I agree, therefore, with MM. Deluc and Dolomieu, in thinking, that if any thing in geology be established, it is, that the surface of our globe has undergone a great and sudden revolution, the date of which cannot be referred to a much earlier period than five or six thousand years ago; that this revolution overwhelmed and caused to disappear the countries which were previously inhabited by man, and the species of animals now best known; that, on the other hand, it laid dry the bottom of the last sea, and formed of it the countries which are at the present day inhabited; that it is since the occurrence of this revolution that the small number of individuals dispersed by it have spread and propagated over the newly exposed lands, and, consequently, that it is since this epoch only, that human societies have assumed a progressive march, that they have formed establishments, raised monuments, collected natural facts, and invented scientific systems. But the countries which are at present inhabited, and which the last revolution laid dry, had already been previously inhabited, if not by men, at least by land animals, and, therefore, one preceding revolution at least had put them under water; and if we may judge by the different orders of animals the remains of which are observed in them, they had perhaps been subjected to two or three irruptions of the sea. _Further Researches to be made in Geology._ These alternations now appear to me to form the problem in geology that it is of most importance to solve, or rather to define and circumscribe within due limits; for, in order to resolve it satisfactorily, it would be necessary to discover the cause of these events,--an undertaking which presents a difficulty of quite a different kind. I repeat it, we see pretty clearly what is going on at the surface of the continents in their present state; we have formed a tolerable conception of the uniform progress and regular succession of the primitive formations, but the study of the secondary formations has been little more than merely commenced. That wonderful series of unknown zoophytes and marine mollusca, succeeded by reptiles and fresh-water fishes equally unknown; and these again replaced, in their turn, by other zoophytes and mollusca, more nearly related to those of the present day; those land animals, and those equally unknown fresh water mollusca and other animals which next occupied the surface, to be again displaced but by mollusca and other animals similar to those of our present seas; the relations of these diversified beings to the plants the remains of which accompany theirs, the connection of these two kingdoms with the mineral strata in which they are deposited; the greater or less uniformity existing between these different orders of beings in the different basins;--these are phenomena which appear to me imperiously to demand the attention of philosophers.