hem. In our own islands, with a very few trifling
exceptions, every quadruped, bird, reptile, insect, and plant, is found
also on the adjacent continent. In the small islands of Sardinia and
Corsica, there are some quadrupeds and insects, and many plants, quite
peculiar. In Ceylon, more closely connected to India than Britain is to
Europe, many animals and plants are different from those found in India,
and peculiar to the island. In the Galapagos Islands, almost every
indigenous living thing is peculiar to them, though closely resembling
other kinds found in the nearest parts of the American continent.

Most naturalists now admit that these facts can only be 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 be 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
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