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XXXlll*.— Notice of a Letter from Robert Were Fox, Esq., to Sir 

 Charles Lemon, Bart., F.G.S., relative to the Origin of Mineral 

 Veins*. 



[Read April 5, 1838.] 



It can scarcely be doubted, I think, that not only the mechanical deposits in 

 mineral veins, but part, also, of those which are not mechanical, have been 

 derived from the contiguous rocks or strata. It appears to me, however, that 

 there has been another source from whence the latter may have been accumu- 

 lated in almost indefinite quantities. I refer to the deeper parts of the ori- 

 ginal fissures in which the water, at a very high temperature and pressure, 

 must have acted with great energy as a solvent, and become more or less 

 charged with earthy and metallic salts; and ascending, under these circum- 

 stances, through the upper and cooler portions of the same fluid in the fis- 

 sures, it naturally there produced deposits, in consequence of evaporation, re- 

 duction of temperature, and electrical agency. The circulation of upward 

 and downward currents of water in the fissures must thus have continued until 

 checked or superseded by too great an accumulation of diff'erent substances 

 in the latter. The silicious deposits observed in the Geyser, and many other 

 thermal springs, may be cited as examples of this kind of action. 



The circulation of the water must, moreover, have had some influence in 

 wearing away portions of the sides or walls of the fissures, and may have con- 

 tributed to produce the smoothness for which they are sometimes so remark- 

 able. The hanging walls, it may be presumed, were most exposed to the 

 action of the ascending currents, and the foot walls to that of the descending 

 ones ; but I am not prepared to say whether or not such indications or distinc- 

 tions are discoverable in mineral veins. The water-worn stones, which are 

 occasionally met with in veins, may probably be referred to this cause. 



I think it is evident that the arrangement of the ores, &c. in different 

 rocks cannot be attributed to simple chemical affinity only, because the accu- 

 mulation of the metallic masses is not found to depend merely on the nature of 

 the containing rock ; the ore of a given metal being sometimes found in 



* Mr. Fox's first communication on tliis subject, which was read before the Society, was 

 dated 19th March, 1836. See Geological Proceedings, vol. ii. p. 406. 



