An Introduction to Geology, illustrative of the general structure of the earth; comprising the elements of the science, and an outline of the geology and mineral geography of England. The third edition, entirely recomposed and greatly enlarged. With new plates

Introduction

TO GEOLOGY: COMPRISING THE ELEMENTS OF THE SCIENCE IN ITS PRESENT ADVANCED STATE, ANl) ALL THE RECENT DISCOVERIES; WITH AN OUTLINE OF THE GEOLOGY OF ENGLAND AND WALES By ROBERT BAKEWELL. THE THIRD EDITION, ENTIRELY RECOMPOSED, AND GREATLY ENLARGED. WITH NEW PLATES. LONDON: PRINTED FOR LONGMAN, REES, ORME, BROWN, AND GREEN- PATERNOSTEK-ROW. 1828. LONDON : PRINTED BY RICHAKD TAYLOR, RED LION COURT, FLEET STREET.

Preface

TO THE THIRD EDITION. 1 HE First and Second Editions ofthe Introduction to Geology were favourably receivedand sold off, soon after their publication. The work has since been translated and published in Germany, by Mr. Frederick Muller of Friburg; but it has been long out of print in this country. The causes which have retarded the publication of a Third Edition it is unnecessary to mention : the delay has, I trust, been favourable to its appearance in a very im proved state ; as I have been collecting materials for it, during several years, having visited almost every situation of much geological interest in our own island, from the Land's End in Cornwall, to the Grampian Mountains in Scotland ; and passed part of three years in examining the geology of Savoy, Switzerland, and France. There is scarcely a rock formation described in the present volume, that I have not examined in its native situation, and com pared with the descriptions of former geologists. I have also had opportunities of examining the collec tions, and of profiting by the communications, of a2

PREFACE.

TO some of the most eminent geologists on the Conti nent. While engaged in these pursuits, I have not been inattentive to the labours of other observers. So numerous and interesting are the discoveries made in geology during the last ten years, that in order to present a concise view of the science in its present advanced state, the Introduction to Geology has been recomposed, and all the Chapters are greatly enlarged. The following new Chapters have been added : — Chap. ii. On Fossil Organic Remains. Chap. iv. On the Principles of Stratification. Chap. x. A Re trospective View of Geological Facts. Chap. xvm. On the Destruction of Mountains; and on the Bones of Land Quadrupeds, found in Diluvial Depositions and in Caverns. Chap. xix. On the Formation of Valleys; and on Deluges and Denuda tions. — The Plates are new, except Plate iv. and part of Plate vii.

The Outline Map of the Geo logy of England and Wales, was I believe, when published in the First Edition of 1813, the only geological map of England that had then appeared. It presents in one view the grand geological divi sions of the country, without delineating the differ ent strata in each division. Mr. Wm. Smith has since published a map of the Geology of England, which possesses extraordinary merit, — when it is considered as the unaided attempt of one person, to trace the course of each rock formation through THE THIRD EDITION. V England and Wales. Mr. Greenough, and other members of the Geological Society of London, have subsequently published a geological map of En gland and Wales. This map, from the great variety of its useful details, and its general correctness, may be regarded as the most complete exhibition of the geology of an extensive country, that has yet appeared.

It was thought, however, that the publication of my Map in its original form, (or nearly so,) would be acceptable to those who wished to gain a general knowledge of the geology of their own country, without entering into geological details ; and that it would also serve as a useful introduction to the study of the above-mentioned maps. In the course of the present work, I have fre quently attempted to elucidate the geology of En gland, by comparisons with situations I have exa mined on the Continent, in order to connect the geology of our own island, with that of France, Switzerland, and Savoy. By comprising the numerous facts and observa tions contained in the present volume, within the limits of an elementary work, from the desire to be concise, I may have run the risk of becoming obscure : this I have studiously endeavoured to avoid; my chief aim being to present the reader with a system of Geology, which shall explain geo logical phenomena in a clear and intelligible man ner, and as free from technical obscurity as the VI

PREFACE.

