attle of
Hastings. The ancestors of _Terebratulina caput serpentis_ may have
been present at a battle of Ichthyosauria in that part of the sea
which, when the chalk was forming, flowed over the site of Hastings.
While all around has changed, this Terebratulina has peacefully
propagated its species from generation to generation, and stands to
this day as a living testimony to the continuity of the present with
the past history of the globe.

* * * * *

Up to this moment I have stated, so far as I know, nothing but
well-authenticated facts, and the immediate conclusions which they
force upon the mind.

But the mind is so constituted that it does not willingly rest in
facts and immediate causes, but seeks always after a knowledge of the
remoter links in the chain of causation.

Taking the many changes of any given spot of the earth's surface, from
sea to land, and from land to sea, as an established fact, we cannot
refrain from asking ourselves how these changes have occurred. And
when we have explained them--as they must be explained--by the
alternate slow movements of elevation and depression which have
affected the crusts of the earth, we go still further back, and ask,
Why these movements?

I am not certain that any one can give you a satisfactory answer to
that question. Assuredly I cannot. All that can be said for certain
is, that such movements are part of the ordinary course of nature,
inasmuch as they are going on at the present time. Direct proof may be
given, that some parts of the land of the northern hemisphere are at
this moment insensibly rising and others insensibly sinking; and there
is indirect but perfectly satisfactory proof, that an enormous area
now covered by the Pacific has been deepened thousands of feet since
the present inhabitants of that sea came into existence.

Thus there is not a shadow of a reason for believing that the
physical changes of the globe, in past times, have been effected by
other than natural causes.

Is there any more reason for believing that the concomitant
modifications in the forms of the living inhabitants of the globe have
been brought about in any other ways?

Before attempting to answer this question, let us try to form a
distinct mental picture of what has happened in some special case.

The crocodiles are animals which, as a group, have a very vast
antiquity. They abounded ages before the chalk was deposited; they
throng th