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 fifth edition considerably enlarged ... with new sections and cuts

Introduction

TO GEOLOGY: INTENDED TO CONVEY A PRACTICAL KNOWLEDGE OF THE SCIENCE, AND COMPRISING THE MOST IMPORTANT RECENT DISCOVERIES; WITH EXPLANATIONS OF THE FACTS AND PHENOMENA WHICH SERVE TO CONFIRM OR INVALIDATE VARIOUS GEOLOGICAL THEORIES. BY ROBERT BAKEWELL. THE FIFTH EDITION, CONSIDERABLE ENLARGED FROM THE FOURTH EDITION, AND WITH NEW SECTIONS AND CUTS. LONDON: PRINTEn FOR LONGMAN, ORME, BROWN, GREEN, & LONGMANS, PATERNOSTER-ROW. 1838. London : Printed by A. Spottiswoode, New-Street- Square.

Preface

TO THE FIFTH EDITION. Ihe additional facts and observations introduced into various parts of the present Edition, together with several new cuts and sections, and one new chapter, have considerably increased its size, but the price will remain the same as that of the Fourth Edition. The new Chapter, Nine, relates to a general fact, which has hitherto almost escaped the attention of Geologists : — " On the removal and disappearance of coal strata, raised above the surface of the ground by Faults, and on the probable causes of this re moval." Whether the causes assigned by the Author shall be deemed satisfactory or otherwise, he trusts he has rendered a useful service to Geology, by directing tlie attention of enquirers to the subject. a

PREFACE.

TO On re-examining with attention the First Edition of this work, published twenty-five years since (1813), the Author has felt satisfaction in observing, that many* of his opinions in Geology, which were then new, have been proved to be correct, by subsequent discoveries. He has been more particularly gratified by finding, that his anticipations of the agency of Voltaic Electricity, in the formation of metallic ores, and his suggestions that the different electrical conditions of adjacent rocks, contributed to the separation and deposition of metallic matter in veins, appear to have received a full confirmation, by the interesting experiments of Mr. Crosse. What the Author stated on this subject in the Edition of 1813, has been republished, ver batim, in all the subsequent Editions, and is given in the present Volume, pp. 499, 500 ; to which, and the observations, pp. 506 and 507, he refers the reader.

In the Preface to the Fourth Edition of this work, it was stated, that endeavours were made by some continental conchologists, to establish the doctrine, that fossil conchology, independent of the succession and stratification of rocks, is the true basis of Geo logy. In this country, attempts to divert Geology from its proper object, appear to be in some instances progressive. In order to enhance the value of organic remains, it has been said, that the mineral covering of the globe is the mere brick and mortar of the edifice, and of course entitled to little consideration ; and, in a definition of Geology, given in an ingenious and popular work, the knowledge of the mineral com- THE fifth edition. V composition, and arrangement of the rocks and strata is omitted, and the science is limited to " the investigation of the changes that have taken place in the organic and inorganic kingdoms of nature, and their causes."

(see note, p. 4.) The Author believes, that this is what the Germans call a one-sided view of the science, and he ventures to maintain, that the principal object of Geology is to investigate the composition and contents of different rocks or strata, together with their position, and arrangement, and their order of succession. Without this knowledge, we can obtain no satisfactory information whatever, respecting the former changes which the surface of the earth has under gone. This may be made obvious to any person of sound understanding, whether he be a Geologist or not. Suppose him to pass near the steep escarpment of a hill or cliff, in which the strata are distinctly exposed to view, and that their position was highly inclined or nearly vertical. If he examined them closely, he might find some of the strata composed of clay more or less indurated, others of sand and sandstone, and among these he might observe strata containing rounded or water-worn pebbles, and some beds with oyster shells, or other species of aquatic shells.

A little reflection would convince him, that these beds had been deposited under water, like the beds of mud or sand in seas or lakes. If such was their a VI

PREFACE.