TO nature of the subject would admit. In order that the price may not exceed that of the last Edition, this work is printed in a smaller type. For any errors into which I may have inadvertently fallen, I would claim the candid indulgence of the reader, in the last words of that distinguished geologist Horace Benedict de Saussure, " On peut 6tre utile, sans atteindre d la perfection." 1 shall conclude with some observations on the means of advancing geological knowledge. In a conversation I had with that experienced geologist Professor Brochant at Paris, on this subject, — he said: "We are already sufficiently rich in facts, what is now wanting, is an accurate review of these facts : many geological descriptions, on which much stress continues to be laid, were written in an early state of the science, and require such corrections, as a comprehensive view of recent discoveries could scarcely fail to suggest. — I should recommend, Sir, that two active young men, competently instructed, should be sent out to examine all the most remark able situations described by former geologists, and to note down their observations on the spot.

They should travel together, not only for the sake of mutual comfort and assistance, in the solitary situa tions they might have to visit, but in the examina tion of dubious phenomena, that the observations of the one might correct or confirm those ofthe other." —These remarks of M. Brochant, which I have given as correctly as my memory and the difference THE THIRD EDITION. VII of language would allow, well deserve the attention of all Geological Societies*. What appears to me much wanted to clear up several dubious points in Geology, is a series of experiments, to ascertain the relative position and connection of certain rocks. This in some instances might be effected, by employing workmen to open out the edges of strata : other cases would require shafts to be sunk, and passages to be driven into the sides of mountains.

Such experiments would be attended with expense; but they would reward us by the discovery of important facts, which must otherwise remain for ever unknown. * A Geological Map of France is at present in progress, under the direction of Professor Brochant. Hampstead, near Londox, March 10, 1828. PREFACES TO THE FIRST AND SECOND EDITIONS ABRIDGED. IN tracing the progress of knowledge, we may frequently observe that the cultivation of particular branches of science at certain periods, was deter mined by causes which had little connection with their intrinsic utility. Fashion, caprice, and the authority of eminent names, govern mankind in philosophy, as well as on all Other subjects. But, independently of accidental causes, there are leading objects in the universe, which, as nations ad vance in civilization, seem naturally to direct their attention to certain sciences in succession.

The brilliancy of the sun, moon, and planets, their va rious motions, and connection with the changing seasons, would first arrest the attention of the rude philosopher; nor need we wonder, that he soon began to regard them as endowed with life and intelligence, and attributed to them a mysterious power over human affairs : thus the heavenly orbs became the objects of religious adoration ; and curiosity, hope, and fear, lent their aid to the early cultivation of astronomy. PREFACES TO THE FIRST AND SECOND EDITIONS, Mathematics and mechanical philosophy are so intimately connected with astronomy and the most useful arts, that they naturally claimed the second place among the early sciences. The branches of philosophy which comprise a knowledge of the physical qualities of matter, or such as are perceptible by the senses, follow next ; and at a later period, chemical philosophy or that science which endeavours to ascertain the elementary substances, of which all material objects are composed.

In the order of succession, mineralogy and geology are the last of the natural sciences ; for though an acquaintance with the earth is more important to man than a knowledge of the distant parts of the universe; yet, previously to the cultiva tion of the other sciences, and of chemistry in par ticular, our knowledge of the mineral kingdom could not extend much beyond that of the rudest periods. Thus we find that notwithstanding the precious metals, and many of the mineral treasures which the earth contains, have been the objects of insatiable cupidity in every age, yet, till the present day, almost all that was known of mineralogy, was confined to uneducated working miners. In looking over the pages of history, we may observe that the most polished nations of antiquity had scarcely advanced beyond a limited acquaint ance with astronomy, geometry, and mechanical philosophy.

In modern Europe, all the natural sciences, geology and mineralogy excepted, have X PREFACES TO THE been successfully cultivated, and their progress has been astonishingly rapid ; but till about the middle of the last century, the structure of the earth had scarcely engaged the attention of philosophers. Near that time, Lehman, the German, first ob served that there are certain rocks which occupy the lowest relative situation in different countries, and that these rocks contain no organic remains : hence he gave them the name of primary, and established a division between them and the rocks by which they are covered, in which the remains of animals or vegetables frequently occur : the lat ter he called secondary. In our own country, the Reverend J. Michel!, was the first person who ap pears to have had any clear views respecting the structure of the external parts of the earth : they were made public in a valuable paper on the cause of earthquakes, in the Philosophical Transactions, 1759.

