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. Second edition, considerably enlarged

Introduction

TO GEOLOGY, ILLUSTRATIVE OF THE GENERAL STRUCTURE OFTHE EARTH; COMPRISING THE ELEMENTS OF THE SCIENCE, AND AN OUTLINE OF THE GEOLOGY AND MINERAL GEOGRAPHY OF ENGLAND: By ROBERT BAKEWELL. THE'SECOiSD EDITION CONSIDERABLY ENLARGED. •' A knowledge of our subterranean wealth would be the means of furnishing greater opulence to the country than the acquisition of the mines ,,f Mexico and Peru." President of the Board of Agriculture. LONDON : PRINTED FOR J. HARDING, 36, ST. JAMBS _ STREET. 1815. ' 1 — - — <— — — -_.____._>_»,. Printed by Richard ani Arthur Taylor , Shoe-Lane, /,«_* THE FIRST EDITION. In tracing the progress of knowledge, we may frequently observe that the cultivation of particular branches of science at certain periods was de termined 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 na tions advance in civilization, 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 en dowed with life and intelligence, and attributed to them a mysterious power over human affairs : thus the heavenly orbs became the objects 01 religious adoration ; and curiosity, hope, and fear, lent their aid to the early cultivation of astronomy. Mathematics and mechanical philosophy are A 2 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 ele^ mentary 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 cultivation of the other sciences, and of Chemistry in particular, 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, THE FIRST EDITION. V sciences, geology and mineralogy excepted, havq 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 latter he called secondary.

In our own country, the Reverend J. Michell was the first person who appears 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 Trans actions, 17.59. 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, ceneral accuracy, will remain a lasting momimenc of VI

Preface

TO of the writer's industry and ability. Mr. White hurst, however, fell into the same error with the celebrated Werner in Saxony, an error to which the first cultivators of geology were particularly exposed, 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 century geological pursuits made little progress in England. On the continent, the researches of Saussure, 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 investigations in this country was produced by Professor Playfair*s luminous and eloquent illustra tions 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 ably and very warmly op posed ; 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. The interest excited by the brilliant discoveries lately THE FIRST EDITION. VII lately made in chemistry has accelerated the pro gress of geology, by developing new views respecting the objects in the mineral kingdom, and cre ating a desire to be acquainted with the situations in which they occur. Hence a taste for such in quiries is more prevalent among the intelligent classes of society in this country than at any former period ; and in the course of my professional pur suits, and the geological lectures I have occasion ally delivered, I have repeatedly heard the want of an intelligible introductory treatise on geology much regretted, by persons who lamented their inability to comprehend the ' Geognosy' of Mr. Jameson, and their equal inaptitude of attention to the polemical controversies of M. De Luc.

To both these gentlemen geology is under considerable obligations ; and if their elementary works have failed in exciting general interest, it is owing, I conceive, to an over-strained attachment to their particular theories, or to the technical obscurity irj which those theories are involved #. He * Mr. Kirwan may be justly regarded as the father of British Mineralogy : but he appears never to have studied geology out of his own cabinet ; for though Dublin, where he resided, is more favourably situated for geological in quiries than perhaps any other capital in Europe, he con sidered the interesting rock formations in its vicinity as ob jects far too sacred to be explored, except by German eyes. The Dublin Society, in conformity with his example, have recently

PREFACE.

TO He who attempts to make a scientific subject familiar, runs the risque in this country of being deemed superficial : a plentiful share of dullness, combined with a certain degree of technical precision, are regarded as essential proofs of profundity. By prescriptive right long established in these realms, dullness and pedantry guard the portals 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 compliance 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 va rious parts of our island, with the drawings, sections, and map in the present volume, will I trust facilitate the study of geology, and prove parrecently elected a German Mineralogist for the avowed purpose of delivering public lectures on Geology, disregard ing the trifling inconvenience of his being an utter stranger to the English or Irish languages. ticularlv THE FIRST EDITION. IX ticularly 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 his tory of England, will secure it a candid reception. 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.

