Quatrefages meets this by saying that Tertiary men with a larger brain, and therefore more intelligence than the other Tertiary mammals, might have survived, where these succumbed to changes and became extinct. This is doubtless true to some extent, but it hardly seems sufficient to account for the presence of a higher and more recent type, like that of Castelnedolo in the Lower Pliocene, that is a whole geological period earlier than that of the Lower Quaternary. It is more to the purpose to say with Gaudry that the changes on which the distinction of species are founded are often so slight that they might just as well be attributed to variations of races; and to appeal to instances like that of the Hylobates of the Miocene, one of the nearest congeners of man, in which no genuine difference can be detected from the Hylobates or Gibbon of the present day; and if the discovery referred to at p. 264, of anthropoid primates in the Eocene of Patagonia, should be confirmed, it would greatly strengthen the argument for the persistence of the order to which man belongs through several geological periods. In any case we require more than the evidence of this one discovery before we can assume the type of Tertiary man as a proved fact with the same confidence as we can the existence of something like man in those remote ages, from the repeated evidence of chipped stones and cut bones, showing unmistakable signs of being the work of human intelligence. And in the meantime, the only safe conclusion seems to be that it is very probable that we may have to go back to the Eocene to find the "missing link," or the ancestral animal which may have been the common progenitor of man and of the other quadrumana. I turn now to the evidence from the New World. I have kept this distinct, for there is no such proof of synchronism between the later geological phases of this and of the Old World as would warrant us in assuming that what is true in one is necessarily true in the other. Thus in Europe the presence of the mastodon is a conclusive proof that the formation in which its remains are found is Upper Miocene or Pliocene, and it has completely disappeared before the glacial period and the Quaternary era. But in North America it has survived both these periods, and it is even a question whether it is not found in recent peat-mosses with arrow-heads of the historical Indians.