Geology for all, etc

Front matter

JOHN MORRIS; M.A., Cantab.; F.G.S.; Hon. Memb. Geol. Assoc. ; For. Memb. Roy. and Imp Geol. Inst., Vienna; Nat. Hist. Soc, Dresden ; Acad. of Nat. Science, Philadelphia ; Soc. G6ol. du Nord. Goldsmid Professor of Geology and Emeritus Professor, University College, London; Deputy Woodwardian Professor of Geology in the University of Cambridge ; First Lyell Medallist ofthe Geological Society ; Twice President of the Geologists' Association. Boro.1810; Died 1886. A GENERAL CONSPECTUS OF THE SUBJECT ADAPTED FOR ALL INTELLIGENT READERS. BY J. LOGAN LOBLEY F.G.S., etc., PROFESSOR OF PHYSIOGRAPHY, CIT7CTF LONDON COLLEGE; FORMERLY HONORARY SECRETARY, ORGANIZER OF FIELD MEETINGS AND EDITOR OF ' PROCEEDINGS ' OF THE GEOLOGISTS* ASSOCIATION, HONORARY LECTURER ON GEOLOGY, WORKING MEN*S COLLEGE, ETC, ETC. ; AUTHOR OF "MOUNT VESUVIUS,' ' THE STUDY OF GEOLOGY,' "DISTRIBUTION OF BRITISH FOSSIL BRACHIOPODA,' ETC, ETC.

LONDON: ROPER & DROWLEY, 2g, LUDGATE HILL 1888. I to THE MEMORY OF MY GREAT MASTER, JOHN MORRIS, AN ENTHUSIASTIC GEOLOGIST, A LEARNED PROFESSOR, A LUCID EXPOSITOR, A GENIAL COMPANION, A FIRM FRIEND, AND A MODEST MAN, 3 "Dcbicote tl)is "28oofe. For the Portrait of Prof. Morris the Author is indebted to the courtesy of Dr. Henry Woodward, F.R.S., the Editor of the Geological Magazine, in which, together with a Memoir of the Pro fessor, it originally appeared in November, 1878 (New Series, Decade II., vol. v., p. 481). PACK Vll 17 14 CONTENTS. Prefatory

Chapter I. Introductory

Object and Scope of Geology — Value and Advantages of Geological Knowledge — Recent Development of the Science — The Principle of Geological Investigation — Schools of Geological Opinion -

Chapter II. Agencies Affecting The Exterior Shell Of The Globe

— INORGANIC. Atmospheric and Thermal — Aqueous — Glacial — Volcanic — Seismic — Upheaval and Subsidence - - -

Chapter III. Agencies Affecting The Exterior Of The Globe

— ORGANIC. Effects of Vegetable Life — Destructive Action — Constructive Action — Preservative Action — Effects of Animal Life — Accumulations of Shells and Bones — Oceanic I — CONTENTS. IV A,. I Ooze — Sponge Spicules — Coral Reefs and Islands — Theories ofthe Formation ofAtolls— Geological Influence of Man ------- 3'

Chapter IX. Rock Masses

Stratification — Lamination — Foliation — Dip — Strike — Outcrop — Anticlinal Axis — Synclinal Axis — Joints — Contortion — Faults — Unconformability— False Bedding — Overlap — Escarpments — Outliers — Inliers — Dykes — Veins — Lodes — Mineral Beds -

Chapter XV. Stratigraphical

GEOLOGY— CAINOZOIC. The Cainozoic Rocks — The Eocene — The Miocene — The Pliocene — The Glacial Epoch — The Post Pliocene — Distribution of Types in Time — Continuity and Development of Organic Nature - - - - 119

Chapter XVI. Topographical Geology Of The British Islands

Igneous and Metamorphic Areas — General Position ofthe Aqueous Rocks of England and Wales — Cambrian Areas — Silurian Areas — Devonian Areas — Carboniferous Areas — Permian Areas — Triassic Areas— Jurassic Areas — Cretaceous Areas — Tertiary Areas — Facilities for Geological Study in Great Britain 127

