THE RECORD.

ROCK-FORMATIONS AND LIFE-PERIODS OF GEOLOGY.

In the preceding chapter we have endeavoured to lay before the reader a brief sketch of the PRESENT LIFE OF THE GLOBE-its plants and animals; the causes which seem to affect their growth; the conditions that govern their geographical distribution; their ordinal characters, as known to the botanist and zoologist; and the functions they are apparently destined to perform in the economy of creation. We now turn to that which is extinct-to that which geology exhumes from the rocky crust, and palæontology reinvests with verdure and vitality, as it clothed the forests and peopled the fields and waters thousands of ages before the human eye was created to be gladdened by its beauties or startled by its marvels. Before we can institute a satisfactory comparison, however-before we can decide between the older and the newer, and trace the order of their incomings and their outgoings in the scheme of nature-we must first appeal to the geologist for the order, in point of time, that prevails among the stratified formations.

In the "crust" or accessible portion of the globe, we discover two great sets of rocks-the one massive and unstratified, like the solidified lavas of Hecla and Vesuvius, and evidently the products of igneous eruption; the other

stratified, or occurring in layers, like the silt of lakes and seas, and undoubtedly the results of sedimentary or aqueous operations. Between these two great forces-the aqueous and igneous—the crust of the earth is ever held in habitable equipoise and never-ending variety of superficial aspect. As the former tends to waste and wear down, and carry the eroded material to the bottoms of lakes and estuaries, there to be spread out in layers of varied consistency, so the latter as incessantly strives to elevate and reconstruct— here throwing up the sea-bed into new islands, there disrupting and undulating the solid crust, and anon casting forth from volcanic craters new rocks and rocky compounds. These forces being incessantly active, such transpositions of sea and land must have frequently taken place-piling the newer deposits over those of earlier dates, varying it every turn the relative distribution of sea and land, and offering different conditions of life to plants and animals at each successive mutation. And as the sediments of existing lakes and seas envelop the remains of plants and animals that have lived in their waters, or been borne thither by floods and rivers, so also must there have been entombed in the sediments of former epochs the plants and animals of the period-the deepest being the oldest or first-formed, and the others occurring above them in order of time or superposition. This is the great key to geological sequence: the deeper, the older, and the older, the wider the difference between fossil plants and animals and those now existing. To the paleontologist this physiological difference becomes, as it were, the measure of chronological progress; stratigraphical sequence and vital gradation are but convertible terms; and either were resolvable into TIME could we only determine the ratio of its increment and advancement.

Presuming on the uniformity of nature's operations—and

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without this presumption the history of the Past would be an uncertainty and delusion-the geologist proceeds to unfold the history of the stratified deposits, tracing back from the silt of yesterday's tide to the first-formed strata; and this through the lapse of ages for which chronology has no name save cycles" and "systems" of indefinite duration. Geology is not entitled-it dare not, in the spirit of true philosophy, appeal to "abnormal conditions," to "cataclysms," or to "revolutionary forces," for a solution of its problems. Certain agents may act over certain areas with greater intensity at one period than at another, or may exert themselves, in the varying distributions of sea and land, over wider areas; still the results are homologous though differing in magnitude, and cannot be ascribed to convulsion or disorder. Where geology cannot explain, it can at least observe and describe, and this its legitimate cultivators will ever do, rather than take shelter under the assumption of abnormal conditions in primeval nature. There is ever much more philosophy in honest doubt than in the utmost ingenuity of unsupported assumption.

"The agencies," we have elsewhere observed, "that now operate on and modify the surface of the globe; that scoop out valleys and wear down hills; that fill up lakes, and estuaries, and seas; that submerge the dry land, and elevate the sea-bottom into new islands; that rend the rocky crust, and throw up new mountain-chains; and that influence the character and distribution of plants and animals,are the same in kind-though differing, it may be, in degree as those that have operated in all time past. The layers of mud, and sand, and gravel, now deposited in our lakes and estuaries, and along the sea-bottom, and gradually solidifying into stone before our eyes, are the same in kind with the shales and sandstones and conglomerates that

* Advanced Text-Book of Geology.

compose the rocky strata of the globe; the marls of our lakes, the shell-beds of our estuaries, and the coral-reefs of existing seas, year after year increasing and hardening, belong to the same series of materials, and in process of time will be indistinguishable from the chalks, and limestones, and marbles we quarry; the peat mosses and jungle growth, and the vegetable drift that have grown and collected within the history of man, are but continuations of the same formative power that gave rise to the lignites and coals of the miner; the molten lavas of Ætna and Vesuvius, and the cinders and ashes of Hecla, are but repetitions of the same materials which now compose the basalts and greenstones and trap-tuffs of the hills around us; the corals, and shells, and fishes, the fragments of plants, and the skeletons of quadrupeds, now imbedded in the mud of our lakes and estuaries and seas, will one day or other be converted into stone, and tell as marvellous a tale as the fossils we now exhume with such interest and admiration." Without this uniformity in the great operations of nature, our reasonings would be baseless, our conclusions a dream. We can only read the Past as connected with the Present, and premise of the Future from what is now taking place around us.

Destroy this belief in the continuous operation of natural law, and appeal to "revolutions" and "cataclysms," and you present a world of disorder, a Creator without a plan, and the human reason striving in vain to elaborate a system from phenomena over which no system prevails. Establish this belief, and the geologist feels he is dealing with a prescient plan whose past ever bears certain appreciable relations to its present; and in tracing the development of that plan, he is animated by the high hope of ultimately attaining to some conception, however faint, of the divine idea of its Creator. And it is in this spirit of procedure that he has subdivided the strata of the earth's crust into "sys