About twenty years afterwards, Mr. John Whitehurst published his " Inquiry into the original State and Formation of the Earth." His observations were principally confined to the rocks and strata of Derbyshire. Independently of its speculative opinions, this work was highly valuable, as an attempt to describe the geology of a district, from actual examination. The great variety of original information it contained, and its general accuracy, will remain a lasting monument of the writer's industry and ability. Mr. Whitehurst, however, fell into the same error with the cele- FIRST AND SECOND EDITIONS. XI brated Werner in Saxony, an error to which the first cultivators of geology were particularly ex posed, — that of drawing general conclusions from local observations, and forming universal theories from a limited number of facts.

Though Mr. Whitehurst's book was favourably received, yet till the beginning of the present cen tury geological pursuits made little progress in En gland. On the continent, the researches of Saus sure, Pallas, Werner, St. Fond, Dolomieu, and others, had before this time produced a powerful interest, and brought into the field many active and enlightened inquirers. The first general impulse given to the public taste, for geological investiga tions in this country, was produced by Professor Playfair's luminous and eloquent illustrations of the Huttonian theory. The leading feature of this theory, that all rocks or strata have been either formed or consolidated by central subterranean fire, was very warmly opposed ; and much personal animo sity and many adventitious circumstances were as sociated with the contest, not highly honourable to philosophy, but well calculated to keep alive the attention of the disputants, to those appearances in nature, which favoured or opposed their different theories.

He who attempts to make a scientific subject familiar, runs the risk in this country of being deemed superficial : a plentiful share of dullness, combined with a certain degree of technical pre- PREFACES TO cision, are regarded as essential proofs of pro fundity. By prescriptive right, long established in these realms, dullness and pedantry guard the por tals of the temple of Science, and command those who enter, to avert their eyes from whatever can elevate the imagination, or warm the heart, and to look at nature through a sheet of ice. In com pliance with their authority, writers of introductory treatises, have generally thought it necessary to avoid that felicity in the familiar illustration of scientific subjects, so conspicuous in some of the elementary works of our neighbours. Without venturing to depart too far from established usage, I have endeavoured to render geology more intelligible, by avoiding as much as possible theoretical and technical language, and by introducing a simple arrangement, suited to the present state of our knowledge.

The local illustrations from various parts of our island, with the drawings, sections, and map in the present volume, will I trust facilitate the study of geology, and prove particularly acceptable to those who are entering on these inquiries : at the same time, I flatter myself with the hope, that the original information this work contains, respecting the geology and natural history of England, will secure it a candid reception. — Edition of 1813. Several have been deterred from the study of geology by the supposed difficulty of learning its attendant science, mineralogy ; but an acquaintance with the nice distinctions made by many modern THE FIRST AND SECOND EDITIONS. XIII mineralogists, is not necessary to gain a knowledge of the structure and arrangement of the great masses of matter that environ the globe, nor of the substances of which they are composed.

He who would gain a useful knowledge of geology, would do well to provide himself with specimens of com mon rocks, and the simple minerals of which they are composed, and examine their external characters and physical properties, comparing them with the descriptions given by the best mineralogical writers. Fortunately these substances are not very numerous, and he may (without present inconve nience) omit the more rare crystallizations and varieties, so much valued by cabinet philosophers ; for here, as in many other instances, the received value, is in an inverse ratio ofthe utility. The pe dantic nomenclature, and frivolous distinctions re cently introduced into mineralogy, may gratify vanity with a parade of knowledge ; but they are unconnected with objects of real utility, or with any enlarged views of nature.

On hearing the various names which mineralo gists give to the same substance, and observing the avidity with which each new name is seized, as if it conveyed a hidden charm, the uninitiated might suppose, that he was "journeying in the land of Shinar," and had fallen in company with a set of masons fresh from the tower of Babel, each one calling the same stone by a different name, and glorying in his absurdity. Such frivolities disgust PREFACES TO THE FIRST AND SECOND EDITIONS. men of sense with the study of an important and interesting science; a science that has for its imme diate object, the structure of the planet which the Author of nature has destined for our abode, and an acquaintance with the situation of its various mineral productions, subservient to the wants or enjoyments of man in civilized society.

