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MAGAZINE OF POPULAR SCIENCE,
JOURNAL OF THE USEFUL ARTS.
A POPULAR COURSE OF GEOLOGY.
INTRODUCTION. Sir John HERSCHEL has said that Geology, in the magnitude and sublimity of the objects of which it treats, ranks in the scale of the sciences, next to Astronomy; to which we may add, that it will ever be more generally cultivated, because a knowledge of it is more easily attainable. It may be successfully pursued without that severe preparatory discipline of mathematical study which is required of the votaries of astronomy, before they can advance even to the threshold of her temple. In making this assertion, we by no means deny the dependence of geology on the other sciences; we admit, on the contrary, that he who would be a perfectly accomplished geologist, ought to be familiar with the whole circle of them. He ought to be thoroughly versed in mathematics and general physics, in order that he may know what are, and what are not, sound data on which to found his inferences—he ought to be skilled in mineralogy, that he may know the proximate constituents of rocks. Of the general results of chemistry he must not be ignorant, and he will find it a great advantage to be expert in chemical analysis. The organic remains entombed in the strata, will make constant demands upon him for a knowledge of zoology in all its branches, and in particular he ought to possess such an intimate acquaintance with those nice distinctions which constitute specific differences in conchology, as of itself requires the study of a whole life, and such a profound knowledge of comparative osteology, as enabled Cuvier, from the examination of detached bones, to remodel the entire skeletons of animals of unknown genera: such is the barmony of proportion, the adaptation of means to ends, and of parts to uses, which the wisdom of the Creator has manifested in the structure of organic bodies. The geologist ought moreover to be a botanist of the highest order, and in the most extensive sense of the term. He ought to be able not merely to refer a plant to its place in some artificial system, by counting its stamina,-a process which he will rarely, if ever, have an opportunity of applying to the fossil vegetation of former worlds,—he ought to be able, from the examination of a stem, a leaf, or a seed-vessel, to determine the natural group to which the plant belongs, and by pointing out its habits, to throw light on the circumstances under which the stratum containing it was deposited. He ought, moreover, to be a good draughtsman, and a skilful practical surveyor. Acquirements so varied and extensive as these are attainable by few, and yet much may be done in geology with a very limited proficiency in these branches of knowledge. Without a very profound acquaintance with any of them we may master VOL. II.
all the facts of the science, and all the inferences deducible from them, and what is more, we may be qualified to institute active original research, and to enroll our names on the list of those who have added, by their discoveries, to the sum of human knowledge,—for geology is a science of observation. It is, moreover, a young and advancing science, many of whose data remain to be collected, and in the collection of them there are few who cannot assist. When we know about a dozen the most common, simple minerals,—when we can recognise their combinations in rocks,—when we know the technical terms of the science, and can distinguish crystalline from sedimentary, stratified from unstratified rocks,– and when we know the order in which the strata composing the earth's crust succeed each other, we are qualified to examine nature for ourselves, and to study geology, where it is best studied, in the field. We require not the expensive observatory or laboratory of the astronomer or the chemist, --all we want is a good hammer, and a strong arm to use it, active legs, a quick eye, and sufficient common sense to enable us to reason upon what we see.
For the rest we may trust to the assistance of our fellowlabourers, and to that community of feeling by which they are ever animated; for geology is eminently a social science, and the great and rapid advances which it has made within the last few years, are in a great measure to be attributed to that division of labour, and that mutual co-operation which can only be effected by numbers acting in concert. “ These volumes," says Mr. Murchison, speaking of the Transactions of the Geological Society of London, “must ever be valuable as the true records of our scientific progress; but great as may have been the acquirements of their authors, few indeed are the memoirs which have been completed without the aid of other distinguished fellows of the society, who, each in the branch of natural knowledge for which he stands preeminent, comes to the assistance of his wandering associate, and enables him to clothe his memoir in an appropriate dress. For where is the working geologist who, unassisted, can unravel the delicate and obscure complications of fossil organic structure? Do his fossil shells require to be identified, has he not the assistance of a Sowerby? and if these types of a former state of nature call for a comparison with existing species, is not a Broderip ever prompt in affording him the result of experienced discernment, and in unfolding the riches of his unrivalled cabinets? If he meet with difficulties in the determination of Mammalia, are not a Mantell and a Clifft at hand, to explain their relations and define their characters? Or if bewildered in the obscurity of fossil vegetation, is he not assisted by a Lindley? Have not, in fine, a Turner, a Prout, a Faraday, and a Herschel been willing instruments in enabling him to explain those laws of chemical change, without which the recondite parts of the science might have remained in utter darkness? Surely every contributor to our Transactions will acknowledge with gratitude the aid he may have received from several of our most gifted members, who, unambitious of personal fame, have been contented with the delightful consciousness of being sure, though silent, instruments in urging on the advance of truth. It is this kindly principle of co-operation, this true latent heat of the Geological Society, so ready to manifest itself on every occasion fitted to call it forth, which, warming and vivifying our endea
vours, gives to our proceedings their consistency and their strength, and enabling us to grapple with our hundred-headed science, constitutes the mainspring of our prosperity*.”