The number of simple minerals which form rocks and strata is small ; and when the student is well acquainted with their physical and chemical proper-* ties, their external characters, and more common modes of intermixture and combination, he is prepared to commence an examination of nature for himself with satisfaction and advantage. The pedantic nomenclature and frivolous distinctions recently 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 minera logists 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

PREFACE.

TO THE FIRST EDITION. X ,«t 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 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 par ticularly 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 unpro fitable subjects.' ' In hoc genere et naturali et ho nesto duo vitia vitanda sunt : unum, ne incognita pro cognitis habeamus, hisque temere assentiamur (quod yitium effugere qui volet adhibebit ad con siderandas res et tempus et diligentiam).

PREFACE.

TO THE SECOND EDITION. -T ROM the speedy sale of the first edition of the Introduction to Geology without any assistance from the patronage or early notice of the literary journals and reviews, it may be presumed that the work was favourably received. I am therefore en couraged to publish a second enlarged edition under circumstances, in some respects, more favourable to its success. A person unconnected with public societies, whose name is undecorated with any appendages, has certain difficulties to encounter when he first presents a book on any science to the world. Many even of the learned vulgar, whose minds, as Locke* expresses it, are " confined in a little Goshen of their own," are very unwilling to believe that any knowledge or information can exist beyond the precincts of those establishments or societies with which they are acquainted.

The following incident may illustrate the truth of this remark. Soon after the appearance of the first edition, a gentleman * Conduct of the Human Understanding. placed placed the book in the hand of a learned and reverend professor in one of our English Universities, accompanied with the inquiry, ' Have you seen this book, sir?' — ' Yes, I have.' — ' Pray what do you think of it?" — ' G — d ! I don't know, but I wonder where the devil he got his information !' was the reply. Though the answer may sound unclerical to English ears, I am willing to believe that it is conformable to the legitimate modes of figurative expression and the strictest rules of poetical propriety, — rules with which this reverend professor is of course so familiar. Men of more enlarged minds are ever ready to hail the progress of information, without stopping to -inquire whether it be given by a titled or untitled individual.

A distinguished ornament of the other university, a prelate whose name will long be dear to science, to learning, and religion, the venerable bishop of Landaff, rose, as he expressed it, immediately from the reading of my book to lose no time in communicating his approbation to the author, a testimony the more flattering, as it was given without any previous communication or acquaintance with his lordship ; and still more gratifying, as it was from the early perusal of his lordship's Chemical Essays that I first acquired a taste for these pursuits. These essays, amidst the changing language of theory, will ever remain a valuable record of facts, and serve as a perfect model for a just philosophical style ; learned without without pedantry, definite without technical obscu rity, at once simple, elegant, and perspicuous.

To return to my professor : Should he honour the present edition with his perusal, I trust he will find in it additional information, and that he may not again invoke supernatural agency to reveal the means by which it was acquired, the case being hand dignus vindice nodus, not of sufficient diffi culty to require such assistance ; I shall briefly acquaint him with the secret. Since the first appearance of the work, I have travelled over two thousand miles of the United Kingdom, and had an opportunity of revisiting some of the districts before described, and of examining others I had not then seen. I have also taken a short view of the rock-formations in the west of Anglesea, and the opposite coast of Ireland. From gentlemen residing in the country, who had perused the book, I have received some information and corrections, and I have not been inattentive to the more im portant observations and discoveries of other geologists in our country or on the continent.

In the present edition I have ventured to advance some opinions respecting the process of rock-formations, which I am inclined to flatter myself will show that various apparently contradictory or anomalous facts are referable to one general cause, and that some of the difficulties under which geology has hitherto laboured, admit of a satisfactory explanation. planation. These speculations being proposed as queries, and their truth or probability submitted to their accordance with existing appearances on the surface of our planet, I trust they will be received with indulgence. In an introductory work, the entire departure from language hitherto received by geologists would be attended with much inconvenience ; I have therefore retained the terms primary, transition, &c. though I am convinced that recent observations show more and more their impropriety, when taken in their strict original sense.

