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.

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 our mountain-chains, the courses of our rivers, and the soundings of our oceans, are not things primordially arranged in the construction of our globe, but results of successive and complex actions on a former state of things; that, again, of similar actions on another still more remote; and so on, till the original and really permanent state is pushed altogether out of sight and beyond the reach even of imagination; while on the other hand, a similar, and, as far as we can see, interminable vista is opened out for the future, by which the habitability of our planet is secured amid the total abolition on it of the present theatres of terrestrial life.”