The advice of Cicero to the cultivators of moral science, applies with peculiar force to the geologists and mineralogists of the present day. " In these natural and laudable pursuits, two errors are particularly to be avoided : the first, not to confound those things of which we are ignorant with those we know, or rashly to yield our assent without due investigation ; the second, not to bestow too much labour and study on obscure, intricate, and unprofitable subjects." "In hoc genere et naturali et honesto duo vitia vitanda sunt : unum, ne incognita pro cognitis habeamus, hisque temere assentiamur (quod vitium effugere qui volet adhibebit ad considerandas res et tempus et diligentiam). Alterum est vitium, quod quidam nimis magnum studium multamque operam in res obscuras atque difficiles conferunt, easdemque non necessarias." — Cic. Qf fic. i. 6. CONTENTS.

Chapter I

Objects of the Science denominated Geology. — The Shape and Density of the Earth. — Opinions respecting the internal Parts of the Globe. — Sea and dry Land. — Proportion of the Earth's Surface habitable by Man. — On the Appearances which led to the first Division of Rocks into Primary and Secondary. — Classification of Rocks. — Districts in which the different Classes appear in England. — The present Islands and Continents formerly covered by the Ocean. — Existing Proofs of this in Great Britain and various Parts of the World. — Fossil Remains of marine Animals, Vegetables, and Land Quadrupeds j the Strata in which they are imbedded formed in Succession at different Epochs. — On human Bones occasionally imbedded in Rock. — Inferences respecting the former Condition ofthe Globe. — Remarkable Passage in the Institutes of Menu. . . . Page 1

Chapter II. On Petrifactions, Or Fossil Organic Remains

Opinions of early Naturalists respecting Petrifactions. — On the Process called Petrifaction in some Instances rapidly effected. Experiment of Dr. Jenner on the Petrifaction of recent Bones. — Living Reptiles occasionally found in solid Stone. — Remarkable Difference in the Condition of Fossil Remains in adjacent Strata; Instance of this at Westbury Cliff, Gloucestershire. — The four grand Divisions of the Animal Kingdom. — Distribution of the Remains of certain Classes and Orders of Animals in each Division through the different Rock Formations. Remains of Monkeys hitherto undiscovered in a Fossil State. Page 27 Observations on Fossil Organic Remains, as serving to identify Strata in distant Countries. Page CONTENTS.

Chapter III. On The Mineral Substances That Compose The Crust Of The

GLOBE; AND ON THE STRUCTURE OF ROCKS. The constituent Elements of the simple Minerals that compose Rocks. — The physical Characters of simple Minerals composing Rocks. — Explanation of the Terms employed in describing the internal Structure of Rocks, and the external Structure of Mountain Masses Page 46

Chapter IV. On Stratification, And The Relative Position Of Rocks

The Principles of Stratification explained. — Various Appearances presented by plain Strata. — Appearances presented by curved Strata, and Errors respecting them. — Distinction between Strata-seams, and Natural Fissures or Cleavages. — On the conformable and unconformable Positions of stratified and unstratified Rocks. — The Intersection of stratified Rocks by Valleys explained. — Longitudinal Valleys. — Transverse Valleys. — Lateral Valleys. — On the Elevation of Mountains and Mountain Chains. — On the Direction of Mountain Chains in the new and old Continents. — On vertical Beds in Mountains. — On the apparent Devastation in Alpine Districts. — On the Passages in the Alps called Cols ; and Observations respecting their Formation Page 63

Chapter V. On Rocks Generally Denominated Primary

Classification of Primary Rocks. — Granite ; its constituent Minerals. — Varieties of Granite.— Structure of Granitic Rocks. — General Appearance of Granitic Mountains.— Granitic Aiguilles. — Structure of Mont Blanc— Principal Localities of Granite. — Situations in England where Granite is found. — Granite Veins — On what has been denominated Secondary Granite.— On the Passage of Granite into Felspar-Porphyry, and Sienite.— Minerals that occur in Granite; Uses to which it is applied page CONTENTS. XVII

