e rivers in warm climates at the present day. There is a
difference in the form of the joints of the backbone, and in some
minor particulars, between the crocodiles of the present epoch and
those which lived before the chalk; but, in the cretaceous epoch, as I
have already mentioned, the crocodiles had assumed the modern type of
structure. Notwithstanding this, the crocodiles of the chalk are not
identically the same as those which lived in the times called "older
tertiary," which succeeded the cretaceous epoch; and the crocodiles of
the older tertiaries are not identical with those of the newer
tertiaries, nor are these identical with existing forms. I leave open
the question whether particular species may have lived on from epoch
to epoch. But each epoch has had its peculiar crocodiles; though all,
since the chalk, have belonged to the modern type, and differ simply
in their proportions and in such structural particulars as are
discernible only to trained eyes.

How is the existence of this long succession of different species of
crocodiles to be accounted for?

Only two suppositions seem to be open to us--either each species of
crocodile has been specially created, or it has arisen out of some
pre-existing form by the operation of natural causes.

Choose your hypothesis; I have chosen mine. I can find no warranty for
believing in the distinct creation of a score of successive species of
crocodiles in the course of countless ages of time. Science gives no
countenance to such a wild fancy; nor can even the perverse ingenuity
of a commentator pretend to discover this sense, in the simple wrords
in which the writer of Genesis records the proceeding of the fifth and
sixth days of the Creation.

On the other hand, I see no good reason for doubting the necessary
alternative, that all these varied species have been evolved from
pre-existing crocodilian forms by the operation of causes as
completely a part of the common order of nature as those which have
effected the changes of the inorganic world.

Few will venture to affirm that the reasoning which applies to
crocodiles loses its force among other animals or among plants. If one
series of species has come into existence by the operation of natural
causes, it seems folly to deny that all may have arisen in the same
way.

* * * * *

A small beginning has led us to a great ending. If I were to put the
bit of chalk with which we started