Travel Reference
In-Depth Information
Making some allowance for our imperfect knowledge of the Sumatran species, we see
that Java is more isolated from the two larger islands than they are from each other, thus en-
tirely confirming the results given by the distribution of birds and Mammalia, and rendering
it almost certain that the last-named island was the first to be completely separated from the
Asiatic continent, and that the native tradition of its having been recently separated from Su-
matra is entirely without foundation.
We are now enabled to trace out with some probability the course of events. Beginning at
the time when the whole of the Java sea, the Gulf of Siam, and the Straits of Malacca were
dry land, forming with Borneo, Sumatra, and Java, a vast southern prolongation of the Asi-
atic continent, the first movement would be the sinking down of the Java sea, and the Straits
of Sunda, consequent on the activity of the Javanese volcanoes along the southern extremity
of the land, and leading to the complete separation of that island. As the volcanic belt of
Java and Sumatra increased in activity, more and more of the land was submerged, till first
Borneo, and afterwards Sumatra, became entirely severed. Since the epoch of the first dis-
turbance, several distinct elevations and depressions may have taken place, and the islands
may have been more than once joined with each other or with the main land, and again sep-
arated. Successive waves of immigration may thus have modified their animal productions,
and led to those anomalies in distribution which are so difficult to account for by any single
operation of elevation or submergence. The form of Borneo, consisting of radiating moun-
tain chains with intervening broad alluvial valleys, suggests the idea that it has once been
much more submerged than it is at present (when it would have somewhat resembled
Celebes or Gilolo in outline), and has been increased to its present dimensions by the filling
up of its gulfs with sedimentary matter, assisted by gradual elevation of the land. Sumatra
has also been evidently much increased in size by the formation of alluvial plains along its
north-eastern coasts.
