPTER XXXV. METAMORPHIC ROCKS,

General character of metamorphic rocks — Gneiss — Hornblende-schist — Mica-schist Clay-slate — Quartzite — Chlorite-schist — Metamorphic limestone — Alphabetical list and explanation of other rocks of this family — Origin of the metamorphic strata — Their stratification is real and distinct from cleavage — Joints and slaty cleavage — Supposed causes of these structures — how far connected with crystalline action ....... 483

CHAPTER XXXVI.

metamorphic rocks — continued. Strata near some 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 — Time may enable this action to pervade denser masses — From what kinds of sedimentary rock each variety of the metamorphic class may be derived — Certain objections to the metamorphic theory considered — Lamination of trachyte and obsidian due to motion — Whether some kinds of gneiss have become schistose by a similar action - 473 CHAPTER XXXVH ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS. Age of each set of metamorphic strata twofold — Test of age by fossils and mineral character not available — Test by superposition ambiguous — Conversion of dense masses of fossUiferous strata into metamorphic rocks — Limestone and shale of Carrara — Metamorphic strata of modern periods in the Alps of Switzerland and CONTENTS.

XV Savoy — Why the visible crystalline strata are none of them very modern — Order of succession in metamorphic rocks — Uniformity of mineral character — Why the metamorphic strata arc less calcareous than the fossiliferous - - Page 48 1 Page 481 CHAPTER XXXVni. MINERAL VEINS. Werner's doctrine that mineral veins were fissures filled from above — Veins of segregation — 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 — Shells and pebbles in lodes — Evidence of the successive enlargement and re-opening of veins — Fournet's observations in Auvergne — Dimensions of veins — Why some alternately swell out and contract — Filling of lodes by sublimation from below— Chemical and electrical action — Relative age of the precious metals — Copper and lead veins in Ireland older than Cornish tin — Lead vein in lias, Glamorganshire — Gold in Russia — Connection of hot springs and mineral veins — Concluding remarks - - -489 Dates of the successive Editions of the "Principles " and " Elements " (or Manual) of Geology, by the Author.

Principles, 1st vol. in octavo, published in - - - - Jan. 1830. , 2d vol. do. ----- - Jan. 1832. , 1st vol. 2d edition in octavo - 1832. , 2d vol. 2d edition do. - - - - - Jan. 1833. , 3d vol. 1st edition do. - - - - - May 1833. , New edition (called the 3d) of the whole work in 4 vols. 12mo. ._..__ May 1834. , 4th edition, 4 vols. 12mo. .... June 1835. ■ , 5th do. do. do. .... Mar. 1837. Elements, 1st edition in one vol. ..... July 1838. Principles, 6th do. 3 vols. 12mo. ... - June 1840. Elements, 2d edition in 2 vols. 12mo. .... July 1841. Principles, 7th edition in one vol. 8vo. .... Feb. 1847. , 8th edition now published in one vol. 8vo. - - May 1850. Manual of Elementary Geology (or " Elements," 3d edition), now published in one vol. 8vo. .... Jan. 1851. Works by Sir Charles Lycll. i. TKAVELS IN NORTH AMERICA, — 1841-2.