TWO ANTAGONIST DOCTRINES OF GEOLOGY. 593 



In truth, we know causes only by their effects ; and in order to 

 learn the nature of the causes which modify the earth, we must study 

 them through all ages of their action, and not select arbitrarily the 

 period in which we live as the standard for all other epochs. The 

 forces which have produced the Alps and Andes are known to us by 

 experience, no less than the forces which have raised Etna to its pre- 

 sent height ; for we learn their amount in both cases by their results. 

 Why, then, do we make a merit of using the latter case as a measure 

 for the. former ? Or how can we know the true scale of such force, 

 except by comprehending in our view all the facts which we can bring- 

 together ? 



In reality when we speak of the uniformity of nature, are we not 

 obliged to use the term in a very large sense, in order to make the 

 doctrine at all tenable ? It includes catastrophes and convulsions of a 

 very extensive and intense kind ; what is the limit to the violence 

 which we must allow to these changes ? In order to enable ourselves 

 to represent geological causes as operating with uniform energy through 

 all time, we must measure our time by long cycles, in which repose 

 and violence alternate ; how long may we extend this cycle of change, 

 the repetition of which we express by the word uniformity ? 



And why must we suppose that all our experience, geological as 

 well as historical, includes more than one such cycle ? Why must 

 we insist upon it, that man has been long enough an observer to obtain 

 the average of forces which are changing through immeasurable time ? 



now in progress." In the sixth edition, in that which is, I presume, the cor- 

 responding passage, althoiigh it is transferred from the fourth to the first Book 

 (B. i. c. xiii. p. 325) he recommends, instead, "an earnest and patient inquiry 

 how far geological appearances are reconcileable with the effect of changes 

 now in progress." But while Mr. Lyell has thus softened the advocate's charac- 

 ter in his language in this passage, the transposition which I have noticed 

 appears to me to have an opposite tendency. For in the former edition, the 

 causes now in action were first described in the second and third Books, and 

 the great problem of Geology, stated in the first Book, was attempted to be 

 solved in the fourth. But by incorporating this fourth Book with the first, 

 and thus prefixing to the study of existing causes arguments against the belief 

 of their geological insufficiency, there is an appearance as if the author wished 

 his reader to be prepared by a previous pleading against the doctrine of cata- 

 strophes, before he went to the study of existing causes. The Doctrines of Cata- 

 strophes and of Uniformity, and the other leading questions of the Palzetiologi- 

 cal Sciences, are further discussed in the Philosophy of the Inductive Sciences 

 Book x.] 



VOL. II. 38. 



