and innumerable centuries.

The most important point for us, in the present connection, is
the bearing of these opposing doctrines upon the question, as
to the origin of the existing terrestrial order. On any doctrine
of uniformity that order has been evolved slowly, and, according
to law, from a pre-existing order. Any doctrine of catastrophism,
on the other hand, carries with it, by implication, the belief
that the present order of things was brought about suddenly and
irrespective of any pre-existent order; and it is important to
hold clear ideas as to which of these beliefs is the true one. In
the first place, we may postulate that the world had a beginning,
and, equally, that the existing terrestrial order had a beginning.
However far back we may go, geology does not, and cannot, reach the
actual beginning of the world; and we are, therefore, left simply
to our own speculations on this point. With regard, however, to
the existing terrestrial order, a great deal can be discovered,
and to do so is one of the principal tasks of geological science.
The first steps in the production of that order lie buried in
the profound and unsearchable depths of a past so prolonged as
to present itself to our finite minds as almost in eternity.
The last steps are in the prophetic future, and can be but dimly
guessed at. Between the remote past and the distant future, we
have, however, a long period which is fairly open to inspection;
and in saying a "long" period, it is to be borne in mind that
this term is used in its _geological_ sense. Within this period,
enormously long as it is when measured by human standards, we
can trace with reasonable certainty the progressive march of
events, and can determine the laws of geological action, by which
the present order of things has been brought about.