302 THE ORIENTAL REGION. [CHAP. 



the first three belong to the group of stegodont, or intermediate 

 elephants. 



In endeavouring to explain the relationship of the Javan fauna 

 to that of the rest of the Malayan sub-region, Dr Wallace 1 was 

 first of opinion that Java, which was evidently isolated before 

 Sumatra and Borneo, had a brief land-connection with the Siamese 

 peninsula, independently of those two islands. This view, how- 

 ever, was subsequently abandoned 2 , and the following hypothesis 

 proposed. From the evidence of certain Tertiary rocks in Java 

 believed to be of Miocene age, it is considered probable that at 

 the epoch in question that island "would have been at least three 

 thousand feet lower than it is now, and such a depression would 

 probably extend to considerable parts of Sumatra and Borneo, so 

 as to reduce them all to a few small islands. At some later 

 period a gradual elevation occurred, which ultimately united the 

 whole of the islands with the continent. This may have continued 

 till the glacial period of the northern hemisphere, during the 

 severest part of which a few Himalayan species of birds and 

 mammals may have been driven southward, and ranged over suit- 

 able portions of the whole area. Java was then separated by 

 subsidence, and these species became imprisoned there ; while 

 those in the remaining part of the Malayan area again migrated 

 northward when the cold had passed away from their former 

 home, the equatorial forests of Borneo, Sumatra, and the Malay 

 Peninsula being more especially adapted to the typical Malayan 

 fauna which is there developed in rich profusion. A little later 

 the subsidence may have extended further north, isolating Borneo 

 and Sumatra, but probably leaving the Malay Peninsula as a ridge 

 between them as far as the islands of Banka and Billiton. Other 

 slight changes of climate followed, when a further subsidence 

 separated these last-named islands from the Malay Peninsula, and 

 left them with two or three species which have since become 

 slightly modified. We may thus explain how it is that a species 

 is sometimes common to Sumatra and Borneo, while the inter- 

 vening island (Banka) possesses a distinct form 3 ." 



1 Geographical Distribution of Animals, vol. I. p. 359. 



2 Island Life, p. 360. 



3 As exemplified in the case of the birds of the genus Pitta. 



