CHAPTER I.
RÉSUMÉ.
Geology, as will be seen from the preceding details, is among the most comprehensive of the sciences. It invades the province of every one of them, and lays them all under contribution while following out its own peculiar researches. A dry description of rocks, in their simple mineral qualities, does not limit or exhaust its ample resources. Botany, zoology, meteorology—a part, in short, of every branch of natural history, as well as chemistry, physics, and astronomy, are severally enlisted in its service, and all give interest and importance to its discursive investigations. And thus, receiving gifts from every walk of science, geology gives back in turn, and imparts to each, illustrations new and rare, from its own wonderful storehouse.
Geology, considered in itself, may be pursued in three different ways, as it resolves into three great leading branches of investigation. Observing the arrangement and superposition of rocks, as exhibited in the crust of the earth, along with their mineral distinctions and fossil contents, we embrace all the objects included in descriptive or phenomenal geology. The exposition, again, of the general principles by which such phenomena can be produced, constitutes what has been termed geological dynamics,—by which are traced the laws of action of known causes, and their relation to such changes as those which geology considers. The last branch leads to a consideration of the causes in which the phenomena have originated and the doctrines deducible from them. This has been called physical geology, and embraces all that is theoretic in the science. These three branches, while thus definitively distinct in themselves, are yet frequently combined in the works of writers on the subject; nor is it easy, or even possible, in practice, to separate them, as few will be content to describe without attempting also to explain.
It has been no part of our vocation in these investigations to inquire into the origin of a material universe;—what was its pre-existent state, and by what process this globe at first was brought into an earthy concrete form. Astronomy has tried various solutions. But whether by the splintering of other worlds, or the evolution of matter from a Saturnian ring, or by the condensation of gaseous star-dust diffused through infinite space, no astronomical hypothesis has proved satisfactory. Geology is better employed when she assumes a beginning to her researches upon the visible crust of the globe. The mystery of creation is not within the range of her legitimate territory; and, while the investigation of laws and of the influence of secondary causes falls within the province of both, it may be safely admitted that neither astronomy nor geology are, of themselves, capable of giving us any real or precise account of the origin of the universe, or of any of its parts.
That we have begun with the primary rocks of the Grampians, as the most ancient division of systematic lithology, was more with a view to have some ‘principia’ for description than assumptions for theory, and because no geological research has penetrated deeper. The crust of the earth, as far as observation extends, is proved to consist in its lower parts of a series of crystalline rocks, some of which are stratified, and others unstratified, intercalating one with another, and maintaining the same relative position, each to each, as a system, in every region of the globe. Granite, gneiss, micha-schist, quartz-rock, and limestone, constitute these first outwork courses of creation; one uniform cause acting simultaneously over the earth, appears to have placed them all in position; and as no breathing animal or blossoming plant witnessed this morn-dawn of nature, the rocks belonging to the period are termed the primary or azoic series. The fossiliferous deposits follow in their due order of superposition, arranged into groups and systems according to the organic remains by which they are respectively characterized, and preserving, in their geographical distribution, the same uniform and persistent vertical arrangement as the former. Amorphous rocks, of all ages and extent, are distributed among the stratified portions of the crust, whether crystalline or sedimentary, whereby the latter are dislocated and upheaved, and the inequalities of the surface, and all the pleasing diversity of plain, hill, and mountain have been produced. It is the special object of descriptive or phenomenal geology to note all the facts connected with these appearances and changes, to collate and compare them one with another, and finally, to systematize them according to their natural affinities and relations.
Dynamical and theoretical geology, again, inquires into the supposed principles and causes in which all these arrangements have originated, and by which they have been modified. The agencies, processes, and changes which we now observe in the existing course of nature, furnish the grounds and analogies by which alone we can speculate respecting the past condition of things, subject always to the consideration that, in proportion to the difference of effects and changes in the two periods, so are the causes and agencies which produced them, as well in relation to time as to force. The enormous magnitude of the results witnessed during the more ancient geological epochs, demonstrates the intensity of the causes then in operation; and, admitting these causes to be the same in kind with such as prevail at present, we are yet warranted to infer their more violent activity, as likewise to assume a more rapid increment in their effects. Thus the geologist, from observation of the laws of crystallization now manifested in the aggregation of the elementary particles of bodies, reverts to the existence of similar forces, whatever they be, which produced the crystalline texture of the primary rocks, their fissile structure, and the separation of all those materials which exist among them in the form of gems, agates and metalliferous veins. Igneous causes he still finds in operation, as volcanoes, earthquakes, and chemical agencies closely connected with both; and the same forces he hesitates not to connect with the elevation of mountain-chains, the vast masses of plutonic matter everywhere diffused through the earth’s crust, and the disturbance, dislocation, and other changes produced upon all the stratified rocks through which this matter has penetrated. A mighty power in continual action, he further perceives in the waters of the ocean, of the atmosphere, of the rills and rivers that issue from the mountains’ side: and to such aqueous causes, operative in the past as in the present day, he refers the transport, lamination, and detrital structure of the materials of all the sedimentary deposits. Nor does he leave out of estimation the effect of assumed cosmical changes upon the temperature of the planet, and the laws that regulate the distribution of heat over the surface: causes such as these the geologist sees greatly to influence, at present, the conditions of organic life in every quarter of the globe; and hence, he justly calls for their assistance in explaining the history of those remarkable organic remains which characterize the several geological epochs.
