- To Understand The Importance
Of This Class Of Facts, And Its Bearing Upon The Former
Distribution Of Land And Sea, It Is Necessary To Consider The
Results Arrived At By Geologists And Naturalists 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 peculiarities 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.
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