Chapter VI. On Gneiss, Mica-slate, And The Rocks Which Are Frequently Associated

WITH THEM. On the Passage of Granite into Gneiss. — Gneiss and Granite veini. — Mica-Slate. — Crystalline or Primary Limestone. — Formation of Lime by Animal Secretion. — Origin of Calcareous Rocks. — Serpentine.— Euphotide or Saussurite. — Hornblende Rocks. — Compact Felspar. — Eurite, or White Stone. — Primary Porphyry a Mode of Granite. — Recurrence of the same Rocks in different Rock-formations Page 1 08

Chapter VII. On Transition Or Intermediate Rocks

Character and Classification of Transition Rocks. — Slate, the Clay-slate of Werner. — Roof Slate, its Cleavage not the Effect of Stratification, but of Crystallization. — Talcous Slate. — Whetstone Slate. — Flinty Slate. — Greywacke and Greywacke Slate, its Passage into Red Sandstone and Gritstone. — Errors of English and Foreign Geologists respecting the Old Red Sandstone and Mountain Limestone. — Old Red Sandstone. — Transition Limestone. — Transition Limestone of Devonshire, and Dudley in Staffordshire. — Upper Transition or Mountain Limestone. — Its Connection with Coal Strata.— :Jasper. . . . Page 1 24 Observations on the Fossils in Transition Rocks, and on the variable order of succession in Rocks of this Class Page 143

Chapter VIII. On The Lower Secondary Strata Comprising The Re- Gular Coal

FORMATION. The relative Geological Position of Coal Strata. — Wood Coal. — Mineral Coal. — Arrangement of the Strata in Coal-fields. — Concavities or Basins in which Coal Strata are deposited. — Intersections by Faults or Dykes. — Their Effects on Water in Coal Mines. — Peculiar Positions of Coal Strata in certain Districts. — On the Mode of Searching for Coal. — Ironstone accompanying Coal. — Precautions necessary in the Establish- CONTENTS. XVIII ment of Iron Furnaces. — On Carbon as an original constituent part of the Globe.— On the Origin of Coal and its Deposition in Freshwater Basins or Lakes. — Experiments of Dr. MacCul loch on the Conversion of Vegetable Matter into Coal. — On imperfect Coal Formations beyond the limits of the regular Coal Strata.— Hints to Landed Proprietors respecting the probability of finding Coal and Rock Salt in Districts where they are at present undiscovered. — Coal Mines in France, &c. — On the Consumption of Coal in England, and the period when it will be exhausted Page 146 Observations on the Period when the Coal Mines in England will be exhausted .... Page 178

Chapter IX. On Unconformable Rocks Of Porphyry, Trap And Basalt, And On

BASALTIC DYKES. The different Positions of Conformable and Unconformable Massive Rocks described. — Opinions respecting the formation of Unconformable Massive Rocks. — Varieties of Trap Rocks ; their Passage by Gradation into each other and into Volcanic Rocks. — Porphyry, Porphyritic Trap, Greenstone, Sienite, Clinkstone, Basalt, Amygdaloid, Wacke, Pitchstone. — Passage of Porphyry and various Trap Rocks into each other, and into Sienite and Granite, at Christiania in Norway. — Passage of Basalt into scoriaceous Lava and Obsidian. — Mountains of Porphyritic Trap and Clinkstone with deep Craters, probably formed by depression. — High Stile, Cumberland. — Cader Idris, Wales. — Basaltic Dykes. — Columnar and Massive Basalt. — Interstratified Basalt. — Strata confusedly broken and enveloped in Basalt. — Organic Remains enveloped in Basalt. — Basalt of Scotland, Ireland, Auvergne, and Iceland. — On the formation of Basalt. — Experiments of Mr. Watt. — Theory of Werner.— On the relative age of Trap Rocks Page 1 32 Observations Page 218

Chapter X

A RETROSPECTIVE VIEW OF CERTAIN GEOLOGICAL FACTS AND INFERENCES STATED IN THE PRECEDING CHAPTERS P. CONTENTS. XIX

Chapter XI. On The Upper Secondary Rocks

On the Mineral and Zoological characters which distinguish Rocks of this Class. — Large Saurian Animals. — Magnesian Limestone or Dolomite. — On the occurrence of Magnesian Earth in Calcareous Rocks. — Compact and cellular Magnesian Limestone. — English Strata of Magnesian Limestone compared with those on the Continent of Europe. — Red Marie and Sandstone. — Variety of its Mineral characters. — The accordance of the English Strata of red Marie with those of France and Germany ascertained. — The red Marie and Sandstone of the Vosges. — English red Marie and Sandstone formed principally of the fragments of Trap Rocks and Transition Rocks, which formerly covered the midland parts of England. — Rock-salt and Gypsum. — The Gypsum accompanying Rock-salt originally anhydrous. — Rock-salt formations in various parts of the world. — On the invariable association of Gypsum with Rock-salt Page 232

