In like manner, the geologist, looking into the bowels of the earth, and finding here and there the remains of a tree or a saurian, presumes that they once lived and grew in the same localities, and were buried and petrified under the rock-grindings of after-ages. But he really has no absolute proof of any such thing. They may have been created in the fossil state and laid away in the strata on the same day the earth was made. But I think the scientist, knowing laws of Nature by which, with sufficiently long periods of time, all these geologic results might have been gradually brought about, is justified in believing that they too were the slow product of Nature and of time.
So we, finding that the world has certainly at some time been subjected to a heat at least sufficient to volatilize nearly every known substance, and that there are laws of Nature by which, through periods of time immensely long, the earth and the planets might have been rolled up from a gaseous nebula and bowled off in their mighty revolutions, have just as much right to say that it was so, as we have to say that the American forests grew, or that the Triassic beds were deposited.
Geology has proved that the earth, up to the primary rocks, was once a molten mass. The crystalline structure of the unstratified rocks compels to this conclusion; for minerals insoluble in water can only become crystallized in large masses by cooling from a state of fusion. If, then, the earth was once an incandescent globe of melted rocks—for everything above the granite beds must then have been in a state of vapor—it is not unreasonable to suppose that it may have existed prior to that time in a still more highly-heated condition—even volatilized, and diffused through space as rare and attenuated gases; for this is the condition which all matter assumes under sufficient degrees of heat. In fact, we must either suppose that the earth was created as a fiery liquid globe, for which we have no warrant, or we must follow back to the time when its vapors were scattered in space, unreflecting and impenetrable to light—when the earth was "without form and void, and darkness was upon the face of the deep."
Let us start, then, with that condition of things which it is now very generally conceded must once have existed—the diffusion of matter in a nebulous form throughout all space. Calculations easily made show that the nebula must have been of extreme tenuity—such that the few grains taken up on the point of a knife-blade must have been expanded to fill several cubic miles. A heat so powerful—for we know of no other force which could thus hold apart the atoms of matter—would doubtless be sufficient to resolve every known substance into its simplest elementary constituents, perhaps into a very few primordial elements; for chemists are far from being satisfied that they have arrived at the ultimate forms of matter in their list of