To apprehend fully the magnitude of the effects which may fairly be ascribed to this last-mentioned power, we must remember that, according to Geological theory, almost every portion of the Earth’s Crust has been more than once lifted up above the surface of the ocean, and afterward depressed below it. It is believed that this alternate rising and sinking was effected very often, perhaps most commonly, not by sudden convulsions, but rather by slow or gradual movements. Now, during this process, as the land was emerging from the waters or sinking beneath them, new surfaces would be presented in each succeeding century to the force of the ocean currents and the erosive action of the breakers; and it is not difficult to conceive that the accumulated ruins produced, in a long lapse of time, by destructive agents so powerful, so untiring, so universal, may have readily furnished the materials for a very large proportion of the Aqueous Rocks now in existence.
Hitherto we have considered the Crust of the Earth as a great structure slowly reared up by the hand of Nature; we have spoken of the Rocks that compose it, of their origin and history, of the order in which they are disposed, and of the various agencies that have been at work to mould them into their present form and feature. We have now to contemplate this marvellous structure under a new aspect; for we are told by Geologists that it is a vast sepulchre, within which lie entombed the remains of life that has long since passed away. Each series of strata is but a new range of tombs; and each tomb has a story of its own. Here a gigantic monster is disclosed to view, compared to which the largest beast that now roams through the forest is puny in form and contemptible in strength: there, within a narrow space, millions of minute animal frames are found closely compacted together, each so small that its existence can be detected only by the aid of a powerful microscope. In one place whole skeletons are found almost entire, embedded in the bosom of the solid rock; in another, we have a boundless profusion of bones and shells; and again in another, neither the skeleton itself appears, nor yet its scattered bones, but simply the imprint of footsteps once left upon the sandy beach, and still remaining engraved on the stone into which the fine sand has been converted chiefly by the agency of pressure. There is no scarcity of relics in this wonderful charnel-house of Nature. For half a century the work of plunder has been going on without relaxation or remorse; the tombs have been yielding up their dead; every city in the civilized world has filled its museums, and the cabinets of private collectors are overflowing: but the spoils that have hitherto been carried away seem to bear a very small proportion to those which yet remain behind.
These remains of animals and plants embedded in the Crust of the Earth are called Fossils; and Geologists maintain that the Fossils preserved in each group of strata represent the animals and plants that flourished on the surface of the Earth, or in the waters of the ocean, when that group of strata was in process of formation. There they lived, and there they died, and there they were buried, in the sand, or the shingle, or the mud that came down from the waters above. Their descendants, however, still lived on, and new forms of life were called into being by the voice of the Omnipotent Creator, making, as it were, a connecting link between the new age of the world that was coming in and the old one that was passing away. But they, too, died and found a tomb beneath the waters; for Nature, with unexhausted energies, was still busy collecting materials from the old rocks, and building up the new. And so that age passed away like the former, and another came; and every age was represented by its own group of strata; and each group of strata was, in its turn, covered over with a new deposit; and the tombs were all sealed up, with their countless legions of dead, their massive monuments of stone, their strange hieroglyphic inscriptions. At length came the last stage of the world’s history, and man appeared upon the scene; and it is his privilege to descend into this wonderful sepulchre, and to wander about amidst the monuments, and to strive to read the inscriptions. In our own days more especially, eager and enthusiastic students are abroad over the whole face of the globe, and are gathering together from every country the Fossil Remains of extinct worlds. By the aid of Natural History they seek to assign to each its own proper place in the ranks of creation; to trace the rise, the progress, and the extinction of every species in its turn; and even to describe the nature and the character of all the various forms of life that have dwelt upon the Earth from the beginning.
Such is the theory of Geology as expounded at the present day by its most able and popular advocates. We have passed over a multitude of minor details that we might not weary our readers, and we have kept aloof from disputed points that we might not get entangled in a purely scientific controversy. Our object has simply been to gather together into a systematic form those more general conclusions which, however startling they may seem to practical men of the world, and even to many of those whose minds have been accustomed to the pursuit of science in other departments, are nevertheless regarded as certain by all who have devoted their lives to the study of Geology. It now remains to investigate the facts on which these conclusions are based, and to consider the line of argument by which so many able and earnest men have been led to accept them. In this vast field of inquiry we shall chiefly direct our attention to those points that bear upon the Antiquity of the Earth; and in attempting to bring home to our readers the nature and the force of Geological reasoning, we shall confine ourselves altogether to simple and familiar illustrations.
CHAPTER II.
THEORY OF DENUDATION ILLUSTRATED BY FACTS.
Principle of reasoning common to all the physical sciences—This principle applicable to Geology—Carbonic acid an agent of denudation—Vast quantity of lime dissolved by the waters of the Rhine and borne away to the German ocean—Disintegration of rocks by frost—Professor Tyndall on the Matterhorn—Running water—Its erosive power—An active and unceasing agent of denudation—Mineral sediment carried out to sea by the Ganges and other great rivers—Solid rocks undermined and worn away—Falls of the Clyde at Lanark—Excavating power of rivers in Auvergne and Sicily—Falls of Niagara—Transporting power of running water—Floods in Scotland—Inundation in the valley of Bagnes in Switzerland.
In the physical sciences it is a common principle of reasoning to account for the phenomena that come before us in nature, by the operation of natural causes which we know to exist. Nay, this principle seems to be almost an instinct of our nature, which guides even the least philosophical amidst us, in the common affairs of life. When we stand amongst the ruins of an ancient castle, we feel quite certain that we have before us, not alone the monument of Time’s destroying power, but also the monument of human skill and labor in days gone by. We entertain no doubt that ages ago the sound of the mason’s hammer was heard upon these walls, now crowned with ivy; that these moss-grown stones were once hewn fresh in the quarry, and piled up one upon another by human hands; and that the building itself was designed by human skill, and intended for the purposes of human habitation and defence. Or, if we see a footprint in the sand, we conclude that a living foot has been there; and from the character of the traces it has left, we judge what was the species of animal to which it belonged, whether man, or bird, or beast. It is true that God is Omnipotent. He might, if it had so pleased Him, have built the old castle at the creation of the world, and allowed it to crumble slowly into ruins: or he might have built it yesterday, and made a ruin begin to be where no castle had stood before; and covered the stones with moss, and mantled the walls in ivy. And as to the footprint in the sand, it were as easy for Him to make the impress there, as to make the foot that left the impress. All this is true: but yet if any one were to argue in this style against us, he would fail to shake our convictions; we should still unhesitatingly believe that human hands once built the castle, and that a living foot once trod the shore.