CHAP. VIII.] PHYSICAL FEATURES. 265 



remarkable admixture of mammalian genera now respectively 

 confined to the Ethiopian and Oriental regions, together with 

 some of a Holarctic facies ; and the completion of the elevation 

 of the Himalayan chain was probably an important factor in the 

 dispersal and differentiation of this common fauna. Holarctic 

 types are again met with in force in the open desert regions on 

 the north-western frontier of India. On the other hand, the 

 fauna of the Philippines exhibits an approximation to that of the 

 Austro-Malayan region, and thus shows a blending between the 

 Arctogaeic and Notogaeic realms. In physical features the Oriental 

 region displays great variation, a large portion of peninsular India 

 consisting of open dry grassy plains, whereas the slopes of the 

 eastern Himalaya, together with the greater part of Assam, Burma, 

 and the Malayan countries are clad with luxuriant forests ; these 

 tropical or sub-tropical forest-regions being those where the fauna 

 attains its fullest and richest development. 



The poorest part of the region is, as Dr Wallace 1 observes, the 

 great triangular plateau forming the Indian peninsula; this area 

 differing remarkably from the Himalaya in its geological features, 

 and having been land since an extremely ancient date, whereas 

 the Himalayan area consists very largely of marine formations. 

 Since it is stated in the passage cited that peninsular India 

 during the Tertiary period existed as an island entirely discon- 

 nected from the Himalaya and Burma, it may be well to quote 

 the later and more authentic views of the authors of the Manual 

 of the Geology of India 2 on this subject. After reference to the 

 extent of Eocene rocks in northern India, it is there stated that 

 " the Peninsula of India in Eocene times was part of a tract 

 of land, perhaps of a great continent united to Africa ; that there 

 was a sea to the eastward, extending far to the north-east, in the 

 region now occupied by the Assam hills, and another sea to the 

 north-west, covering great part, if not the whole, of Persia, Baluch- 

 istan, the Indus plain, and a portion of the upper Ganges plain. 

 An arm of this sea extended from the north-west up the Indus 

 valley in Ladak. The Himalaya, and perhaps Tibet, wholly or 

 in part, were raised above the sea ; but formed in all probability 



1 Geographical Distribution of Animals, vol. I. p. 314. 



2 First edition, pt. I. p. liii. 



