Sir A. Geiliie—Acjc of the Earth. 455 



wei*e precerlecl by others which we know must have existed, though 

 no vestige ut them may remain. 



It may be further asserted that, while it was Hutton who first 

 impressed on modern geology the conviction that for the adequate 

 comprehension of the past history of the earth vast periods of time 

 must be admitted to have elapsed, our debt of obligation to him is 

 increased by the genius with which he linked the passage of these 

 vast periods with the present economy of nature. He first realized 

 the influence of time as a factor in geological dynamics, and first 

 taught the efficacy of the quiet and unobtrusive forces of nature. 

 His predecessors and contemporaries were never tired of invoking 

 the more vigorous manifestations of terrestrial energy. They saw- 

 in the composition of the land and in the structure of mountains and 

 valleys memorials of numberless convulsions and cataclysms. In 

 Hutton's philosophy, however, "it is the little causes, long continued, 

 which are considered as bringing about the greatest changes of 

 the earth." i 



And yet, unlike many of those who derived their inspiration from 

 his teaching, but pushed his tenets to extremes which he doubtless 

 never anticipated, he did not look upon time as a kind of scientific 

 fetich, the invocation of which would endow with efficacy even the 

 most trifling phenomena. As if he had foreseen the use that might 

 be made of his doctrine, he uttered this remarkable warning : 

 " With regard to the eftect of time, though the continuance of time 

 may do much in those operations which are extremely slow, where 

 no change, to our observation, had appeared to take place, yet, 

 where it is not in the nature of things to produce the change in 

 question, the unlimited course of time would be no more efi"ectual 

 than the moment by which we measure events in our observations." ^ 



We thus see that in the philosophy of Hutton, out of which so 

 much of modern geology has been developed, the vastness of the 

 antiquity of the globe was deduced from the structure of the terres- 

 trial crust and the slow rate of action of the forces by which the 

 surface of the crust is observed to be modified. But no attempt was 

 made by him to measure that antiquity by any of the chronological 

 standards of human contrivance. He was content to realize for 

 himself and to impress upon others that the history of the earth could 

 not be understood, save by the admission that it occupied prolonged 

 though indeterminate ages in its accomplishment. And assuredly 

 no part of his teaching has been more amply sustained by the 

 subsequent progress of research. 



Playfair, from whose admirable "Illustrations of the Huttonian 

 Theory " most geologists have derived all that they know directly 

 of that theory, went a little further than his friend and master in 

 dealing with the age of the earth. Not restricting himself, as Hutton 

 did, to the testimony of the rocks, which showed neither vestige of 

 a beginning nor prospect of an end, he called in the evidence of 

 the cosmos outside the limits of our planet, and declared that in 



1 " Theory of the Earth," vol. ii, p. 205. 



2 Op. cit., vol. i, p. 44. 



