ountain
chains; and may be found perched up, in some cases, many thousand feet
high upon their flanks. And evidence of equal cogency demonstrates that,
though, in Norfolk, the forest-bed rests directly upon the chalk, yet
it does so, not because the period at which the forest grew immediately
followed that at which the chalk was formed, but because an immense
lapse of time, represented elsewhere by thousands of feet of rock, is
not indicated at Cromer.

I must ask you to believe that there is no less conclusive proof that a
still more prolonged succession of similar changes occurred, before the
chalk was deposited. Nor have we any reason to think that the first term
in the series of these changes is known. The oldest sea-beds preserved
to us are sands, and mud, and pebbles, the wear and tear of rocks which
were formed in still older oceans.

But, great as is the magnitude of these physical changes of the world,
they have been accompanied by a no less striking series of modifications
in its living inhabitants.

All the great classes of animals, beasts of the field, fowls of the air,
creeping things, and things which dwell in the waters, flourished upon
the globe long ages before the chalk was deposited. Very few, however,
if any, of these ancient forms of animal life were identical with those
which now live. Certainly not one of the higher animals was of the same
species as any of those now in existence. The beasts of the field, in
the days before the chalk, were not our beasts of the field, nor the
fowls of the air such as those which the eye of men has seen flying,
unless his antiquity dates infinitely further back than we at present
surmise. If we could be carried back into those times, we should be as
one suddenly set down in Australia before it was colonized. We should
see mammals, birds, reptiles, fishes, insects, snails, and the like,
clearly recognisable as such, and yet not one of them would be just the
same as those with which we are familiar, and many would be extremely
different.

From that time to the present, the population of the world has undergone
slow and gradual, but incessant changes. There has been no grand
catastrophe--no destroyer has swept away the forms of life of one
period, and replaced them by a totally new creation; but one species
has vanished and another has taken its place; creatures of one type of
structure have diminished, those of another have increased, as time has
passed on. And