Such is the past history of the globe, as sketched for us, in alternating scenes of fruitful peace and revolutionary destruction, by the earlier geologists.  As before said, we cannot wonder at the former general acceptance of Catastrophistic doctrines.  Even in the light of our present widely-increased knowledge, the series of geological monuments remains a broken and imperfect one; nor can we ever hope to fill up completely the numerous gaps with which the geological record is defaced.  Catastrophism was the natural method of accounting for these gaps, and, as we shall see, it possesses a basis of truth.  At present, however, catastrophism may be said to be nearly extinct, and its place is taken by the modern doctrine of “Continuity” or “Uniformity”—­a doctrine with which the name of Lyell must ever remain imperishably associated.

The fundamental thesis of the doctrine of Uniformity is, that, in spite of all apparent violations of continuity, the sequence of geological phenomena has in reality been a regular and uninterrupted one; and that the vast changes which can be shown to have passed over the earth in former periods have been the result of the slow and ceaseless working of the ordinary physical forces—­acting with no greater intensity than they do now, but acting through enormously prolonged periods.  The essential element in the theory of Continuity is to be found in the allotment of indefinite time for the accomplishment of the known series of geological changes.  It is obviously the case, namely, that there are two possible explanations of all phenomena which lie so far concealed in “the dark backward and abysm of time,” that we can have no direct knowledge of the manner in which they were produced.  We may, on the one hand, suppose them to be the result of some very powerful cause, acting through a short period of time.  That is Catastrophism.  Or, we may suppose them to be caused by a much weaker force operating through a proportionately prolonged period.  This is the view of the Uniformitarians.  It is a question of energy versus time and it is time which is the true element of the case.  An earthquake may remove a mountain in the course of a few seconds; but the dropping of the gentle rain will do the same, if we extend its operations over a millennium.  And this is true of all agencies which are now at work, or ever have been at work, upon our planet.  The Catastrophists, believing that the globe is but, as it were, the birth of yesterday, were driven of necessity to the conclusion that its history had been checkered by the intermittent action of paroxysmal and almost inconceivably potent forces.  The Uniformitarians, on the other hand, maintaining the “adequacy of existing causes,” and denying that the known physical forces ever acted in past time with greater intensity than they do at present, are, equally of necessity, driven to the conclusion that the world is truly in its “hoary eld,” and that its present state is really the result of the tranquil and regulated action of known forces through unnumbered and innumerable centuries.