Chapter XVII

Orological Geology. The Mountain Skeletons of Continents — European Mountains— Asiatic Mountains— African Mountains- American Mountains 135 Principal Rock-Forming Minerals 148 Table of the British Aqueous, Sedimentary, or Stratified Rocks - 149 Approximate Maximum Thicknesses of British Strata ------- 150 Index 15- PREFATORY. The matter contained in the following pages — the substance of a Course of Lectures delivered at the City of London College, in Michaelmas term, 1 887 — ap peared in a series of articles written for the Industrial Review ; but a desire having been expressed for their re-publication, they are here collected, with some requisite expansions and additions. The little work so produced is intended, and it is hoped adapted, for the general reader who does not desire, or is not prepared to undertake the acquirement of, that amount of chemical, mineralogical, and palæon tological learning required by an academic study of geology.

The great teachings of the science — and great indeed they are — are neither dependent upon petrological minutiæ, the specific or even the generic differences of fossil forms, nor upon a detailed know ledge of each formation or group of strata. Text books of geology necessarily bristle with the unfamiliar names of fossils, standing out forbiddingly in italics, and contain so many tables, sections, and lists, that to ordinary readers they are rather deterring than attrac tive. It is doubtless true that not a few works of great value have been written to diffuse geological PREFATORY. knowledge, in which these deterring features are not present, but in some of these the subject has been dealt with in a partial or fragmentary manner, portions thought to be specially attractive having been selected for elucidation, and others have been intended rather for the commencing student than for the ordinary reader.

Accordingly, while in these pages a severely classificatory arrangement, with tables, lists, sections, and unnecessary scientific terminology, has been avoided, the important facts and deductions of the whole subject have been presented with perhaps sufficient system and method for clearness, and suffi cient fulness for a satisfactory statement. The un broken narrative may induce the reader to continue the perusal, and so absorb important facts with ease ; when, should his interest in the subject be so far stimulated as to cause him to desire a more intimate and detailed knowledge, he will seek the aid of one of the excellent text-books that have been published during the last ten years. Thus, while ' Geology for All ' may be sufficient for those requiring only a general knowledge of the subject, it may serve as an introduction to a more complete study for others.

The absence of geological teaching in the ordinary schools of the country is doubtless due to several causes, but one of them may be an impression that a sufficient knowledge of geology is difficult to acquire on the part of the schoolmaster, and the subject too recondite for the pupils. These pages, it is hoped, will show that anyone of ordinary intelligence may easily master the principles and the important facts of the science, while its teachings are of such a PREFATORY. IX generally and usefully instructive character as to be eminently fitted to improve the education of youthful minds. But perhaps the great cause of the absence of geological teaching is the example set by the two chief Universities of Great Britain. For although Chairs of Geology are established at Oxford and Cambridge, no geology or knowledge of what are called the Natural Sciences is required for the ordinary pass degree, so that a graduate of either of our two ancient seats of learning may leave his Alma Mater even with honours, and yet be without an acquaintance with any of these sciences.

The consequence of this is that the great Public Schools devote their attention to those subjects which are required to fit their boys for obtaining, when at the Universities, the pass degree. The practice and curricula of the Public Schools again are necessarily followed by the preparatory schools, and the standard of education so set up and made fashion able dominates the teaching of schools generally. Hence it is, in a great measure, that in England education in science is so far behind that of Germany, and we look in vain for geology in the curriculum of an ordinary middle-class school, or for a schoolboy who can tell how the slate he uses was formed, or of what it is composed. It is to be hoped, however, that enlightened public opinion will before long induce the governing bodies of the Universities to require a certain amount of acquaintance with natural science from every candidate for a degree.

The time will then not be far distant when the schools of Great Britain generally will introduce into their PREFA TOR Y. X courses of instruction the rudiments at least of both Physical Geography and Geology. The Government, too, might do much by means of its colleges — Woolwich, Sandhurst, and the Staff College — and still more by making Elementary Geology an obligatory subject in all examinations, whether for the Civil or the Naval and Military Services. Fitness for any specific employment is sometimes more effectually promoted by that which draws out, e-duces, the mental powers, and so truly educates, than by the burdening the mind with empirical or statistical information which can be easily acquired by a well-developed intellect to the extent found to be necessary when required for actual use.

