But this question cannot he advantageously discussed, unless we take some pains to discriminate between the essential part of the uniformitarian doctrine and its accessories; and it does not appear that the Duke of Argyll has carried his studies of geological philosophy so far as this point.  For he defines uniformitarianism to be the assumption of the “extreme slowness and perfect continuity of all geological changes.”

What “perfect continuity” may mean in this definition, I am by no means sure; but I can only imagine that it signifies the absence of any break in the course of natural order during the millions of years, the lapse of which is recorded by geological phenomena.

Is the Duke of Argyll prepared to say that any geologist of authority, at the present day, believes that there is the slightest evidence of the occurrence of supernatural intervention, during the long ages of which the monuments are preserved to us in the crust of the earth?  And if he is not, in what sense has this part of the uniformitarian doctrine, as he defines it, lowered its pretensions to represent scientific truth?

As to the “extreme slowness of all geological changes,” it is simply a popular error to regard that as, in any wise, a fundamental and necessary dogma of uniformitarianism.  It is extremely astonishing to me that any one who has carefully studied Lyell’s great work can have so completely failed to appreciate its purport, which yet is “writ large” on the very title-page:  “The Principles of Geology, being an attempt to explain the former changes of the earth’s surface by reference to causes now in operation.”  The essence of Lyell’s doctrine is here written so that those who run may read; and it has nothing to do with the quickness or slowness of the past changes of the earth’s surface; except in so far as existing analogous changes may go on slowly, and therefore create a presumption in favour of the slowness of past changes.

With that epigrammatic force which characterises his style, Buffon wrote, nearly a hundred and fifty years ago, in his famous “Theorie de la Terre”:  “Pour juger de ce qui est arrive, et meme de ce qui arrivera, nous n’avons qu’a examiner ce qui arrive.”  The key of the past, as of the future, is to be sought in the present; and, only when known causes of change have been shown to be insufficient, have we any right to have recourse to unknown causes.  Geology is as much a historical science as archaeology; and I apprehend that all sound historical investigation rests upon this axiom.  It underlay all Hutton’s work and animated Lyell and Scope in their successful efforts to revolutionise the geology of half a century ago.

There is no antagonism whatever, and there never was, between the belief in the views which had their chief and unwearied advocate in Lyell and the belief in the occurrence of catastrophes.  The first edition of Lyell’s “Principles,” published in 1830, lies before me; and a large part of the first volume is occupied by an account of volcanic, seismic, and diluvial catastrophes which have occurred within the historical period.  Moreover, the author, over and over again, expressly draws the attention of his readers to the consistency of catastrophes with his doctrine.