IX.] CENTRAL ASIAN SUB-REGION. 351 



subsequent connection with the Continent. The difficulty con- 

 nected with this explanation is that it apparently necessitates a 

 pre-glacial or early glacial age for the mammaliferous deposits of 

 the Thames valley, which are almost certainly inter-glacial or 

 post-glacial. The whole subject of glaciation is, however, so 

 complicated and involved, that it is almost impossible to form 

 workable theories as to the exact mode of the repopulation of 

 Britain after the changes which took place during the glacial 

 epoch. 



In contrast to the British Isles, which are eminently of the 

 continental type, may be cited Iceland, lying near the border-line 

 between the Arctic and European sub-regions, which is as 

 markedly oceanic in its character. Beyond an occasional ice- 

 borne polar bear, Iceland possesses only the Arctic fox, and a 

 mouse, which has been stated to be a peculiar species ; the fox 

 having doubtless been originally introduced from the north on 

 floating ice. 



According to the scheme of Dr Heilprin, the next sub-region 

 on the list is that of Central Asia, which includes 

 the countries bounded on the west by the European, sSb-regi* 1 * 11 

 and on the north by the Arctic sub-region, and 

 extends eastwards as far as Mantchuria and China proper, being 

 bordered on the south by the Kuenlun and Nanshan mountains 1 . 

 A large portion of the western districts of this tract are open 

 steppes or deserts ; and in such tracts several peculiar types of 

 rodents, such as the Kirghiz jerboa (Alactaga) and the Yarkand 

 jerboa (Euchoretes\ are met with, while the saiga antelope (Saiga), 

 and the Mongolian gazelle ( Gazella guttu rosd) are likewise charac- 

 teristic types. Susliks (Spermophilus), marmots (Arctomys), and 

 picas are very abundant ; and the place of the European wild cat 

 is occupied by Pallas's cat (Felis manul), the tiger being also 

 sparingly found in the western districts, where the ounce is like- 

 wise met with. In part of this sub-region the red deer is replaced 

 by a variety or species known as Cervus xanthopygus, while 

 Yarkand is the home of a variety of the Kashmir stag (C. cash- 

 mirianus], and the Thian-Shan possesses the very fine and wapiti- 



1 Dr Heilprin included the Tibetan plateau in this sub-region. 