Nor is geology better known amongst the elder generation. Indeed, it is rare to meet anyone outside geological circles who knows anything of the science, and references to geological facts in the press frequently show a want of acquaintance with even its rudiments. The Geological Society and the Geologists' Association publish lists of their Fellows and Members, showing those in each county ; and thus it is possible to ascertain approximately the number of the inhabitants having a good knowledge and a love of geology ; for it may be assumed that in England most geologists belong to either one or other of these societies. From these lists it is found that in a population of 5,874,174* only 157 are Fellows or Members of either of the two Metropolitan bodies, 0 Population of the six representative counties, Bedfordshire, Devonshire, Gloucestershire, Lancashire, Suffolk and Warwick shire.

PREFATORY. XI and even doubling this number will only give I geologist to 18,707 of the inhabitants, or 1 to 3741 of adult males. This lack of knowledge of the structure of the earth on which we live, of the history of its formation, and of the causes of those beautiful features which diversify the surface, give pleasure to the cultivated mind, and in a great measure determine the extent, and the productions, and the character of the nations of the world, appears most deplorable and urgently requiring attention. But the experience of twent}' years has shown me the difficulty of arousing anxiety about it even in scientific circles. Some years since a gold medal was offered to the governing body of a society whose raison d'etre is the diffusion of scientific knowledge, as a prize for geology, to be competed for by pupils of Middle Class Schools ; but such reluct ance to accept it was shown, when the reverse was expected, that the offer was withdrawn.

Thus what was calculated and intended to be even of national importance — for the example would doubtless have been followed — as well as of benefit to the power and influence of the society, was frustrated, and nothing has yet been done to introduce the teaching of geology into the ordinary schools of England. That there is not greater propagandist zeal amongst scientific men is in some measure due, doubtless, to the fact that many are to a considerable extent specialists, a devotion to one department of a science being, perhaps, calculated to repress enthusiasm for disseminating the broad teachings of the whole. Many, too, are so engaged professionally that they PREFA TOR Y. have little time for proclaiming to the world what it is their duty to teach to their students. Still there is much truth in the opinion lately expressed by Sir James Paget, at the Mansion House, that if scientific men had more enterprise, much more good would result to mankind from their researches.

The great chartered body of geologists, the Geological Society, with ample resources and great power and influence, does not deem it to be its duty to propagate amongst those outside its own limited circle a knowledge of the science in the interests of which it exists ; but considers that it is best fulfilling its mission, and carrying out most completely the objects and work prescribed by its Royal Charter, when it devotes all its power and influence to, and gives all its honours and rewards for, the advance of geology. The teachings of the facts of geological investigation already known are so important, that their diffusion seems to be at least as beneficent a work for the world as the further accumulation of details of the same character as those on which these great teachings are based, however valuable such research may be.

It would therefore seem to be a matter for regret that the Geological Society is not able to devote a little of its means and some of its influence to the spreading abroad of a general knowledge of the science ; to do, in short, for geology what the Royal Geographical Society does for geography. But what the senior and greater society does not do is done to some extent by the junior and lesser society, the Geologists' Association. This body, PREFATORY. XIII with a small subscription, and therefore limited means, and without great power or influence, does a large amount of educational and propagandist work, and has so developed and perfected its field meetings that they are models for the imitation of other field societies ; and their success has suggested and been the cause of the formation of not only new geological field societies, but also of new general Natural History societies in counties where geologists are too few to constitute a society themselves.

But even the Geologists' Association does not do all that could be done, for it might be made a still greater educational power by the employment of new methods calculated to further increase its usefulness. Yet another body, the Society of Amateur Geologists, has recently been founded in London, including amongst its members some young men of great earnestness and ability, who, it is to be hoped, untrammelled by restrictive traditions or any spirit of exclusiveness, will earnestly aim at the diffusion of geological knowledge as widely as possible. Young geologists, it seems to me, should not only wish to increase their own knowledge, but have a strong desire to benefit the world by imparting it to others, and so be imitators of those illustrious fathers of their science, Hutton, Smith, Buckland, Sedgwick, Murchison, Lyell, Phillips, and Morris.

