It is evident, that, even while confined within the limits prescribed by the Book of Genesis, naturalists might still have a pretty wide range: they soon found themselves, however, in too narrow bounds; and when they had succeeded in converting the six days of creation into so many indefinite periods, the lapse of ages no longer forming an obstacle to their views, their systems took a flight proportioned to the periods which they could then dispose of at pleasure. Even the great Leibnitz amused himself, like Descartes, by conceiving the earth to be an extinguished sun[19], a vitrified globe, upon which the vapours falling down again, after it had cooled, formed seas, which afterwards deposited the limestone formations. By Demaillet the whole globe was conceived to have been covered with water for many thousands of years. He supposed this water had gradually retired; that all the land animals were originally inhabitants of the sea; that man himself commenced his career as a fish; and he asserts, that it is not uncommon, even now, to meet with fishes in the ocean, which are still only half converted into men, but whose descendants will in time become perfect human beings[20]. The system of Buffon is merely an extension of that of Leibnitz, with the addition only of a comet, which, by a violent blow, struck off from the sun the liquefied mass of the earth, together with those of all the other planets at the same instant. From this supposition, he was enabled to assume positive dates, as, from the present temperature of the earth, it could be calculated how long it had taken to cool down so far; and, as all the other planets had come from the sun at the same time, it could also be calculated how many ages are still required for cooling the greater ones, and to what degree the smaller are already frozen[21]. _More recent Systems._