Whoever goes into a careful examination of the rocks will soon become satisfied that no fragment of them all remains in the condition in which it was originally created. Whatever was the original form in which matter was produced, there is no longer any example of it to be found. The evidence of these changes is as strong almost as that constant changes are going on in human society. And we find them constantly progressing among the rocks, as well as among men; nor do the agents by which they are produced appear to have been ever different from those now in operation. The two most important are heat and water; and it is doubtful whether there is a single particle of the globe which has not experienced the metamorphic action of the one or the other. Indeed, it is nearly certain that every portion of the globe has been melted, if not volatilized. All the unstratified rocks have certainly been fused, and probably all the stratified rocks originated from the unstratified, and have been modified by water and heat. In many of these rocks, especially the oldest, we perceive evidence of the joint action of both these agents. Evidently they were once aqueous deposits; but they appear to have been subsequently subjected to powerful heat. As we ascend on the scale of the stratified rocks, the marks of fire diminish, and those of water multiply, so that the latest are mere mechanical or chemical depositions from water. In these facts, then, we see proof that heat and water have been the chief agents of geological change since the first formation of a solid crust on the globe; for some of the rocks now accessible, as already stated, date their origin at that early period. We might also trace back the agency of heat much farther, if the hypothesis adopted by not a few eminent geologists be true, which supposes the earth to have been once in a gaseous state from intense heat. But to press this point will add very little to my argument, even could I sustain it by plausible reasoning. I will only say, that, so far as we know any thing of the state of the earth previous to the consolidation of its crust, heat appears to have been the chief agent concerned in its geological changes.