The two capital cities of Dublin and Edinburgh possess geological societies which, like that of London, have done most excellent work for the advance of geological science ; and they may in the future be able to do more than in the past for its PREFATORY. XIV dissemination. In some of the larger provincial cities and towns there are also geological societies ; in Liverpool there are even two ; and these, though necessarily small bodies, have been of great service, if not in largely increasing the number of geologists, at least in promoting a thorough investigation of the strata of important districts. The Manchester and the Dudley societies have valuable museums, and the field-meetings of the latter body are methodically organized and of a highly practical and useful character. But no one who calls attention to the means for diffusing geological knowledge ought to omit to mention the many Natural History Field Societies- County and other — which, following the good ex ample long ago set by that pioneer of Field Societies, the Woolhope Club, include geology in their range of subjects, and occasionally devote a meeting, either wholly or in part, to the observation of the geological structure of their respective neighbourhoods, by which their members generally are enabled to obtain some acquaintance with the rocks and their teachings.

Some of these societies possess admirable local geological museums, open to the public, which to a great extent take the place in provincial towns of the National Museums in London, and so exhibit to all the long-buried ' Medals of Creation.' Geological Museums are well calculated to awaken curiosity and excite interest, if their contents are well and simply arranged, and, above all, conspicuously and simply, but copiously labelled. Nothing engages the attention of the unscientific visitor to a museum so PREFA TOR Y. XV much as familiar names, especially if they are in combination with a clear, terse, and brief statement that will both interest and instruct. During the last thirty years a very marked advance has been made in the manner of displaying the contents of local museums, while the great museums in London, in the arrangement and display of their specimens, leave little to be desired.

The Museum of the Royal College of Surgeons, which, though not a national one, is very generously opened to the public, is an excellent one for the teaching of palæontology, typical examples illustra tive of all the classes of the Animal Kingdom being prominently displayed. The Museum of Practical Geology in Jermyn Street ought to be much more widely known, and much more visited than it is, for the arrangement is so good, the specimens, models, etc., so attractive and illustrative, and the whole so compact and accessible, that it appears almost a model of what such a museum should be. Further west, that noble Palace of Science, the new Natural History Museum, must be visited by every geologist with pleasure and pride, for nowhere else in the world is there such a collection of fossils and minerals so splendidly displayed, so sumptuously mounted, and so grandly housed ; but the very great ness and richness of the geological feast here spread out produces the keener regret that so large a number of the population have not the elementary knowledge of geology requisite for its due apprecia tion and enjoyment.

PREFA TOR Y. XVI From a conviction of the great educational value of geological knowledge, it has been the great pleasure and the chief work of my life to diffuse it more widely ; and in the same spirit this book is given to the public. I am fully conscious of the many defi ciencies of a restricted plan ; but if it be in any degree instrumental in widening the circle of those who know and appreciate the great facts of geology, and possess an acquaintance with the far-reaching and enlightening teaching of the records of the rocks, this little volume will be a source of the greatest gratification to its Author. J. L. L. City of London College, March, 1888.

Chapter I. Introductory

Object and Scope of Geology — Value and Advantages of Geological Knowledge — Recent Development of the Science — The Principle of Geological Investigation — Schools of Geological Opinion — Method of Inquiry. GEOLOGY is the science of the earth ; for, besides in vestigating, recording, and describing the composition, character, and structure of the rocks, it reasons from observed facts in true Baconian inductive method, and accounts for the origin and formation not only of these rocks, but also of the physical features of the earth's exterior which it is the especial function of geography to describe. But though geology is more extended in its method than geography, it is more restricted in its scope ; for while the latter deals with the whole globe, including its seas and atmosphere, its position in space, its movements, and the con ditions under which it exists, as well as its productions, both vegetable and animal, geology has to do only with that portion of it below the surface which can be known either directly or indirectly from actual observation.

This is necessarily limited to the total thickness of all the stratified rocks that can be seen, which only amounts to about -^ part of the radius of the globe, or, in other words, to the outermost shell, having a thickness of about ten miles. This, however, although so small a part, is obviously the most im portant part of the earth to us, and the investigation of its composition, structure, and character must be of the greatest value to mankind. It is, of course, of the utmost value in obtaining for man's use the mineral treasures of the rocks, metallic ores, coal, building and ornamental stones, and gems ; while it is of great use to the engineer, both civil and military, in the making of roads and other works, and especially in obtaining water for the supply of centres of population. In agriculture it is also useful, and even to the artist, who will by it the truer to Nature paint his pictures, for the geological structure of a district determines the character of the scenery not merely in its great features, but also as affected by its trees and other vegetation.

