498 



Mr. Pox on Mineral Veins. 



granite, or in " elvan," and not in " killas," and sometimes in the latter, and 

 not in either of the former. The remarkable concentration of the ores in 

 some rocks in preference to others, seems rather to have resulted from their 

 relative positions, or other circumstances of a local nature; and when I con- 

 sidered these very striking phaenomena, which everywhere occur, and the 

 actual proofs I had obtained of electrical action in many of our metallic veins, 

 I felt compelled to adopt the conclusion, that some definite agency, such as 

 electricity, must have produced or controlled those relations. My views on 

 this part of the subject, I have more fully stated in my former communication, 

 and I imagine I see more and more reason to believe that the eastward and 

 westward tendency of metallic veins may be ascribed to the electro-magnetic 

 influence of the earth. In some parts of the world there may be found consi- 

 derable deviations from this bearing, owing, perhaps, to local circumstances ; 

 but the coincidence in their direction, generally speaking, is so decided, as 

 clearly to indicate the operation of a general law. The greatest deviation in 

 this county from the prevailing strike of our metalliferous veins has been 

 supposed to exist in the tin veins of St. Just. I find, however, that their 

 course, with respect to the true meridian, is, on the average, about N.W. and 

 S.E., and that of the guides, or cross-courses, nearly north and south. 



It is worthy of remark, that many of the large veins of oxide of iron found 

 in Cornwall, Devon, and other districts, have a north and south bearing, or, 

 rather, are nearly coincident with the magnetic meridian. 



Much of the quartz in the cross courses may have been brought up in hot 

 water from a great depth, and been gradually deposited as the successive 

 portions of water became reduced in temperature. But the fibrous or crystal- 

 line texture of this quartz, with the axis of the crystals at right angles to the 

 walls of the cross courses, is often so marked and decided, as to indicate the 

 operation of some general cause or force having a definite direction*. 



* I have obtained, by means of voltaic action, many veins of sulphate of zinc in clay, having a 

 fibrous texture, perpendicular to the veins, like the quartz in cross courses, or like satin spar. 



Falmouth, 

 January 28, 1837. 