TO mode of formation, they must originally have been deposited in a position nearly horizontal, but the strata he is examining are now nearly vertical ; hence he is assured, that their position has been changed since their deposition. Thus, by a knowledge of the composition of the beds, and their arrangement in a vertical position, he discovers two important geological events, which he could not otherwise have ascertained. In almost all descriptions, in which it is attempted to demonstrate the former changes of the earth's surface, the evidence, to be of any value, must be supported by references to the present structure and arrangement of the mineral crust of the globe ; this forms the basis of all sound geological inductions. Fossil organic remains, how ever interesting to the Botanist or Zoologist, are chiefly valuable to the Geologist, by enabling him to trace the succession of distant beds where their continuity is interrupted, and also to discover the alternations from marine to fresh-water formations, and in some instances, they serve to indicate the former condition and temperature of the earth.

The changes of the earth's surface, which take place during the short interval of one generation, are seldom of sufficient magnitude, to effect any distinguishable alteration in the physical outline of a country ; but by connecting these changes with those, which the investigation of the structure of the crust of the earth, proves to have taken place in remote ages, we are enabled to unrol some pages of THE FIFTH EDITION. VII the Volume of Nature, that disclose a portion of the ancient history of the globe. The investigation of the past changes which the earth has undergone, forms a valuable branch of the science of Geology ; the chapters relating chiefly to this subject, are placed in the latter part of the present Edition, and are separated from the pre ceding chapters by a distinct Title-page, and a brief notice.

Hampstead, near London. March 29, 1638. A vm Part of Professor Sitlimans Preface to the American reprint of ihe Third and Fourth Editions. The Editor believes that he is performing a service to his country, by encouraging the republication of a work conspicuous for attractiveness — for perspicuity — for a style generally vigorous and correct — often eloquent and beautiful ; and for an independence of spirit, which carries the Author straight forward to his object, certainly without any servile regard to previous systems. While bestowing this merited commendation, we do not mean to say, that we fully adopt all the Author's theoretical views, although most of them appear to be philosophical and just, and some of them are peculiarly happy. Speaking in the character of a public instructor of youth, I beg leave to add, that my immediate motive for recommending the re publication was, that I might place in the hands of my own classes, a comprehensive Treatise on Geology, which they would be willing to read and able to understand.

PREFACE.

TO THE FOURTH EDITION. The present Volume contains above one fourth more letter press than the Third Edition : being printed closer, and in a fuller page, in order to comprise numerous additional facts, and the important discoveries recently made in Geology. There are five entirely new chapters, beside considerable ad ditions to most of the former chapters. .( Since the publication of the Third Edition, the Author has revisited several of the localities which were the scenes of his earliest investigations ; he has also examined certain parts of England, of which the geology was dubious ; and has inserted in this work such alterations as were deemed necessary. These, however, bear a small proportion to the valuable labours of foreign and English geologists, during the last five years, of which an account is given in different parts of the volume.

In a preliminary dissertation, on certain living species of animals that elucidate fossil conchology, and also in the work itself, the Author has endeavoured to direct the attention of geological students to a subject hitherto much neglected. Great importance is attached to the study of fossil shells ; but the character of the animals that inhabited them, or the power they might possess of modifying the form of the shell under various circumstances, has scarcely been thought of. Some French conchologists are endeavouring to establish the doctrine, that fossil conchology, independent of the succession and stratification of rocks, is the only true basis of geology ; and a trifling difference in the form of a shell, is deemed sufficient to constitute a new species, and to warrant the most important conclusions respecting the age of rock formations.

If the same conchologists were interrogated, respecting the power which the ancient inhabitant of the shell might possess, of changing its structure when placed in different circumstances, they would be compelled to confess their ignorance. A knowledge of fossil shells is highly useful to the geologist, in cases where the superposition of strata cannot be ascertained; but fossil shells alone, give us less positive information respect- X

PREFACE.

TO THE FOURTH EDITION. ing the ancient condition of the globe, than the organic remains of other classes of animals, or of vegetables ; because, for any thing we know to the contrary, all the species of molluscous animals that inhabited these shells, may have been capable of living in the same medium, and under the same conditions. But different species of vertebrated animals, and plants, must have existed under very different conditions, on land, or in water. M. Boue, an enlightened and indefatigable continental geologist, to whose labours the science is greatly indebted, is meritoriously endeavouring to resist the absurd attempt, to force Fossil Conchology into the chair of Geology. I trust his example will be followed by English geologists. Indeed, I am convinced that many of the frivolous distinctions introduced by conchologists will soon pass away, as those of mineralogy have already passed; and that these two branches of natural history, will take their proper stations, as auxiliaries subservient to geology.

