232 ZOOLOGICAL GEOGRAPHY. [part hi. 



of the Palsearctic region, it is evident tliat it owes many of its 

 deficiencies and some of its peculiarities to the influence of the 

 Glacial epoch, combined with those important changes of physi- 

 cal geography which accompanied or preceded it. The elevation of 

 the old Sarahan sea and the complete formation of the INIediterra- 

 nean, are the most important of these changes in the western 

 portion of the region. In the centre, a wade aim of the Arctic 

 Ocean extended southward from the Gulf of Obi to the Aral and 

 the Caspian, dividing northern Europe and Asia. At this time 

 our European and Siberian sub-regions were probably more 

 distinct than they are now, their complete fusion having been 

 effected since the Glacial epoch. As we know that the Himalayas 

 have greatly increased in altitude during the Tertiary period, it is 

 not impossible that during the Miocene and Pliocene epochs the 

 vast plateau of Central Asia was much less elevated and less 

 completely cut off from the influence of rain-bearing winds. It 

 might then have been far more fertile, and have supported a rich 

 and varied animal population, a few relics of which w^e see in 

 the Thibetan antelopes, yaks, and wild horses. The influence 

 of yet earlier changes of physical geography, and the relations of 

 the Palffiarctic to the tropical regions immediately south of it, 

 will be better understood when we have examined and discussed 

 the faunas of the Ethiopian and Oriental regions. 



