Cuba,
Separated From Yucatan By A Wider And Deeper Strait, Differs More
Markedly, So That Most Of Its Productions Are
Of distinct and
peculiar species; while Madagascar, divided from Africa by a deep
channel three hundred miles wide, possesses so
Many peculiar
features as to indicate separation at a very remote antiquity, or
even to render it doubtful whether the two countries have ever
been absolutely united.
Returning now to the Malay Archipelago, we find that all the wide
expanse of sea which divides Java, Sumatra, and Borneo from each
other, and from Malacca and Siam, is so shallow that ships can
anchor in any part of it, since it rarely exceeds forty fathoms
in depth; and if we go as far as the line of a hundred fathoms,
we shall include the Philippine Islands and Bali, east of Java.
If, therefore, these islands have been separated from each other
and the continent by subsidence of the intervening tracts of
land, we should conclude that the separation has been
comparatively recent, since the depth to which the land has
subsided is so small. It is also to be remarked that the great
chain of active volcanoes in Sumatra and Java furnishes us with a
sufficient cause for such subsidence, since the enormous masses
of matter they have thrown out would take away the foundations of
the surrounding district; and this may be the true explanation of
the often-noticed fact that volcanoes and volcanic chains are
always near the sea. The subsidence they produce around them
will, in time, make a sea, if one does not already exist.
But, it is when we examine the zoology of these countries that we
find what we most require - evidence of a very striking character
that these great islands must have once formed a part of the
continent, and could only have been separated at a very recent
geological epoch. The elephant and tapir of Sumatra and Borneo,
the rhinoceros of Sumatra and the allied species of Java, the
wild cattle of Borneo and the kind long supposed to be peculiar
to Java, are now all known to inhabit some part or other of
Southern Asia. None of these large animals could possibly have
passed over the arms of the sea which now separate these
countries, and their presence plainly indicates that a land
communication must have existed since the origin of the species.
Among the smaller mammals, a considerable portion are common to
each island and the continent; but the vast physical changes that
must have occurred during the breaking up and subsidence of such
extensive regions have led to the extinction of some in one or
more of the islands, and in some cases there seems also to have
been time for a change of species to have taken place. Birds and
insects illustrate the same view, for every family and almost
every genus of these groups found in any of the islands occurs
also on the Asiatic continent, and in a great number of cases the
species are exactly identical. Birds offer us one of the best
means of determining the law of distribution; for though at first
sight it would appear that the watery boundaries which keep out
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 and New Guinea as the Western Islands do to Asia. It is
well known that the natural productions of Australia differ from
those of Asia more than those of any of the four ancient quarters
of the world differ from each other. Australia, in fact, stands
alone: it possesses no apes or monkeys, no cats or tigers,
wolves, bears, or hyenas; no deer or antelopes, sheep or oxen; no
elephant, horse, squirrel, or rabbit; none, in short, of those
familiar types of quadruped which are met with in every other
part of the world.
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