" Researches in Physical Geology." 9 



referrible to the same cause as those of Flintshire and Derby- 

 shire, Mr. Hopkins has sought for some other mode of ob- 

 taining fissures in which they might be formed ; and he thinks 

 that such may be found in the structural joints of the granite 

 and slate produced since the elevatory injection of the granite. 

 But before admitting this, let us inquire whether such a for- 

 mation in joints would be analogous to the metalliferous veins 

 of Cornwall. Existing joints removed from atmospheric 

 agency are merely linear*, whilst the veins ai'e of all dimen- 

 sions from a line to even thirty feet in thickness. How few 

 joints comparatively have veins ; and how frequently both the 

 rock and vein possess structural joints in common ! Again, 

 what proof is there that the Cornish slate was not constituted 

 like all other solid rocks which we now find endowed with 

 joints, whether horizontal or inclined ? Even Mr. Hopkins 

 admits that these joints have arisen from molecular action, 

 and are consequently independent of the origin or the posi- 

 tion of the unconsolidated rock. 



Before concluding I embrace this opportunity, as imme- 

 diately connected with the foregoing subject, to notice a pas- 

 sage in Mr. Lyell's address to the Geological Society con- 

 cerning my comments on Professor Sedgwick's paper on the 

 structure of rocks. He observes that I consider certain pas- 

 sages in this paper inconsistent with each other, and he con- 

 fesses that at first they struck him in the same light, but that 

 the Professor has explained the apparent inconsistency. Now 

 the tendency of this remai'k of the President of the Geologi- 

 cal Society is to imply that I am equally mistaken, and though 

 this is only one of many points which I have discussed, yet ail 

 may fall under the same imputation. The haste consequent on 

 preparing for an annual meeting may account for the oversight, 

 but the fact is, that the Professor's reply to Mr. Lyell is no 

 explanation, but merely a repetition of the statement which is 

 as clearly expressed in the paper itself, and which I have en- 

 deavoured to show cannot be maintained. This being so, 

 and the examples brought forward by the President being 

 also opposed to the Professor's hypothesis, perhaps he may 

 be induced to give the case a more careful consideration. 



* Since writing tlie above I have learnt that Mr. Robert Were Fox has 

 advanced a new opinion concerning the Ibrination of veins — on the sup- 

 position of a gradual contraction of the mass producing a progressive en- 

 largement of joints. 



Tliird Series. Vol.9. No. 51. ,/?//// 18 3G. 