Chapter XII. On Part Of The Upper Secondary Strata Comprising Lias Clay

AND LIMESTONE, AND THE OOLITIC SERIES. Mineral Characters of Lias Clay and Limestone. — Alum Slate. — Zoological Characters of Lias. — The Muschelkalk of France and Germany, the lower part of the Lias Formation, wanting in England. — Lias of the Alps. — Oolite or Roestone, the Jura Limestone of Foreign Geologists.— -Mineral and Zoological Characters of Oolite or Roestone. — The lower, middle, and upper Oolites. — Oxford or Clunch Clay. — Stonesfield Slate, with Organic Remains of Insects, Birds, and Land Quadrupeds. — Extent of the Oolite Formation in England ; its sudden termination : Observations respecting it. — Foreign Oolites. — Page 261 Observations Page 276

Chapter XIII. On Chalk, And The Subjacent Strata Containing Re- Mains Of

LAND PLANTS AND FRESHWATER ANIMALS. Remarkable Zoological Characters of the Strata between the Upper Oolites and Green-sand. — Purbeck beds — Iron-sand. — XX CONTENTS. Tropical Plants and gigantic Animal Remains discovered in it. — Supposed appearance of the country at the period when these Aninwls flourished.— Green-sand.— Chalk-marle. — Lower Chalk— Chalk with Flints.— Thickness and extent of Chalk in various countries. — Inferences from the condition of the Fossils found in Chalk.— Observations on the State of the Upper Secondary Strata previous to the deposition of the Tertiary Strata Page 278

Chapter XIV. On The Tertiary Formations

On the Formation of the Tertiary Strata in Lakes or inland Seas. — On their subsequent destruction by external causes. — On the discovery of the Tertiary Strata of Fiance. — Alternations of Marine and Freshwater Strata. — General Classification of Tertisiry Strata. — Lower Marine Strata sometimes alternating with Beds containing River Shells and Lignite. — Lower Freshwater Strata sometimes containing Marine Shells. — Upper Marine Sandstone. — Upper Freshwater Limestone. — Plastic Clay and London Clay.— Molasse. — On the Remains of Land Quadrupeds supposed to be found in Molasse. — On the London Clay in the Vale of Thames, and the Strata with pure Water below it. — Calcaire grossier and Calcaire siliceux. — Gypseous Marie and Gypsum of Paris containing Bones of rilimerous extinct Species of Land Quadrupeds. — Upper Marine Sandstone of France and England. — Freshwater Limestone of Paris and the South of France. — Remarkable position of the Tertiary Strata in the Isle of Wight. — Opinions respecting the alternation of Marine and Freshwater Formations Page 294 Observations Page 327

Chapter XV. On Earthquakes And Volcanic Phenomena

— ON RE- CENT AND ANCIENT VOLCANOES. SUBMARINE VOLCANOES. — AND ON VOLCANIC ROCKS AND PRODUCTS. Page 330 Observations Page 380

Chapter XVII. On The Repositories Of Metallic Ores

Metallic Matter disseminated through Rocks. — Masses of Metallic Ore. — Metallic Beds. — Metallic Veins. — Rake Veins. — Flat Veins. — Accumulated Veins. — Cross Courses.— The remarkable Structure of the Botallack Mine worked under the Sea. — On the Formation of Metallic Ores. — Remarkable Phenomena in Mines. — Stream Works. — Rocks in which certain Metallic Ores are found Page 394

