r 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.

The natural belief on this subject doubtless is, that the world,
such as we now see it, possessed its present form and configuration
from the beginning. Nothing can be more natural than the belief
that the present continents and oceans have always been where
they are now; that we have always had the same mountains and
plains; that our rivers have always had their present courses,
and our lakes their present positions; that our climate has always
been the same; and that our animals and plants have always been
identical with those now familiar to us. Nothing could be more
natural than such a belief, and nothing could be further removed
from the actual truth. On the contrary, a very slight acquaintance
with geology shows us, in the words of Sir John Herschel, that
"the actual configuration of our continents and islands, the
coast-lines of our maps, the direction and elevation of