CHAP. XII.] THE ORIENTAL REGION. .363 



causes of this change were of two kinds. There was a great 

 geographical and physical revolution effected by the elevation 

 of the Himalayas and the Thibetan plateau, and, probably at 

 the same time, the northward extension of the great Siberian 

 plains. This alone would produce an enormous change of 

 climate in all the extra-tropical part of Asia, and inevitably 

 lead to a segregation of the old fauna into tropical and tem- 

 perate, ?-nd a modification of the latter so as to enable it to 

 support a climate far more severe than it had previously known. 

 But it is almost certain that, concurrently with this, there was 

 a change going on of a cosmical nature, leading to an alteration 

 of the climate of the northern hemisphere from eqiuible to 

 extreme, and culminating in that period of excessive cold whicdi 

 drove the last remnants of the old sub-tropical fauna beyond 

 the limits of the Paltearctic region. From that time, the Oriental 

 and the Ethiopian regions alone contained the descendants of many 

 of the most remarkable types which had previously flourished 

 over all Europe and Asia ; but the early history of these two 

 regions, and the peculiar equatorial types developed in each, 

 sufficiently separate them, as we have already shown. The 

 Malayan sub-region is that in w^hich characteristic Oriental 

 types are now best developed, and where the fundamental con- 

 trast of the Oriental, as compared with the Ethiopian and 

 Pahearctic regions, is most distinctly visible. 