Chapter XVIII. On The Destruction Of Mountains

— ALLUVIAL AND DI- LUVIAL DEPOSITIONS. — THE FORMATION OF SOILS. AND ON THE BONES OF QUADRUPEDS IN BEDS OF GRAVEL AND CLAY, AND IN CAVERNS. Proofs of the Disintegration of Rocks. — The rapid destruction of Mountains dependent on their Structure. — The Fall of Mont Grenier and other Mountains in the Alps. — The breaking down of the Barriers of Mountain Lakes. — Masses of Rock scattered over Valleys and Hills. — On the Increase and Decrease of Continents and Islands, and the Formation of productive Soils. — Recent Strata formed in Lakes. — Peat and Peat Moors. — Human Bodies preserved in Peat. — Inundations of Sand. — Coral Islands. — The Remains of Land Quadrupeds found in Bogs, in Beds of Clay or Gravel, and in Caverns. . Page 421

Chapter XIX. Geological Theories

— THE FORMATION OF VALLEYS. DE- LUGES, and denudations. Page 466

Chapter XX. An Outline Of The Geology Of England And Wales

Page 483 (See Index " Geology of England") Appendix Page 521 Index Page DESCRIPTION OF THE PLATES. Plate V. The Gigantic Trilobite of the natural size (to face the title). From a specimen in the Author's collection. — This specimen was taken from the slate quarries at Angers in France. The animal has received the name of Ogyges ; it is supposed to be one of the oldest inhabitants ofthe globe. The living animal which resembles it the most, is the Monoculus Apus. Plate I. Fig. 1. 2. 3.4.5. 6. Illustrations of plane and curved stratification. (See Chap. IV.) Plate II. Fig. 1 . Overlapping strata with straight edges. Fig. 5. Overlapping strata with curved edges. Fig. 2. Structure of a part of the Alps, representing the beds, nearly vertical, that approach the central range, and the bended stratification of the outer ranges.

The dotted lines represent the supposed extension of the beds at the period of their elevation, d d. granite and mica-slate. c c. beds of soft slate, a a a. b b. beds of limestone, sandstone, and conglomerate. Fig. 4. A section representing the arrangement of the rocks and strata at Charnwood Forest in Leicestershire, from the manor of Whitwick, to near Barrow-on-Soar. In this section the proportions of distance are disregarded, in order to bring the different rock formations within the space of the plate, a a a. stratified sandstone. b b. rocks of granite, sienite, and porphyry, c: c. slate-rocks of Swithland quarry ; the beds much elevated, d d. coal strata, rising towards the granitic and slate-rocks, e. lias, covering the red marie. It is obvious from this arrangement, that the strata of sand- DESCRIPTION OF THE PLATES.

XXIII stone a a a. were deposited upon the slate-rocks and granite, after the beds had been raised into their present position : whereas in Fig. 2. the beds a a. have evi dently been deposited before the beds of granite in the Alps were elevated ; and as these beds a a. are of more recent formation than the sandstone a a. in Fig. 4. their position proves decidedly, that the beds of granite in the Alps, were elevated after the beds of granite and slate in Leicestershire. (See Chap. X.) Fig. 3 Fig. 6 A granite vein in slate. The remaining portion of a thick bed of limestone forming an isolated mass b. on a mountain in Savoy, a a. the former extent of the bed. cc. a bed of soft sandstone. Plate III. Fig. 1 The conformable position of rocks, a. granite, b. gneiss. c. mica-slate, d d. slate, x x. a subordinate bed of limestone on slate. 2. a bed of conglomerate, e e. transition limestone and greywaeke. e. upper conglomerate, f f. coal strata.

Fig. 2 a. Unconformable massive rocks. A thick bed of porphyry or basalt, c. c. covering the transition rocks 1. 2. 3. and dykes of porphyiy or basalt intersecting transition rocks. — N. B. The porphyry at Christiania in Norway occurs in this position ; the lower part of it is amygdaloidal basalt ; the middle part is porphyritic, which passes in the upper to beautiful sienite and common granite. (Seepage 190.) The rocks b. on the right, represent the three modes of basalt : — a columnar bed, d. with a vertical dyke of basalt, and beds of interposed basalt, b, is an isolated cap of columnar basalt. Fig. 3, Unconformable strata of sandstone, covering coal strata on the side of the dip b. and on the side of the rise d. (See page 1 75 .) Fig. 4 A section representing the general arrangement of the strata near Dudley, a. Wren's Nest Hill, a, b. two elevated beds of limestone, the lower of which is worked by horizontal passages over each other.