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 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