CHAP. XII. ] THE ORIENTAL REGION. 307 
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 far 
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, 
