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.