the land quadrupeds could be easily
passed over by birds, yet practically it is not so; for if we leave out
the aquatic tribes which are preeminently wanderers, it is found that
the others (and especially the Passeres, or true perching-birds, which
form the vast majority) are generally as strictly limited by straits and
arms of the sea as are quadrupeds themselves. As an instance, among the
islands of which I am now speaking, it is a remarkable fact that Java
possesses numerous birds which never pass over to Sumatra, though they
are separated by a strait only fifteen miles wide, and with islands in
mid-channel. Java, in fact, possesses more birds and insects peculiar
to itself than either Sumatra or Borneo, and this would indicate that it
was earliest separated from the continent; next in organic individuality
is Borneo, while Sumatra is so nearly identical in all its animal forms
with the peninsula of Malacca, that we may safely conclude it to have
been the most recently dismembered island.

The general result therefore, at which we arrive, is that the great
islands of Java, Sumatra, and Borneo resemble in their natural
productions the adjacent parts of the continent, almost as much as such
widely-separated districts could be expected to do even if they still
formed a part of Asia; and this close resemblance, joined with the fact
of the wide extent of sea which separates them being so uniformly and
remarkably shallow, and lastly, the existence of the extensive range of
volcanoes in Sumatra and Java, which have poured out vast quantities
of subterranean matter and have built up extensive plateaux and lofty
mountain ranges, thus furnishing a vera causa for a parallel line of
subsidence--all lead irresistibly to the conclusion that at a very
recent geological epoch, the continent of Asia extended far beyond its
present limits in a south-easterly direction, including the islands of
Java, Sumatra, and Borneo, and probably reaching as far as the present
100-fathom line of soundings.

The Philippine Islands agree in many respects with Asia and the other
islands, but present some anomalies, which seem to indicate that they
were separated at an earlier period, and have since been subject to many
revolutions in their physical geography.

Turning our attention now to the remaining portion of the Archipelago,
we shall find that all the islands from Celebes and Lombock eastward
exhibit almost as close a resemblance to Australia