though closely resembling other kinds found in the nearest
parts of the American continent.
Most naturalists now admit that these facts can only
he explained by the greater or less.lapse of time since
the islands were upraised from beneath the ocean, or were
separated from the nearest land; and this will he generally
(though not always) indicated by the depth of the intervening
sea. The enormous thickness of many marine
deposits through wide areas shows that subsidence has
often continued (with intermitting periods of repose)
during epochs of immense duration. The depth of sea
produced by such subsidence will therefore generally be
a measure of time ; and in like manner the change which
organic forms have undergone is a measure of time.
"When we make proper allowance for the continued introduction
of new animals and plants from surrounding
countries, by those natural means of dispersal which have
been so well explained by Sir Charles Lyell and Mr.
Darwin, it is remarkable how closely these two measures
correspond. Britain is separated from the continent by
a very shallow sea, and only in a very few cases have our
animals or plants begun to show a difference from the
corresponding continental species. Corsica and Sardinia,
divided from Italy by a much deeper sea, present a much
greater difference in their organic forms. Cuba, separated
from Tucatan 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
VOL. i. c