We have already seen how Dana supposes =two= such events, one at the close of the "Palaeozoic age," and the other at the close of the "Mesozoic," merely to account for the astonishing disappearance of species at these periods when the fossils are arranged in taxonomic order; but if we once admit such an event =with Man and all the other species contemporary with one another=, where shall we limit its power to disturb the land and water and churn them all up together, leaving the present simply as the ruins of that previous world? The fact is, the current Geology is wholly built up from the Cambrian to the Pleistocene on the =dogmatic denial= that any such catastrophe has occurred to the world in which Man lived, for =one= such event happening in our modern homogeneous world is enough to make the whole pretty scheme found in our text-books tumble like a house of cards. Like the patient and exact observations of the Ptolemaic astronomers, which accumulated volumes of evidence contradicting their own theories, and which in the hands of Copernicus and Galileo, Kepler and Newton, sealed the doom of astronomical speculation and laid the foundations of an exact science of the heavens; so have the indefatigable labors of thousands of geologists accumulated evidence which strikes at the very foundation of the current Uniformitarianism, and casts a pall of doubt over every conclusion as to how or when any given deposit of the "older" rocks was produced. Here we must leave the question for the present. The possibility of such a world-wide catastrophe, which might account for the major part of the geological changes, needs no apology here. The slightest disturbance of the nice equilibrium of our elements would suffice to send the waters of the ocean careering over the land; and in the abundance of astronomical causes competent for such disturbance we cease to regard such an event as necessarily contrary to "natural law." The possibility of such a thing no competent scientist now denies; it is the problem of =recovery= from such a disaster which makes the perplexity. But incredible or not as the latter may be regarded, I claim to have established a perfect chain of scientific argument proving a world-wide catastrophe of some sort since Man was upon it. But this fact, if once admitted, strikes at the very foundation of the current science, and bids us readjust our theories from this view-point. The venerable scheme of a life succession =becomes only the taxonomic or classification series of the world that existed before this disaster=, and it becomes the business of our science to find out how many and what deposits were =due to this event=, and what were accumulated during the =unknown period= of previous existence. Those of us who wish to speculate can then let our imaginations have free play as to the uncounted ages before that event; but the "phylogenic series" as a rational scientific theory is in limbo forever.