Hence our Geologist would reasonably conclude that, the probable expense of the search being so enormous, and the chance of success so remote, it would be much wiser not to make the attempt. [Illustration] [Illustration] CHAPTER XIV. SUBTERRANEAN HEAT--ITS EXISTENCE DEMONSTRATED BY FACTS. _Theory of stratified rocks supposes disturbances of the earth’s crust--These disturbances ascribed by geologists to the action of subterranean heat--The existence of subterranean heat, and its power to move the crust of the earth, proved by direct evidence--Supposed igneous origin of our globe--Remarkable increase of temperature as we descend into the earth’s crust--Hot springs--Artesian wells--Steam issuing from crevices in the earth--The geysers of Iceland--A glimpse at the subterranean fires--Mount Vesuvius in 1779--Vast extent of volcanic action--Existence of subterranean heat an established fact._ In developing the modern theory of Geology, we have all along assumed that the Crust of the Earth has been subject to frequent disturbances from the earliest ages of the world. Again and again, in the course of our argument, we have talked of the bed of the sea being lifted up, and converted into dry land; and, on the other hand, of the dry land being submerged beneath the waters of the sea. We have not even hesitated to suppose that these two opposite movements of upheaval and submersion often took place by turns over the same area; nay, that there is scarcely a region on the surface of the Globe which has not been several times submerged, and several times again upheaved. Yet all this has not been taken for granted without proof. Our readers have seen what a long array of sober reasoning may be drawn out to show that the Stratified Rocks have been, for the most part, deposited _under water_:--first, from the nature and arrangement of the materials which compose them; secondly, from the character of the Organic Remains they contain. And since they are now _above water_, it is plain that either they have been lifted or the ocean has subsided. Furthermore, if we find, as we often do, two strata in immediate succession, the one underneath, exhibiting the trees of an ancient forest still standing erect with their roots attached, the other above, abounding in the remains of aquatic animals; we must conclude that when the ancient forest flourished this portion of the Earth’s Crust was above the level of the sea; that afterward it was submerged, and a new deposit, in which the marine remains were embedded, was spread out above the earlier vegetation; and that, last of all it again emerged from the waters, and became once more dry land. Finally, when a vertical section of the Earth’s Crust exhibits a continued series of such strata alternating with each other, it affords a proof that this particular area must have been several times under water, and several times again dry land, in the long course of ages.