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.
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