ped up in
such quantities in certain parts of Siberia that he and his men climbed
over ridges and mounds consisting entirely of the bones of Elephants,
Rhinoceroses, etc. From these facts it would seem that they roamed over
all these northern regions in troops as large and numerous as the
Buffalo herds that wander over our Western prairies now. We are
indebted to Russian naturalists, and especially to Rathke, for the most
minute investigations of these remains, in which even the texture of the
hair, the skin, and flesh has been subjected by him to microscopic
examination as accurate as if made upon any living animal.

We have as yet no clue to the source of this great and sudden change of
climate. Various suggestions have been made,--among others, that
formerly the inclination of the earth's axis was greater, or that a
submersion of the continents under water might have produced a decided
increase of cold; but none of these explanations are satisfactory, and
science has yet to find any cause which accounts for all the phenomena
connected with it. It seems, however, unquestionable that since the
opening of the Tertiary age a cosmic summer and winter have succeeded
each other, during which a Tropical heat and an Arctic cold have
alternately prevailed over a great portion of the globe. In the
so-called drift (a superficial deposit subsequent to the Tertiaries, of
the origin of which I shall speak presently) there are found far to the
south of their present abode the remains of animals whose home now is in
the Arctics or the coldest parts of the Temperate Zones. Among them are
the Musk-Ox, the Reindeer, the Walrus, the Seal, and many kinds of
Shells characteristic of the Arctic regions. The northernmost part of
Norway and Sweden is at this day the southern limit of the Reindeer in
Europe; but their fossil remains are found in large quantities in the
drift about the neighborhood of Paris, where their presence would, of
course, indicate a climate similar to the one now prevailing in Northern
Scandinavia. Side by side with the remains of the Reindeer are found
those of the European Marmot, whose present home is in the mountains,
about six thousand feet above the level of the sea. The occurrence of
these animals in the superficial deposits of the plains of Central
Europe, one of which is now confined to the high North, and the other to
mountain-heights, certainly indicates an entire change of climatic
conditions since the time