ti 



' 



ON MINERAL VEINS. 385 



or universal. Yet this doctrine is supported by geo- 

 logists who imagine that the mines of New Spain are 

 similar to those of Hungary and Saxony. That Patrin, 

 who imagined the earth organized and endowed with 

 a vital principle, should protract a zone of copper, 

 silver, and lead, from England through Europe, Asia? 

 and America, is consistent. 



Of the Seats and the Contents of Mineral 

 Feins. 



The nature of the rocks in which mineral veins 

 are found, is an obvious object of inquiry, but it can- 

 not be converted to any useful purposes. They may 

 be said rather to belong to countries than to rocks; 

 since, in one, that substance may be highly productive 

 of veins and metals, which, in another, is deficient and 

 barren. They are, however, most abundant in the 

 primary or antient rocks, and are also more common 

 in gneiss, micaceous schist, and argillaceous schist, 

 than in granite or in the older porphyries. In the 

 secondary, or recent strata, they occur chiefly in the 

 lowest, as in the mountain limestone, and are scarcely 

 found in the upper strata, or above coal. In the same 

 manner they are rare in the later trap rocks; but if 

 Hacquet's observations are correct, they occur at 

 Nagyag, either in these, or in antient volcanic 

 rocks. 



In the primary rocks, they are sometimes found at 

 the junctions of granite with the strata, as happens in 

 Cornwall and at Strontian. But no practical advan- 

 tages accrue from any thing yet known on this subject; 

 unless under experience acquired in particular dis- 

 tricts. The limitation of Tin to Cornwall and a few 

 iher spots, and its exclusion from countries formed 



VOL. i. c t 



