However this may be, the establishment of man in those countries in which we have said that the fossil remains of land animals are found, that is to say, in the greatest part of Europe, Asia, and America, has necessarily been posterior, not only to the revolutions which have covered up these bones, but also to those which have laid bare the strata containing them, and which are the last that the globe has undergone. Hence it clearly appears, that no argument in favour of the antiquity of the human species in these different countries can be derived either from those bones themselves, or from the more or less considerable masses of rocks or of earthy materials by which they are covered. _Physical Proofs of the Newness of the Present Continents._ On the contrary, by a careful examination of what has taken place on the surface of the globe, since it has been laid dry for the last time, and its continents have assumed their present form, at least in the parts that are somewhat elevated, it may be clearly seen that this last revolution, and consequently the establishment of our existing societies, could not have been very ancient. This result is one of the best established, and, at the same time, one of the least attended to in rational geology; and it is so much the more valuable, that it connects natural and civil history in one uninterrupted series. When we measure the effects produced in a given time by causes still acting, and compare them with those which the same causes have produced since they have begun to act, we are enabled to determine nearly the instant at which their action commenced; which is necessarily the same as that in which our continents assumed their present form, or that of the last sudden retreat of the waters. It must, in fact, have been since this last retreat of the waters, that our present steep declivities have begun to disintegrate, and to form heaps of debris at their bases; that our present rivers have begun to flow, and to deposit their alluvial matters; that our present vegetation has begun to extend itself, and to produce soil; that our present cliffs have begun to be corroded by the sea; that our present downs have begun to be thrown up by the wind: just as it must have been since this same epoch, that colonies of men have begun, for the first or second time, to spread themselves, and to form establishments in places fitted by nature for their reception. I do not here take the action of volcanoes into account, not only because of the irregularity of their eruptions, but because we have no proofs of their not having been able to exist under the sea; and because, on that account, they cannot serve us as a measure of the time which has elapsed since its last retreat. _Additions of Land by the Action of Rivers._