We Are Now Able 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 Asiatic 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, until first Borneo, and afterwards Sumatra, became
entirely severed. Since the epoch of the first disturbance,
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 separated. 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
mountain 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.
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