8 Dr. Boase's Remarks on Mr. Hopkins's 



cognise the influence of a previously veined or jointed struc- 

 ture on the direction of its dislocations." And yet two or 

 three pages afterwards we find a different opinion, viz. that 

 the great system of metalliferous veins was formed in open 

 joints superinduced after the great dislocations which accom- 

 panied the injection of the granite. I am glad to find that 

 his " hasty inspection" of Cornwall has confirmed my more 

 lentTthened observation on the coincidence of the directions of 

 veins with those of joints; but he surely jumps too hastily to 

 the conclusion that this circumstance destroys the contempo- 

 raneous hypothesis which I have advocated. Although the 

 direction of veins may correspond with lines of structure, they 

 are not identical therewith. The joints pass indiscriminately 

 through both veins and rock, whether granite or slate, or both 

 conjointly; so that individual concretions or blocks, formed 

 by the intersection of parallel systems of joints, contain more 

 or less of these, according as the vein contracts or expands in 

 its dimensions: — ^just as the lines of structure in sedimentary 

 rocks pass through concretions and organic remains, so do 

 they traverse the granite, slate, and veins, showing in both 

 cases that the things intersected must have existed previous 

 to the consolidation of the mass. 



Mr. Hopkins regards the contemporaneous formation as 

 " an inconceivable process," more especially for those who 

 consider the slate as a sedimentary rock. Such a notion, 

 however, is not perhaps so absurd as it at first sight appears 

 to be, but is consistent with the prevailing theory ; for if the 

 primary slates be metamorphic rocks, why not the granite 

 also? Vast districts in the North of Europe and elsewhere 

 consist of gneiss, which some have called granite, and others 

 granitic gneiss. Why was it not as easy for the central fire to 

 change fossiliferous strata into granite, as into granitic gneiss? 

 And if so, then the primary slates and granite might be con- 

 temporaneous; though in this case formed by a superin- 

 duced or secondary action, whilst in the one which I advocate 

 they have resulted from the original fusion of the earth. 

 Mr. Hopkins acknowledges that " the perfect continuity of 

 the veins of Cornwall in passing from the killas to the granite 

 forms a curious feature in the geology of that district if we 

 are to regard the former as a sedimentary deposit." It cer- 

 tainly places the prevailing theory in a most perplexing di- 

 lemma, which however it appears to me is satisfactorily solved 

 by admitting the contemporaneous nature of the granite and 

 slate. 



As the metalliferous veins of Cornwall do not seem to be 



