232 ZOOLOGICAL GEOGRAPHY. [PART III. 
of the Palearctic region, it is evident that 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 Mediterra- 
nean, are the most important of these changes in the western 
portion of the region. In the centre, a wide arm 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 we see in 
the Thibetan antelopes, yaks, and wild horses. The influence 
of yet earlier changes of physical geography, and the relations of 
the Palearctic 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. 
