QUATERNARY AGE 



PLEISTOCENE PERIOD 



The temperature of the northern hemisphere had been 

 more or less decHning ever since the later Miocene. This, 

 no doubt, had in great part been owing to long-sustained 

 land-upheavals. At the close of the PUocene and the com- 

 mencement of the Pleistocene the cold was steadily increasing. 



Apes and tapirs, it would seem, had migrated from Europe Europe 

 by this time ; and climate had doubtless caused many other 

 migrations, and also some extinctions. The temperature, 

 however, had not sunk so low as to prevent hippopotamuses 

 making excursions to the continent, at least in the summer 

 months. Huge elephants of the same species as those of the 

 last Period were also still able to find suitable accommodation 

 (E. meridionalis) ; and the presence of some straight-tusked 

 forms testified to fresh arrivals of proboscidean Ufe (E. 

 antiquus). Horses of a new species were now on the plains 

 (E. cahallus), as well as descendants of the zebra-Uke forms 

 of the PUocene {E. stenonis). The new-comers had migrated 

 probably from some inhospitable scenes in the north of Asia ; 

 for they bore close resemblance to the wild horses now living 

 on the deserts of that continent (E. Przewalskii). Other 

 forms appear to have been intermediate between the last- 

 named and the zebra-like animals (E. Heidelbergensis). 



Climate, however, in the more northern latitudes was 

 fast driving life down from old abodes. Many of the trees 

 and other growths in those regions must have been suffering 

 from the cold, for even the hardy Spruce Fir (Abies excelsa) 

 was beginning to retreat from its far northern ground. And 

 wolves, gluttons or wolverines (Gulo), elk (Alces latifrons), 

 musk-oxen (0. moschatus), mountain sheep (0. Savigni), and 