And again, by determining the mineral and affecting the vegetable productions of a country, it likewise determines or affects the occupations and social condition of its inhabitants, and even to some extent their political condition and characteristics. Thus, had the Coal Measures not been denuded to so large an extent in Ireland, leaving the underlying Carboniferous Lime stone to lorm so great a portion of the whole area of the island, its inhabitants would have been a manu- INTRODUCTORY. 19 facturing rather than a pastoral people, with great centres of population and wealth. The broad teachings of geology, and the deductions to be drawn from geological facts, are therefore many, varied and far-reaching, even for practical purposes. But the advantages of geological teaching do not end here.

Its educational and expanding influence on the mind is also great, since it reveals Nature's method of dealing with, and acting upon, the rocky platform on which man plays his part and the successive phases through which it has passed, as well as the character of the inhabitants of the lands and waters of the globe, and of the vegetation that clothed the earth during the epochs previous to human existence. It teaches the continuity of Nature, both animate and inanimate, and shows that that continuity has co existed, and has been coincident, with a gradual ex pansion of the area, so to speak, of vegetable and animal morphology, and with, at the same time, a progressive development of organic form, structure, and capabilities. It furthermore assists in the re production of the geography, or rather in the delinea tion of the configuration of land and sea, as well as of the great contours of the land masses of far distant periods.

Geology, again, gives an additional use for every fact relating to the earth acquired by observation or learnt by the study of any other of the physical sciences, since it draws upon all for illustration and support, and binds together isolated facts and distinct phenomena to make use of the whole as a strong pillar of Geological Truth. In thus giving and foster- 2 — ing the habit of observation, geology serves a high purpose, since the whole mental calibre and the in tellectual capacity of the individual are thereby increased and developed. In giving an acquaintance with the structure of the rocks and the prominent features of a landscape, of hill and valley, of mountain, and precipice, and plain, as well as with their origin and cause, geological know ledge adds greatly to the interest and charm of travel, whether limited to a county or extended to a con tinent, and so gives what the monarch of old sighed for in vain — a new pleasure, it might almost be called a new sense, and one not satiating or diminishing, but of lifelong duration.

Another result even of a superficial knowledge of geology, but one with which it is not usually credited, is its religious or reverential effect on the mind ; for surely no one can have his conceptions of the duration of the earth and universe infinitely increased without having also increased his reverence for the Almighty Power that worked alike in the far-off æons of the past, as during the comparatively few centuries of man's existence on the earth. Indeed, geological teaching of the vastness of the age of the universe corresponds in spirit with astronomical teaching of the vastness of its extent, both equally proclaiming corresponding truths that support each other and confirm and deepen the mental impression of the infinite greatness and grandeur of the Material Universe. Thus does the study of Nature bring about the fulfil ment of the presage of the inscription ' Deo Gloria ' on the ancient coin discovered at York.so significantly, INTRODUCTORY. 21 at the founding of the British Association for the Advancement of Science.

Yet, important as is geological investigation, the present Science of Geology is of very recent origin. It is true that Pythagoras and Aristotle, and a few Roman philosophers, had some right ideas as to the origin of the rocks and their organic contents ; yet, during the long period from their days to the last century, scarcely a ray of light, with the exception of the teaching of Leonardo da Vinci as to the origin of fossils, illumined the geological darkness of the human mind. In the latter part of the eighteenth century Werner, of Freiberg, in Saxony, propounded the hypothesis that all rocks were of aqueous origin, and so gave rise to the Neptunists, who opposed the Vulcanists, or those who held that the rocks had been formed by fire. A little later, in 1788, Hutton, in our own country, published his ' Theory of the Earth,' in which he ascribes the stratified rocks to the agency of water, and the unstratified and intrusive rocks to that of heat, and, moreover, proclaimed the now established great principle of geology : that we have only to seek amongst the forces and operations of Nature now acting for the cause of all the phenomena presented by the present structure of the globe.