It will be seen, by the titles to the new chapters in the present volume, that they comprise various subjects connected with important enquiries relating to the Theory of the Earth. The opinions of the author have not been rashly advanced, to oppose or maintain the systems of other geologists : they are the result of long-continued reflection, on what appeared to him the most probable explanations of geological phenomena. The author says probable, because he considers that the words truth and certainty, cannot yet be introduced with advantage into geological theories. The Third Edition of this work was republished in America, in 1829, by Professor Silliman of Yale College, Connecticut the distinguished editor of the American Journal of Science. It was commenced without any previous communication or acquaintance with the author.

The author will be satisfied if the present work should be thought deserving of the com mendation given by the American editor, of being " a com prehensive Treatise on Geology, which the student will be willing to read, and able to understand." Hanipstead, near London, April 18, 1833.

PREFACE.

TO THE THIRD EDITION. The First and Second Editions of the Introduction to Geology were favourably received, and 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 un necessary to mention : the delay has, I trust, been favourable to its appearance in a very improved 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 compared with the descriptions of former geologists.

I have also had opportunities of examining the collections, and of profiting by the communications, of some of the most eminent geologists on the Continent. While engaged in these pursuits, I have not been inatten tive 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 Geo logy has been recomposed, and all the chapters are greatly enlarged. The following new chapters have been added : — On Fossil Organic Remains. On the Principles of Stratification. A

PREFACE.

TO THE THIRD EDITION. Retrospective View of Geological Facts. On the Destruction of Mountains ; and on the Bones of Land Quadrupeds, found in Diluvial Depositions and in Caverns. On the Formation of Valleys; and on Deluges and Denudations. — The Plates are new, except Plate IV. and part of Plate VII. The Outline Map of the Geology 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 divisions of the country, without delineating the different strata in each divi sion. It was thought that the publication of this 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.

In the course of the present work, I have frequently at tempted to elucidate the geology of England, by comparisons with situations I have examined 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 observations 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. 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 £tre utile, sans atteindre a la perfection." Hampstead, near London, March 10, 1828. PREFACES TO THE FIRST AND SECOND EDITIONS, in 1813 and 1815, ABRIDGED.

In tracing the progress of knowledge, we may frequently ob serve that the cultivation of particular branches of science, at certain periods, was determined by causes which had little connection with their intrinsic utility. Fashion, caprice, and the authority of eminent names, govern mankind in philoso phy^ as well as on all other subjects. But, independently of accidental causes, thei-e are leading objects in the universe, which, as nations advance in civilisation, seem naturally to direct their attention to certain sciences in succession. The brilliancy of the sun, moon, and planets, their various 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.

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 ABimifiKLi I'KEDAPES TO THE elementary substances, of which all material objtCIS are etftn posed. In the order of succession, mineralogy and geologj are the last of the natural scicpcGS ; for though an acquaint ance with the earth \6 more important to mini, than a know ledge of the. distant parts of the universe, yet, previously to the cultivation of the other sciences, and of chemistry in par ticular, our knowledge of the mineral kingdom could not ex tend much beyond that of the rude*! 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 obserfBj that the most polished nation:, <>l antiquity had scarcely advanced beyond a limited acquaintance with astronomy, geometry, and mechanical philosophy. In modern Europe, all the natural sciences, geology and mineralogy excepted, have been successfully cultivated, and their progress has been astonishmgh rapid : but till about the middle nf the last century, the struc ture of the earth had scarcely engaged the attention uf philosophers. Near that time, Lehman, the German, first observed that there are certain rocks which occupy the lowest relative situation in different countries, and that these rocks contain no organic remains : hence be gave them the name of primary, and established a division between them and tho rocks by which they are covered, in which the remains of animals or vegetables frequently occur: tin: latter hi called secondary.

