Fourthly. It is demonstrated that the present continents of the globe, with perhaps the exception of some of their highest mountains, have for a long period constituted the bottom of the ocean, and have been subsequently either elevated into their present position, or the waters have been drained off from their surface. This is probably the most important principle in geology; and though regarded with much scepticism by many, it is as satisfactorily proved as any principle of physical science not resting on mathematical demonstration. Fifthly. The internal parts of the earth are found to possess a very high temperature; nor can it be doubted that at least oceans of melted matter exist beneath the crust, and perhaps even all the deep-seated interior is in a state of fusion. Sixthly. The fossiliferous rocks, or such as contain animals and plants, are not less than six or seven miles in perpendicular thickness, and are composed of hundreds of alternating layers of different kinds, all of which appear to have been deposited, just as rocks are now forming, at the bottom of lakes and seas; and hence their deposition must have occupied an immense period of time. Even if we admit that this deposition went on in particular places much faster than at present, a variety of facts forbids the supposition that this was the general mode of their formation. Seventhly. The remains of animals and plants found in the earth are not mingled confusedly together, but are found arranged, for the most part, in as much order as the drawers of a well-regulated cabinet. In general, they appear to have lived and died on or near the spots where they are now found; and as countless millions of these remains are often found piled together, so as to form almost entire mountains, the periods requisite for their formation must have been immensely long, as was taught in the preceding proposition. Eighthly. Still further confirmation of the same important principle is found in the well-established fact, that there have been upon the globe, previous to the existing races, not less than five distinct periods of organized existence; that is, five great groups of animals and plants, so completely independent that no species whatever is found in more than one of them, have lived and successively passed away before the creation of the races that now occupy the surface. Other standard writers make the number of these periods of existence as many as twelve. Comparative anatomy testifies that so unlike in structure were these different groups, that they could not have coexisted in the same climate and other external circumstances.