Having thus explained the _genesis_ of the solar system, we come down to the history of our own earth, since it shelled off the ring which formed our moon. Continuing to cool down and shrink, a thin but rigid crust of primary rocks, still bearing marks of the intense heat to which they have been subjected, was formed upon its surface; and then the vapors, with which the atmosphere had been charged, were condensed, and formed seas, which covered the whole, or the greater part, of the earth's rind. The continual agitation of these waters, and their high temperature, as they were still nearly at the boiling point, disintegrated and wore down many of these rocks, and, in the lapse of ages, deposited their remains, in thick layers of sand and mud, at the bottom of the seas. Baked by the heat from beneath, and pressed by the weight of superincumbent waters, these layers slowly hardened into stratified rocks. Forms of vegetable and animal life, though only of the lowest type, the origin of which is to be explained hereafter, now began to appear. Some sea-plants, zooephytes, infusory animalcules, and a few of the molluscous tribe, all low down in the order of being, but important from their immense numbers and joint action, commenced their work of absorbing the carbonic acid with which the air was overcharged, and building up vast piers and mounds of stone from their own remains. Meanwhile, the internal fires of the earth occasionally broke through the rocky crust that imprisoned them, threw up liquid primitive rock through the rents, and distorted and tilted up the strata that had been formed above.