In our own country. tin; Ueverend J. Micholi was the first person who appears tu hau 1 had anv clear views respecting the structure of the external pints of tlie earth : they were made public in a valuable papri an the MftfSe of earthquakes, in the Philosophical Transactions, I7i9. About twenty yearafterwards, Mr. John Whitehur.-it published his " Inquiry into the original State and Fornmiiuu of the Kanh." His observations were principally confined to the rock* and strai.1 of 1 )erbyshire. Ii\di'pen<lintl\ ,>l its meculfttiVo mjj» ihhii:,, ilu wovl waa highlji Valimhl* r m mittnpl t<> dettrife FIRST AND SECOND EDITIONS. XV 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 in dustry and ability.

Mr. Whitehurst, however, fell into the same error with the celebrated Werner in Saxony, an error to which the first cultivators of geology were particularly ex posed, — that of drawing general conclusions from local ob servations, 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 century geological pur suits made little progress in England. On the continent, the researches of Saussure, Pallas, Werner, St. Fond, Dolo mieu, and others, had before this time produced a powerful interest, and brought into the field many active and en lightened enquirers. The first general impulse given to the public taste, for geological investigations 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 animosity and many ad ventitious circumstances were associated 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 plenti ful share of dullness, combined with a certain degree of tech nical precision, is regarded as essential proofs of profundity. By prescriptive right, long established in these realms, dull ness and pedantry guard the portals of the temple of Science, and command those who enter, to avert their eyes from what ever can elevate the imagination, or warm the heart, and to look at nature through a sheet of ice.

In compliance with their authority, writers of introductory treatises have gene rally thought it necessary to avoid that felicity in the familiar ABRIDGED PREFACES TO THE 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 introduc ing 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 enquiries: 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\Q\3.

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 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 common 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 inconvenience) omit the more rare crystallisations and varieties, so much valued by cabinet philosophers ; for here, as in many other instances, the received value is in an in verse ratio of the utility.

The pedantic nomenclature, and frivolous distinctions recently introduced into mineraloo-y, 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 mineralogists <nve to the same substance, and observing the avidity with which each new name is seized, as if it conveyed a hidden charm, FIRST AND SECOND EDITIONS. XVII 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 men of sense with the study of an important and interesting science; a science that has fol ks immediate 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 produc tions, subservient to the wants or enjoyments of man in civilised 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, adhi bebit ad considerandas res et tempus et diligentiam.) Alte rum est vitium, quod quidam nimis magnum studium multamque operam in res obscuras atque difficiles con ferunt, easdemque non necessarias." — Cic. Offic. i. 6. CONTENT S. Preliminary Observations on living Illustrations of Fossil Conchology, &c. - - - - Page xxxiii

Chapter I

Objects of the Science denominated Geology. — Definitions of Geology and Physical Geography. — The Shape and Density of the Earth. — Opinions respecting the internal Parts of the Globe. — Central Heat. — Temperature of the Earth. — 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 ; 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 of the Globe. — Remarkable Passage in the Institutes of Menu - - - - - 1 CHAP. II. on fossil, animal, and vegetarle remains, or paleontology.

Opinions of early Naturalists respecting Petrifactions. — On tlie Process called Petrifaction. — 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. — Fossil Elephant proved to have been an Inhabitant of cold Climates. — On Vegetable Petrifactions in the Transition, Secondary, and Tertiary Strata. — On the Progression from lower to higher Forms of Organic Structure 26 a XX CONTENTS. CHAP. 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. — Sedimentary Depositions. — Distinction between stratified -and stratiform Rocks.— Joints in Strata, called Slines and Cutters - - - - Page 48 CHAP. IV. ON STRATIFICATION, AND THE RELATIVE POSITION OF ROCKS. Strata and Geological Formations explained. — Various appearances presented by plane 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 Continuity of stratified Rocks broken by Valleys. — Longitudinal Valleys. — Transverse Valleys. — Lateral Valleys. — Denudations. — 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 Devastation in Alpine Districts. — On the Passages in the Alps called Cols ; and Observations respecting their Formation. — Different Ages of Mountain Ranges .... - 63 CHAP. V. ON ROCKS DENOMINATED PRIMARY, AND THE CHANGES TO WHICH THEY HAVE BEEN SUBJECTED.