When the geologist proceeds systematically to trace the series of these phenomena, to ascertain their causes, and to connect together all the indications of change that are found in the organic and inorganic kingdoms of nature, he attempts the structure of a Theory of creation, which shall embrace the whole course of the world, from the earliest to the present times; and which, it may reasonably be concluded, may be resolved into one great cycle, yet unfinished. But for this the materials of the science are by no means prepared, nor is its progress sufficiently advanced.
The history of organic remains forms an interesting branch of descriptive geology, where, it may be said, we find the medal-stamps of creation in the first forms of organic life that came from the hands of the Creator. The fact is all important, and the science is prepared to announce it, that in the lowest fossiliferous strata of the earth, vegetables appear among the first of all living things: the impressions of plants, and entire beds of carbonaceous matter, are found in the most ancient strata of the Silurian group of rocks. Nor less important is the fact, that the fossils which next arrest the attention are the remains of marine animals, myriads of shells, and vast numbers of fishes. Then, in the ascending series of strata, the foot-prints of birds are lower down than the impressions of the beasts of the earth. The sea, it is next discovered, swarmed with huge reptilian bodies, before mammalian quadrupeds and cattle had yet a place on dry land; and man, the noblest specimen of organic structure, the crowning apex of the pyramid of terrestrial being, is, according to the geological narrative, precisely in his place—no bone nor fragment of his kind, having been detected in the solid frame of the globe.
Such is the vista into the past opened up through these rocky entablatures of the globe. Compared with other branches of knowledge, in point of mere exciting topics of interest, geology occupies a distinguished position. Nay, the truth here, to those not conversant with the science, is even more incredible than fiction. As a study into the records of creation, geology has disclosed views, and elicited discoveries, of the works of the Divine Architect of the world, which the religious inquirer will as cordially embrace, as ignorance only can overlook or misapprehend.—Newton imagined, so porous is all earthy matter, that this terrene globe could be crushed into the size of two or three cubic inches of solid substance. Geology now shows that the most concrete rocks, chains of hills and even of mountains, the soft clays of Virginia, and loose floating deserts of sand, are many of them composed of the shields and skeletons of animalcules; evidences, through all past time, of the wondrous prodigality of nature, and of the superabundant goodness of its Author. Nothing, indeed, at first sight can appear more barren of every point of interesting illustration than the rocky masses of the earth. Tear off the grassy covering which conceals, while it freshens, the outer crust of the globe, and to mere disorder and confusion there seems to be superadded the more repulsive features of sterility and death. But examine a little deeper, and you will see order, symmetry, and beauty; what is now frigid and motionless, was once animated with the breath of life; these stony chambers beneath, the necropolis of a buried world. The study of the Course of Creation, therefore, when read aright—whether in its organic or inorganic lessons—cannot fail to present the most varied and sublime illustrations of the power, wisdom, and goodness of Him who reared the stupendous fabric, and made our earth one of the bright rolling planets of the universe.
There are many points, however, and questions of the deepest importance, that are far from being satisfactorily determined.—The progress of vegetable and animal life, for example, is supposed to correspond with the varying conditions and changes of the earth’s surface, when the races are summoned into existence, not at once, nor after short intervals, but successively, and after ages of unfathomable extent. The record, even as a chronicle of mere life and death, is a marvelous one, full of singular revelations, and disclosing types of organized being that have long been obliterated. But when as yet there was no rational head in this mundane scene, the assumption is, that the inferior tribes were for millions of years the sole living occupants of the planet! Can all the data be sound, rightly understood, and properly interpreted, that lead to such conclusions? The epic of this lengthened series of events is yet, it may be said, without a hero. The tragedy of wild revolution and carnage lacks romance in the very monotony of its devastation. And destitute alike of a moral, and of a fitting audience, the brilliancy of the representation loses half its attractions in losing all its humanity.