386 ON MINERAL VEINS. 



of the same materials, the barrenness of gneiss in 

 Scotland, compared with its fertility in Saxony, may 

 be added to a thousand other instances, to prove that 

 we must be content to possess mines wherever they 

 are found, without wasting our means where we have 

 no evidences of their existence. That much false 

 philosophy should have been adopted on the subject 

 of mines, is a natural consequence of that perversion 

 of judgment which so often attends the pursuit of 

 wealth, and is produced by examples of its sudden 

 acquisition. 



The contents of mineral veins are various; and 

 though the metals form the most valuable of those, 

 they bear a very small proportion to the rest. No 

 general rules respecting these contents can be given, 

 as they vary in almost every country, in every vein, 

 and often, in every part of a vein. It is common, 

 however, to find that the sides next to the including 

 rocks are formed of earthy matters ; sometimes of 

 clay, at others of quartz, and, not unfrequently, of 

 fragments of the including rocks, united by crystalline 

 and earthy substances; while the rock is generally 

 decomposed and altered at its junction with the vein, 

 as detached fragments of it are sometimes also in- 

 cluded within that. This occurrence has sometimes 

 presented an interesting variation, where a vein traver- 

 sing schist and granite together, has contained frag- 

 ments of the former within the space bounded by the 

 latter, arid the reverse. This fact seems to prove 

 revolutions of a mechanical nature in the vein, either 

 at the time, or after the period, of its formation. 



I need not enumerate all the earthy minerals which 

 have been found in veins, but the most common are 

 quartz, calcareous spar, barytes and fluor. These, 

 like the metallic substances, occur in different parts 