If, however, by primary countries we mean to designate those in which granite, gneiss, and mica-slate predominate, without any reference to theory; and by transition countries, those abounding in metalliferous lime stone or in rocks allied to slate, the terms can occa sion no error, and we thereby avoid prolixity of de scription. The great mistake was in fixing these terms as the expression of invariable natural characters, and in asserting that the same succession of rocks that occurs in Saxony, which Werner first described, exists, or once existed, in every part of the world. Since the universal evidence of facts in other countries made the Wernerian arrangement no longer tenable, there has been such shuffling and shifting of rocks from one class to another, that it threatened to upset the whole surface of the globe, to the no small terror of its inhabitants. habitants, had they been apprised of the danger.

A disciple of Werner has lately ventured to anticipate that the Professor may find it con venient to let some of his universal formations 'slip out of his system.' For the consolation of the timid, we may venture to predict, that when these universal rock-formations pass away, the shock will occasion no catastrophe to our planet, as they never had any existence in nature. The advocates of this system, instead of acknowledging the funda mental error of the first arrangement, imitate the physician of Moliere, who placed the heart of his patient on the right side and the liver on the left, and when reminded by the father that the reverse was believed to be the fact, replied, ' Ah! oui, c'Stoit ainsi autrefois, mais aujourÆhui nous avons change tout cela. — " It used to be so formerly, but at present we have changed all that*."

If philosophers would turn their eyes more upon nature, and think less of artificial classifications, they might not de scribe their observations with such a technical parade of knowledge, but they would mark more distinc _v those natural characters and circumstances that escape the eyes of common observers, but which lead directly to the most valuable discoveries. It has been urged as an objection to the cultivation of geology, that the phænomena of which it proposes to treat, lead us back for their explana- * Le Medecin malgre lui. tions

PREFACE.

TO tions to periods of time of which we have no historic records; and the objects of present research being buried under the surface, our conclusions are obscured by uncertainty. Objections of equal validity might be advanced against all the other sciences. In chemistry, the very existence of its most important agent caloric, or heat, as a specific substance, is denied by some very eminent philosophers ; nor have we, perhaps, better evidence for the existence of oxygen, azote, or hydrogen, as simple elementary substances. In mechanics, the important question of the ratio between the velocity and momentum is still undecided. Even in pure mathematics, where the light of truth is supposed to shine with unclouded splendour, some of the very first definitions are exposed to objections which the most vigorous minds have not been able to remove, and demonstrations of elementary propositions admitted by mathematicians for two thousand years, are now found to be defective or erroneous*.

The more abstract speculations on space, time, and matter, have engaged and exhausted the highest intellects of ancient and modern times ; yet the mysterious veil is still unremoved, and the only benefit resulting from these inquiries has been to exercise, and in some degree to fix limits to, the powers of the human mind. Are we hence to neg- * See Playfair's Geometry, notes on book vii. prop. 20 ; and Simpson's Euclid, notes on book x '. des. 10. lect leet the cultivation of science ? Because we cannot always bask in the blaze of meridian day, shall we close our eyes and sit in darkness indulging " a sul lenness against nature ? " There are, indeed, few subjects on which we can acquire demonstrative proof; yet our faculties are so constituted, in rela tion to external objects, that we are able to obtain a high degree of probability sufficient for all useful purposes.

The geologist cannot lay open the internal structure of the globe, nor penetrate very far beneath its surface ; but what is within his reach is sufficiently interesting and valuable to arrest our profound attention. In the short space of time that geology has been cultivated, perhaps no science was ever more rich in astonishing discove ries ; discoveries which have opened the volume of Nature, where the history of the primæval inhabitants of the globe is imprinted in legible charac ters. I have spoken elsewhere of the immediate utility of geological researches, as disclosing the various treasures of the mineral kingdom. At a time when it becomes so necessary that we should avail ourselves of our natural resources, a work which proposes more immediately to direct the at tention of my countrymen to the mineral repositories of Great Britain may claim their indulgence and patronage. The difficulties which have been un necessarily created in mineralogy and geology, by multiplying names to designate the same mineral b substance,

PREFACE.

