Such
Facts Point To Changes Of Land And Sea On A Large Scale, And At A
Rate Which, Measured By The Time Required For A Change Of
Species, Must Be Termed Rapid.
By speculating on such changes, we
may easily see how partial waves of immigration may have entered
New Guinea, and how all trace of their passage may have been
obliterated by the subsequent disappearance of the intervening
land.
There is nothing that the study of geology teaches us that is
more certain or more impressive than the extreme instability of
the earth's surface. Everywhere beneath our feet we find proofs
that what is land has been sea, and that where oceans now spread
out has once been land; and that this change from sea to land,
and from land to sea, has taken place, not once or twice only,
but again and again, during countless ages of past time. Now the
study of the distribution of animal life upon the present surface
of the earth, causes us to look upon this constant interchange of
land and sea - this making and unmaking of continents, this
elevation and disappearance of islands - as a potent reality,
which has always and everywhere been in progress, and has been
the main agent in determining the manner in which living things
are now grouped and scattered over the earth's surface. And when
we continually come upon such little anomalies of distribution as
that just now described, we find the only rational explanation of
them, in those repeated elevations and depressions which have
left their record in mysterious, but still intelligible
characters on the face of organic nature.
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