The first important conclusion, to which every careful observer will come, is, that the rocks of all sorts, which compose the present crust of the globe, so far as it has been explored, at least to the depth of several miles, appear to have been the result of second causes; that is, they are now in a different state from that in which they were originally created.

It is indeed a favorite idea with some, that all the rocks and their contents were created just as we now meet them, in a moment of time; that the supposed remains of animals and plants, which many of them contain, and which occur in all states, from an animal or plant little changed, to a complete conversion into stone, were never real animals and plants, but only resemblances; and that the marks of fusion and of the wearing of water, exhibited by the rocks, are not to be taken as evidences that they have undergone such processes, but only that it has pleased God to give them that appearance and that in fact it was as easy for God to create them just as they now are as in any other form.

It is a presumption against such a supposition, that no men, who have carefully examined rocks and organic remains, are its advocates. Not that they doubt the power of God to produce such effects, but they deny the probability that He has exerted it in this manner; for throughout nature, wherever they have an opportunity to witness her operations, they find that when substances appear to have undergone changes, by means of secondary agencies, they have in fact undergone them; and, therefore, the whole analogy of nature goes to prove that the rocks have experienced great changes since their deposition. If rocks are an exception to the rest of nature,—that is, if they are the effect of miraculous agency,—there is no proof of it; and to admit it without proof is to destroy all grounds of analogical reasoning in natural operations; in other words, it is to remove the entire basis of reasoning in physical science. Every reasonable man, therefore, who has examined rocks, will admit that they have undergone important changes since their original formation.

In the second place, the same general laws appear to have always prevailed on the globe, and to have controlled the changes which have taken place upon and within it. We come to no spot, in the history of the rocks, in which a system different from that which now prevails appears to have existed. Great peculiarities in the structure of animals and plants do indeed occur, as well as changes on a scale of magnitude unknown at present; but this was only a wise adaptation to peculiar circumstances, and not an infringement of the general laws.

In the third place, the geological changes which the earth has undergone, and is now undergoing, appear to have been the result of the same agencies, viz., heat and water.

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 coëxisted in the same climate and other external circumstances.