TO substance, and by frivolous subdivisions of species, have more than any other cause retarded the pro gress of these sciences. Unfortunately, books alone cannot make the student acquainted with minerals : they may teach him what a substance is not ; but they will seldom enable him to say what it is, unless he be previously familiarized with specimens. The external characters of minerals are some times too evanescent to be fixed by language, and it is only by frequent inspection that the eye can be habituated to detect them : hence this kind of know ledge is in some degree empirical, and hence may arise that kind of pedantic conceit said to charac terize many who think themselves accomplished mineralogists. It might serve to abate this supercilious self-complacency, were it more generally known that the knowledge on which it is founded, requires less comprehension of mind, and less labour of thought, than are necessary for the attainment of the humblest mechanic art.

A steady eye and free access to well-arranged mineral collections are all the requisites for forming an expert mineralogist, whatever may be the range of his intellectual jiowers. In making these observations I by no means wish to undervalue mineralogy ; the knowledge of it is absolutely necessary to the geologist, and highly useful for various purposes of life ; but it is not the less useful for being easy of attainment. I object to what _\ hat Sir Humphry Davy (in his Lectures) very pro perly ca _ed "barricading the avenues to knowledge from general access by a fortification of hard words and frivolous distinctions." In no department of science has this sin against good taste been so frequently and remorselessly committed, as in that of mineralogy. Crystallography more properly belongs to the higher branches of physics : the laws of crystal lization, explained by the ingenious labours of De Lille and Hauy, have enlarged our views of some of the more refined operations of nature, and have disclosed a marvellous system of geometrical arrangement, extending to the minutest particles of matter, not less regular than the laws which govern the planetary motions.

The practical mineralogist can, however, rarely apply the angular measurement of crystals to the examination of minerals in na ture, because few of them comparatively are found in a perfect crystalline state. He who would gain a useful knowledge of mi neralogy, would do well to provide himself with specimens of simple minerals and of the different common rocks, 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 crystallizations and varietiesso much valued by cabinet philosophers: for here, as in many other b 2 . instances,

PREFACE.

TO XX instances, the received value is in an inverse ratio to the utility. Considering the great benefits which mankind in civilised society receive from the mine ral kingdom, it is truly astonishing that so little at tention has been paid to mineralogy or geology until nearly the present time. It is not my inten tion to dwell on the advantages to be derived from the practical application of these sciences to the im provement of landed property, I beg leave to re fer to the notice on this subject, page 454. The value of every science must ultimately rest on its utility; but in making the estimate we ought not to be guided alone by the narrow views of immediate gain. The objects of nature appear destined to answer two purposes ; the one, to supply the physical wants of the various inhabitants of the globe; and the other, to excite our curiosity, and stimulate our intellectual powers to the discovery of those laws by which all the successive changes in the material universe are governed.

Were it not for this intellectual excitement, man would be little advanced above the beasts of the forest. In those sciences which have reached the greatest perfection, the contrivance of the Divin . Artist, and the ends and uses of the various parts, are most apparent. Geology has not yet made sufficient progress to carry us far in this path of inquiry ; but we can already discover that the very disorder in which the surface of the globe is apparently thrown, and the inequalities which it presents, are absoabsolutely necessary to its habitable condition :-- the distribution of its mineral treasures, particularly of coal to the colder regions of the globe, is also well deserving our attention ; but a cold-hearted philoso phy, under the sanction of a quaint expression of Lord Bacon *, has (to use the wordsof Dugald Stew art)" made it fashionable to omit the consideration cf final causes entirely, as inconsistent with the ac knowledged rules of sound philosophising.

The effect of this has been to divest the study of nature of its most attractive charms, and to sacrifice to a false idea of logical rigour all the moral impressions and pleasures which physical knowledge is fitted to yield." * The sentence which condemns the inquiry after final causes as a barren study, is one of those puerile witticisms so common with the writers of Lord Bacon's time, and would have been deemed unworthy of notice had it occurred in the works of any of his cotemporaries. . Causarum finalium inquisitio sterilis est, et tanquam virgo Deo consecrata nihil park." CONTENTS.

