THE ALLIES OF THE SQUIRREL: MAMMALIA 433 



with a layer of ice, which in certain regions grew to be a 

 mile thick over the land, destroying all life or forcing it to 

 migrate southward to escape the rigors of the climate. As 

 there were several invasions and retreats of the ice, there 

 may be said to have been several glacial epochs, separated 

 by long periods of warmer weather, when the animal and 

 plant life could slowly work its way back on the edge of 

 the retreating glaciers. There is a peculiar interest to this 

 period, inasmuch as it introduces the last of the great geo- 

 logical eras, the Quaternary Period, or the Age of Man. 



A conspicuous feature of the mammalian life of the Age 

 of Man was the great size of many of the species. After the 

 opening glacial epoch the climate became mild again, and 

 this seems to have favored the development of abundant 

 vegetation and great mammalian forms. One of the largest 

 and most widely distributed species was the Mammoth 

 (EVephas primige'nius, Fig. 228), a proboscidean larger than 

 the elephant of to-day and covered with a thick coat of 

 hair, an adaptation to cold temperate regions. Its remains 

 have been found frozen in the ice of Siberia, the hair and 

 flesh perfectly preserved. Early man knew of this great 

 mammal, for a drawing of the creature is in existence, 

 made on a piece of its own tusk (Fig. 229). The mastodons 

 were somewhat similar to the mammoths, but fitted on the 

 whole for a warmer climate. There are over thirty species 

 of mastodons known, of nearly world-wide distribution. 

 They have become extinct within so short a time, geologi- 

 cally speaking, that traditions of their existence as living 

 animals occur among men. 



The remains of giant edentates have been found in South 

 America. Recent discoveries seem to show that some of them 

 were living within the period of man on that continent, for 

 some of the tribes of South American Indians have traditions 

 respecting these monsters. In Europe and Asia there were 