William Smith followed with his great discovery that groups of strata or ' formations ' may be identified by the organic remains or fossils they contain, and produced the first geological map of England.* Hutton and Smith * Now to be seen on the walls of the Geological Society, Burlington House. may, therefore, be rightly named the fathers of modern geology. Since their time, and especially during the last fifty years,* geological observers and thinkers have been numerous, especially in Great Britain, and have greatly advanced the science by accumulating a vast amount of mineralogical, petrological, stratigraphical, and palæontological data. During this period three schools cf geological thinkers have one after another commanded assent. The earliest, the Convulsionists, considered that Nature's forces produced greater and more rapid effects in the past, frequently causing tremendous convulsions or cataclysms.

The second, the Unifor mitarians, headed by Lyell, maintained the uniform action of Nature, and required vast periods of time only to account for all phenomena with the forces of Nature acting as slowly as at present. And the third and latest school, the Evolutionists, led by Herbert Spencer and Professor Huxley, hold that new con ditions may not only accelerate or retard the action of the agencies of Nature, but actually bring into play new ones. Thus the new condition of the existence of man on the earth can affect, and has affected, the operations of Nature in a marked degree. But geologists of all these schools recognise the great principle of geological investigation before stated : that the past must be read by the light of the present ; that the phenomena presented by the rocks and physical features of the earth's exterior must be ° See Presidential Address to the Geologists' Association, November, 1887, by F. W. Rudler, F.G.S. INTRODUCTORY. 23 explained by Nature's method of working now.

A knowledge of the forces and operations of Nature now acting and affecting the exterior shell of the globe is consequently first of all to be acquired by the geological inquirer. It will then be his business to make himself acquainted with the character of the materials of which the great rock masses of the earth are made up and the general characters of the rocks themselves, and afterwards to obtain a knowledge of the structure of these rock masses and the phenomena they present on a large scale, all the while applying the knowledge he has obtained of the method of Nature's acting to the explanation of these phenomena. This knowledge will still serve him in good stead when he passes to the consideration of the physical features of the earth's surface, and will be likewise essential when subsequently the rocky strata are successively examined to reveal the history of the formation of the present surface of the globe and the progress of life on the earth.

Chapter II. Agencies Affecting The Exterior Shell Of The Globe

— INORGANIC. Atmospheric and Thermal— Aqueous— Glacial— Volcanic — Seismic — Upheaval and Subsidence. The Forces and Operations of Nature at present affecting the exterior of the globe, and now altering the configuration of land and sea, and modifying the contours and sculpturing of all land surfaces, are chiefly matters of common observation, being known almost as well to any intelligent observer of Nature as to the student of science. It is only necessary for geological purposes that these various operations should be carefully noted, and arranged in such a way that their precise and definite effects on the surface of the earth may be distinctly perceived and fully apprehended. It is therefore desirable to group them under headings as correctly as possible, for some of these operations are of such a character that it is difficult to say whether they ought to be classed with one or another group, partaking as they do of the nature of both.

The Atmospheric and Thermal Agencies pro duce great effects, though some, not being conspicuous INORGANIC AGENCIES. 25 or rapid, are often overlooked. Variations of Tempera ture, producing alternate expansion and contraction, cause splits and fissures in exposed rocks, and prepare for subsequent decomposition, disintegration, and destruction of great rock masses. Evaporation, again, causing drying or desiccation, and consequently shrinkage, produces cracks, which admit the chemically acting agents, air and water, to lower depths. Evaporation also causes the saltness of lakes having no outlet, their diminution in area, and their ultimate conversion into salt plains. Decomposition by means of the gases in the atmosphere produces slow but great effects, and reduces the hardest rocks to the softest clay.

The oxygen of the air is a powerful chemical agent of change, uniting so readily as it does with many elements. The carbonic acid contained in the atmosphere effects the destruction of exposed granitic masses by uniting with the potash of felspar, and producing thereby a soluble compound, carbonate of potash, which, dissolved and carried away by the rain, leaves the other constituent of the mineral, silicate of alumina, as a soft clay, and so brings about the dis integration and destruction of the whole agglomera tion of quartz, felspar, and mica, called granite. The sulphuric acid of the atmosphere also exerts a decom posing influence on rocks. Especially is this the case with magnesian limestones which, containing carbonate of magnesia, are readily attacked by the sulphuric acid, forming a soluble compound with the magnesia, sulphate of magnesia, which is none other than Epsom salts.