Chapter 1

Objects of the science denominated Geology. — The shape ns the earth and other planets affected by the respective velocities of their rotatory motions. — Density of the earth. — Theoretical division and classification of rocks. — Arrangement of the mineral districts of England. — The present continents once covered by the ocean : existing proofs of this on many of the highest mountains in England, Spain, South America, and various parts of the world — Fossil remains of marine animals, vegetables, and quadrupeds. — Strata in which they are imbedded, formed in succession at different periods. — Human skeleton in a calcareous rock at Guadaloupe.— Inferences respecting the former condition of the globe. i

Chapter II. On The Structure And Composition Of Rocks

Terms employed in Geology. — Rocks Simple or Compound : Varieties of their internal structure. — External structure of Mountain Masses : — Indeterminate, Stratified, Columnar, Tabular, and Globular: — the three latter the effects of crystalli7ation en masse. — Tabular Structuie erroneously confounded with the Stratified. — Elementary Substances. — Minerals of which Simple and Compound rocks are principally formed. - - _ 24

Chapter III. On The Position And Arrangement Of Rocks

AN3 STRATA. Different positions explained.— Relative ages of rocks determined in some instances by their position, and by the substances CONTENTS. XXIII stances imbedded in them. — Appearances presented by stratified parallel rocks, illustrated by a section of the country from Sheffield to Castleton. — Excavation of Valleys. — Valleys formed by the dislocation of Rocks and Strata. — Beds of Gravel: opinions respecting their formation. — Transportation of blocks of granite to distant countries, how effected. Bones of large quadrupeds transported without injury by similar operations. — Hills and Mountains, observations respecting their declivities. . — — - — 45

Chapter IV. On Granite And Other Rocks Denominated Pri- Mary

Geological Classification of Rocks: — 1. Primary — 2. Indeterminate or transition rocks — 3. Basaltic— 4. Upper secondary — 5. Alluvial — 6. Volcanic — ". Fresh water formations. — Granite rocks, their composition and structure. — Granitic mountains of Europe and America. — Mont Blanc. — Granite "Veins. — Situation of Granite Rocks in England Rocks of Gneiss and Micaceous Schist described — Micaceous Schist of Anglesea and the opposite coast of Ireland. — Crystalline lime-stone in Primary Mountains. — Formation of Lime by animal secretion. — Origin of calcareous rocks. — Serpentine Rock. — Verd antique — Beautiful Serpentine of Anglesea. — Quartz Rock. — Anomalous Rocks. — 5y

Chapter V

£N SLATE AND OTHER TRANSITION OR LOWER SECON- DARY ROCKS. Hocks of this class contain certain organic remains — are commonly metalliferous — Argillaceous Schistus or Slate. — Varieties o! Slate. — Gray-wacke. — Metalliferous Lime stone. — Extensive caverns in this Lime-stone. — Amygdaloid of Derbyshire. — Opinions respecting its formation. — General view of Primary and Transition Mountains. - 100 CHAP- CONTENTS. XXIV

Chapter VI. Basaltic Rocks, Porphyry, And Sienite

Position of these rocks, their gradation into each other, and resemblance to volcanic products — Sienite, Green. stone, Basalt, Amygdaloid, and Porphyry described. — Neglect of Porphyry by modern architects. — Various formations of Porphyry. — Columnar and Globular Basalt. — Experiments illustrating their formation — Basaltic Rocks of Auvergne and Sicily. — Basaltic Columns of Ireland and the Scotch Hebrides. — Basaltic Rocks extending in the same parallel of longitude. — Speculations of different Geologists. — Theory of Werner. — Observations of Sir G. Mackenzie in Iceland.— Remarkable appearance of Basalt at the Clee Hills in Shropshire and in the county of Durham, illustrating the origin of Basalt. —^Basaltic Columns of Teesdale. - - 115