chap, xii.] THE ORIENTAL REGION. 357 



unchanged, the characteristics which had been developed under 

 nearly identical conditions when the great island formed part 

 of the continent. Geology teaches us that similar changes in 

 the forms of the higher vertebrates have taken place during the 

 Post-Tertiary epoch ; and there are other reasons for believing 

 that, under such conditions of isolation as in Banca, the 

 change may have required but a very moderate period, even 

 reckoned in years. We will now return to the more difficult 

 problem presented by the peculiar continental relations of Java, 

 as already detailed. 



Probable Recent Geographical Changes in the Indo-Malay 

 Islands. — Although Borneo is by far the largest of the Indo- 

 Malay islands, yet its physical conformation is such that, were 

 a depression to occur of one or two thousand feet, it would be 

 reduced to a smaller continuous area than either Sumatra or 

 Java. Except in its northern portion it possesses no lofty 

 mountains, while alluvial valleys of great extent penetrate fai 

 into its interior. A very moderate depression, of perhaps 500 

 feet, would convert it into an island shaped something like Cele- 

 bes ; and its mountains are of so small an average elevation, and 

 consist so much of isolated hills and detached ranges, that a 

 depression of 2,000 feet would almost certainly break it up into 

 a group of small islands, with a somewhat larger one to the 

 north. Sumatra (and to a less extent Java) consists of an almost 

 continuous range of lofty mountains, connected by plateaus from 

 3,000 to 4,000 feet high ; so that although a depression of 2,000 

 feet would greatly diminish their size, it would probably leave 

 the former a single island, while the latter would be separated 

 into two principal islands of still considerable extent. The en- 

 ormous amount of volcanic action in these two islands, and the 

 great number of conical mountains which must have been slowly 

 raised, chiefly by ejected matter, to the height of 10,000 and 

 12,000 feet, and whose shape indicates that they have been for- 

 med above water, renders it almost certain that for long periods 

 they have not undergone submersion to any considerable extent. 

 In Borneo, however, we have no such evidences. No volcano, 