The Origin of Rocks called Primary believed by many Geologists to be igneous. — A Classification founded on this View. A Classification independent of Theory. — Constituent Minerals of Granite. — Varieties of Granite. — Structure and Appearance of Granitic Mountains. — Mont Blanc, and the Aiguilles in its Vicinity. — Localities of Granite. — Granite Veins. Passage of Granite into Porphyry and Sienite. — Minerals found in Granite. — On Granite as the Foundation Rock on which other Rocks are laid. — The relative Antiquity of different Granitic Mountain Ranges. — Granite pierced through by Porphyry and Currents of Lava. — Granite sometimes protruded among the upper Strata - - . . - ° CONTENTS. XXI CHAP. VI. ON GNEISS AND MICA-SLATE, AND THE ROCKS WHICH ARE ASSOCIATED WITH THEM. On the Passage of Granite into Gneiss. — Gneiss and Granit veine. — Mica-Slate. — Formation of Gneiss and Mica-Slate — they are not stratified but stratiform. — Talcous Slate, and Chlorite Slate. — Chrystalline Limestone, denominated Primary, occurs both in Primary and Secondary Mountains. — Formation of Limestone and Coral Islands by Animal Secretion. — Dolomite, or Alpine Magnesian Limestone. — Serpentine and Ollite, or Potstone. — Euphotide or Saussurite, the hardest and heaviest of Rocks. — Trap Rocks changed to Serpentine. — Eurite or White Stone Primary Porphyry a Mode of Granite. — Recurrence of the same Rocks in Rock Formations of different Epochs - - - ...

Page 108 CHAP. VII. ON TRANSITION ROCKS, AND ON THE PROBABLE CONDITION OF THE SURFACE OF OUR PLANET DURING THE TRANSITION EPOCH. Transition Rocks intermediate between the Primary and Secondary. — Their Characters. — Slate or Clay Slate. — Peculiarities of Structure. — Varieties of Slate. — Greywacke and Greywacke Slate. — Passage of, into Red Sandstone and Gritstone. — Conglomerate and sedimentary Transition Beds intermixed with Trap Rocks. — Lower Transition Limestone ; Contortions of, and remarkable Position of its Beds. — Upper Transition or Mountain Limestone contains Beds of Magnesian Limestone. — Errors respecting the Mountain Limestone of Derbyshire. — Changes and Anomalies in the Stratification of Mountain Limestone. — Structure of Crich Cliff. — Quartz Rock, Jasper, Greenstone. — On conformable and unconformable igneous Rocks intermixed with Transition Rocks. — Transition Series of Cumberland and Yorkshire, different from those of Shropshire and Wales, called Silurian Rocks. — Thickness and Extent of the Silurian Beds. — On the Temperature of the Globe and the Animals of the Transition Epoch - - - 126 CHAP. VIII.

ON THE LOWER OR GREAT COAL FORMATION. The Geological Position and Structure of Coal Districts, called Coal-Fields. — Dislocation and Disturbances of Coal Strata by Faults and Dykes. — Mineral Coal, Anthracite, Plumbago, Wood- Coal, or Lignite. — Iron-Stone accompanying Coal Strata. — On Carbon as an original Constituent Part of the Globe. — On the Origin of Coal Strata, and their Deposition in fresh-water a CONTENTS. Lakes or Marshes. — Numerous Repetitions of the same Series of Beds in the same Coal Field. — Precautions necessary in the Establishment of Iron Furnaces. — On the Mode ot searching for Coal. — Hints to landed Proprietors on the Probability of finding Coal in Districts where it has not yet been discovered.— On the Formation of Coal-Beds in Fresh-Water Lakes. — On the Conversion of Vegetable Matter into Coal.— Imperfect Coal Formations. — Salt Springs in Coal Strata. — Coal Mines in France and North America. — Observations on the Consumption of Coal in England, and the Period when the Coal-Beds will be exhausted. — Additional Remarks on the same Subject. — Sec tion of the Coal Strata at Ashby Wolds - - Page 159 CHAP. IX.