Ch. XV.] OF THE PRIMARY ROCKS. 357 



by which they can be distinguished from each other. Nor 

 does the difficulty terminate here. It has been asserted, that 

 such veins of segregation abound in granite ; and it is like- 

 wise well known, that veins, having precisely the same appear- 

 ance, are frequently found in the slate ; and when they are 

 very numerous in a given layer, the whole collectively are 

 considered as a lode by the miner, whether they occur in a 

 schistose or granitic rock, as in the mines of Lanescot, and of 

 Balleswhidden. In fact, these depositories of ore in slate 

 are as well entitled to the name of stockworks as when 

 situated in granite. So that, we have also veins of segrega- 

 tion in slate ; and who can draw any line of demarcation be- 

 tween such veins, and the largest veins which have been 

 explored by mining operations? or, indeed, even between 

 the same description of veins which traverse both the 

 granite and the slate at the junction of these rocks ? Now 

 according to the prevailing theory, veins cannot be contem- 

 poraneous when they intersect granite and slate, because 

 these rocks are supposed to have been formed at different 

 periods; and we have heard this circumstance used as an 

 argument against the possibility of the vein being of such a 

 nature ; but surely this is not correct reasoning : the question 

 is whether they are or are not contemporaneous, without any 

 reference to the nature of the origin of the containing rock. 

 We have frequently and carefully examined numerous parallel 

 quartz-veins, running through both rocks, and differing from 

 each other in size from a mere thread of a few inches in 

 length, to a large lode extending beyond the limits of observa- 

 tion, but have not been able to detect any other distinction, 

 all bearing the same relations to the containing rock, and 

 exhibiting the same phenomena when interfered with by veins 

 which have a different course. Even Mr. Carne, though he 

 founds his distinction between true and contemporaneous 

 veins on their difference of dimensions, observes, that some 

 veins, which are very short, belong, perhaps, to the former 

 order ; and that others, of considerable length and width, to 



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