II.—History of the Earth's Crust
When we study the earth's crust we find that it consists of layers or strata, laid down in succession, the earlier under the influence of heat, the later under the influence of water. These strata in their order might be described as a record of the state of life upon our planet from an early to a comparatively recent period. It is truly such a record, but not one perfectly complete.
Nevertheless, we find a noteworthy and significant sequence. We learn that there was dry land long before the occurrence of the first fossils of land plants and animals. In different geographical formations we find various species, though sometimes the same species is found in different formations, having survived the great earth changes which the record of the rocks indicates. There is an unbroken succession of animal life from the beginning to the present epoch. Low down, where the records of life begin, we find an era of backboneless animals only, and the animal forms there found, though various, are all humble in their respective lines of gradation.
The early fishes were low, both with respect to their class as fishes, and the order to which they belong—that of the cartilaginous or gristly fishes. In all the orders of ancient animals there is an ascending gradation of character from first to last. Further, there is a succession from low to high types in fossil plants, from the earliest strata in which they are found to the highest. Several of the most important living species have left no record of themselves in any formation beyond what are, comparatively speaking, modern. Such are the sheep and the goat, and such, above all, is our own species. Compared with many humbler animals, man is a being, as it were, of yesterday.
Thus concludes the wondrous section of the earth's history which is told by geology. It takes up our globe at an early stage in the formation of its crust—conducts it through what we have every reason to believe were vast spaces of time, in the course of which many superficial changes took place, and vegetable and animal life was gradually evolved—and drops it just at the point when man was apparently about to enter on the scene. The compilation of such a history, from materials of so extraordinary a character, and the powerful nature of the evidence which these materials afford, are calculated to excite our admiration, and the result must be allowed to exalt the dignity of science as a product of man's industry and his reason.
It is now to be remarked that there is nothing in the whole series of operations displayed in inorganic geology which may not be accounted for by the agency of the ordinary forces of Nature. Those movements of subterranean force which thrust up mountain ranges and upheaved continents stand in inextricable connection, on the one hand, with the volcanoes which are yet belching forth lavas and shaking large tracts of ground, as, on the other, with the primitive incandescent state of the earth. Those forces which disintegrated the early rocks, of which detritus formed new beds at the bottom of the sea, are still seen at work to the same effect.
To bring these truths the more nearly before us, it is possible to make a substance resembling basalt in a furnace; limestone and sandstone have both been formed from suitable materials in appropriate receptacles; the phenomena of cleavage have, with the aid of electricity, been simulated on a small scale, and by the same agent crystals are formed. In short, the remark which was made regarding the indifference of the cosmical laws to the scale on which they operated is to be repeated regarding the geological.
A common furnace will sometimes exemplify the operation of forces which have produced the Giant's Causeway; and in a sloping ploughed field after rain we may often observe, at the lower end of a furrow, a handful of washed and neatly deposited mud or sand, capable of serving as an illustration of the way in which Nature has produced the deltas of the Nile and Ganges. In the ripple-marks on sandy beaches of the present day we see Nature's exact repetition of the operations by which she impressed similar features on the sandstones of the carboniferous era. Even such marks as wind-slanted rain would in our day produce on tide-deserted sands have been read upon tablets of the ancient strata.
It is the same Nature—that is to say, God through or in the manner of Nature—working everywhere and in all time, causing the wind to blow, and the rain to fall, and the tide to ebb and flow, inconceivable ages before the birth of our race, as now. So also we learn from the conifers of those old ages that there were winter and summer upon earth, before any of us lived to liken the one to all that is genial in our own nature, or to say that the other breathed no airs so unkind as man's ingratitude. Let no one suppose there is any necessary disrespect for the Creator in thus tracing His laws in their minute and familiar operations. There is really no true great and small, grand and familiar, in Nature. Such only appear when we thrust ourselves in as a point from which to start in judging. Let us pass, if possible, beyond immediate impressions, and see all in relation to Cause, and we shall chastenedly admit that the whole is alike worshipful.
The Creator, then, is seen to have formed our earth, and effected upon it a long and complicated series of changes, in the same manner in which we find that he conducts the affairs of Nature before our living eyes; that is, in the manner of natural law. This is no rash or unauthorised affirmation. It is what we deduce from the calculation of a Newton and a Laplace on the one hand, and from the industrious observation of facts by a Murchison and a Lyell on the other. It is a point of stupendous importance in human knowledge; here at once is the whole region of the inorganic taken out of the dominion of marvel, and placed under an idea of Divine regulation.