If geology yields to astronony in the sublimity of the objects of which it treats, and in being unable to bring its truths within the pale of mathematical demonstration, it possesses this advantage, as a science for popular study,--that it presents them to us in a more palpable shape. One of the first, and hardest lessons which we have to learn of the astronomer, is to discard impressions founded on what we deem the evidence of our senses.
Misled by these, we have been accustomed to consider the earth as at rest, and the sun as making a daily circuit round it. The astronomer demonstrates the contrary, and corrects our notions as to the relative size of the celestial bodies. He determines the figure of the earth, and the form of the orbit in which it moves, and ascertains the velocity of its daily and annual motion. He determines the magnitude of the sun, and its distance from us, and shows us other planets revolving round it, with their attendant satellites, and obeying the same laws which regulate the motions of that which we inhabit. He pushes his discoveries to the utmost verge of the visible creation; and, by the aid of powerful optical instruments, resolves those twinkling points, which we call the fixed stars, into groups of suns moving round each other in “mystic dance;" and he demonstrates that those laws of gravitation, which regulate the fall of bodies on the earth, are universal laws, which are obeyed in the remotest system of worlds within the reach of mortal ken. He can calculate, not only the motions of the bodies composing the planetary system, and point out their relative positions for any period of past or future time, but he can predict, within a few hours, the return of those mysterious wanderers, whose course extends into the regions of space, far beyond the remotest planet of our system, and whose periodic times are measured, not by days, but by years. It may be well said that in all this there is an overwhelming sublimity. The distances treated of are so immense, and the time required to complete some of the celestial cycles so vast, that they elude the grasp of our comprehension ;—we may talk about billions and trillions of miles, and myriads of years, but we have scarcely a less vague conception of them, than we have of infinity of space, and eternity of time. Geology, on the contrary, appeals directly to our senses. She lays open the ground on which we tread, and convinces us, that the vast secular periods of the astronomer, which, with him, are mere abstract arithmetical truths, which he cannot prove to have had an actual existence, may all have been required for the production of those changes on the surface of our globe of which we witness the monuments. She proves that our present continents, with the most elevated of their mountains, were formed at the bottom of the ocean; and that our hardest rocks were once sand, and gravel, and mud derived from the wearing down of land no longer in existence. She points to a bed of rock, a few feet in thickness, teeming with the remains of organic life; and, from the successive generations of individuals which it contains, and from other indications, into which we will not at present enter, proves that a very long period must have been
• Murchison's Anniversary Address—Proceedings of the Geological Society.
required for its formation. She then conducts us through a vast series of similar sub-marine deposits five or six miles in depth (how exposed to our view will be explained hereafter) abounding with the remains of plants and animals, and containing, not only the relics of successive generations of individuals, but of successively created races, each group of strata having its peculiar group of organic remains. She unfolds, , page after
page of this great book, this wondrous record of the changes our earth has undergone, and of the tribes of beings by which it has been peopled during a series of periods, of long but unknown duration, before it was inhabited by man. She first leads us to those formations now in progress in which he and his works are imbedded, together with the remains of this contemporary species of plants and animals. This page of the world's history is soon read.
Man is found to be but a creature of yesterday, compared with the globe he inhabits, and with the other beings with which it has been peopled. The very species of plants and animals now existing are found to have been called into being before him, for their remains occur in older, that is in deeper strata. The remains of existing species are found to be gradually intermixed with those of species that have vanished from the face of the earth. The proportion of extinct species increases as we descend. We come to lower beds still, in which not only extinct species occur, but extinct genera. The forms of organic life recede more and more from existing types, and they diminish in number in the lower rocks, till, at last, we lose all traces of them entirely. During our progress through this vast series of rocks, evidently of submarine formation, we meet with others bursting through them, which are as clearly of igneous origin, and derived from below. The lowest rocks we meet with are of this igneous character, and contain no organic remains. It
be that we have reached the records of a period when the world was unfit for the support of animal and vegetable life. It may be that the earlier
pages of its history have been torn out, and that the rocks in question once contained the remains of still older races, but that all traces of them have been obliterated, by the fusion to which the rocks have been exposed. At all events, we have reached the dark
of the earth's history, and we close the book. With speculations on the creation of the world,—on the mode in which it was reduced from a chaotic state,
and of the causes which gave it its present figure, we have nothing to do. They were favourite themes with the geologists of former days, whose wild reveries threw a discredit on the science, from which it was long in recovering, even after its votaries began to walk in a more sober path. The cosmogonists, as they are called, applied themselves to the invention of modes in which worlds might be created, with an industry, which, if applied to the observation of phænomena in the world around them, might have led to important knowledge. But that was too humble a task for them. They preferred the field of imagination, and all their labours in that field tended but to bring chaos back again. In contemplating their worlds, it would seem as if “ nature's journeymen had made them,” and had not made them well.” And yet they arrogated to themselves a command over all the powers of nature, and they were not sparing in their use of them. They made the globe solid or hollow,