182 ON THE MINERAL AND METALLIFEROUS |Ch. IX. 



These facts are diametrically opposed to the prevailing 

 opinion, founded on the reports of those who have written on 

 the Cornish veins. It is true, that a line drawn so as to in- 

 tersect the two extremities of these veins has a regular bear- 

 ing ; but to call such veins straight on this account, would 

 certainly not be less incorrect than to apply this term to 

 meandering rivers. 



The characters which have been already described, may 

 be considered as of a general nature, being more or less ap- 

 plicable to each individual: but we now proceed to detail 

 those phenomena which result from the interference of veins 

 with each other, occasioned by veins of a parallel course 

 dipping to opposite points of the compass, or to the same 

 point at different angles ; or by veins running in different 

 directions. 



In veins thus circumstanced, some are found to continue 

 their course uninterruptedly, so as to intersect others which 

 often terminate abruptly against the cross-vein. The detached 

 parts of the intersected veins sometimes continue their course 

 in the same direction, but, more commonly, they cannot be 

 traced in the same line, the part on the opposite side of the 

 vein being at some distance therefrom, though running in a 

 parallel direction. In short, the intersected veins exhibit 

 such an appearance as might arise from the motion of the 

 rock on one side of the cross-vein, or from movements on 

 both sides, in a contrary direction : thence, the miners have 

 attributed these occurrences to heaves and throws; and the 

 same views have been adopted by geologists. 



Now, these phenomena may be frequently observed on a 

 small scale in blocks of marble, serpentine, and other rocks ; 

 or, indeed, even in hand-specimens, the schistose rocks of 

 of Cornwall abounding in such illustrations, in which the 

 veins also often differ in mineral composition ; the intersected 

 veins being sometimes metalliferous, traversed by one or more 

 quartz-veins. In these instances, the veins are frequently 

 so small and short, and moreover so intimately united with 



