Page:Popular Science Monthly Volume 44.djvu/637

 and other reasons, no longer inhabitants of the countries where fossil man has been found; hence, as related to those countries, they are all extinct.

It will be noticed that, of these animals as we now know them, the lion, tiger, hyena, and hippopotamus are tropical, or indigenous to warm climates. The reindeer and musk ox are arctic, and no doubt the extinct mammoth and woolly rhinoceros were arctic also. During glacial times these arctic and tropical animals appear to have occupied the same territory contemporaneously. This fact seems more particularly conspicuous with the lion, tiger, hyena, hippopotamus, mammoth, and woolly rhinoceros; the reindeer and musk ox appearing, at least abundantly, somewhat later. This fact has given rise to considerable difference of opinion. It has been argued that the tropical forms are

post-glacial, and that subsequent to the Glacial period the glaciated area passed through a period of tropical conditions.

This argument seems clearly untenable from any point of view, as there is no evidence of a tropical climate intervening between the Glacial epoch and the present temperate climate. All the evidence shows a gradual amelioration of climate until the present conditions are reached. Again, as the mammoth and woolly rhinoceros, supposed to be arctic forms, appear associated with the tropical forms in the same deposit, side by side, they would have to be considered tropical. For this there is reason, as their present representatives, the elephant and rhinoceros, are tropical.

But the facts are these: the reindeer and musk ox, known arctic forms, appear later than the supposed tropical forms. In all excavations through glacial material the tropical forms with mammoth and woolly rhinoceros appear in the lower levels, never superficially; where several fossil beds are gone through, the upper or superficial beds contain the reindeer more