0HAP.I.] PHYSICAL GEOGRAPHY. 15
of life which inhabit that surface have, during every
period of which we possess any record, been also slowly
changing.
It is uot 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. 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,