Travel Reference
In-Depth Information
differences between us, to him undoubtedly belongs the merit of first indicating the division
of the Archipelago into an Australian and an Asiatic region, which it has been my good for-
tune to establish by more detailed observations.
Contrasts in Natural Productions
To understand the importance of this class of facts, and its bearing upon the former distribu-
tion of land and sea, it is necessary to consider the results arrived at by geologists and natur-
alists in other parts of the world.
It is now generally admitted that the present distribution of living things on the surface of
the earth is mainly the result of the last series of changes that it has undergone. Geology
teaches us that the surface of the land and the distribution of land and water is everywhere
slowly changing. It further teaches us that the forms of life which inhabit that surface have,
during every period of which we possess any record, been also slowly changing.
It is not now necessary to say anything about
how
either of those changes took place; as
to that, opinions may differ; but as to the fact that the changes themselves
have
occurred,
from the earliest geological ages down to the present day, and are still going on, there is no
difference of opinion. Every successive stratum of sedimentary rock, sand, or gravel, is a
proof that changes of level have taken place; and the different species of animals and plants,
whose remains are found in these deposits, prove that corresponding changes did occur in
the organic world.
Taking, therefore, these two series of changes for granted, most of the present peculiarit-
ies and anomalies in the distribution of species may be directly traced to them. 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 indi-
genous 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
