83 SIXTH REPORT — 183G. 



most exposed to the action of ferruginous matter, as indicated by 

 the gossan, and of waters holding salts in solution. The gossan of 

 the Cnrnish miners is a sort of iron ochre, which usually abounds in 

 copper veins, but not in those of tin, and Mr. Fox obtained a substance 

 closely resembling it by substituting a solution of the sulphate of iron 

 for the sulphate of copper. He likewise mentioned his having found 

 that when the muriate of tin in solution was placed in a voltaic circuit, 

 apart of the tin accumulated at the negative pole in a metallic state, and 

 the remainder at the positive pole in the state of a peroxide, the same 

 as it exists in the mines, and he considered that this experiment is cal- 

 culated to explain why tin and copper ores so commonly occur in dif- 

 ferent veins, or in different parts of the same vein. 



He alluded to a paper of his which had been read before the Geological 

 Society, in which he referred the definite arrangement of the ores in 

 different rocks to voltaic agency, and assumed that the fact of veins being 

 often found productive of ore in one rock and barren in another might 

 be due to the relative electrical states of those rocks when the deposi- 

 tions took place, and he conceived that the prevalence of different salts 

 in solution in the minute fissures of different rocks might, amongst 

 other causes, have tended to generate voltaic currents. The water 

 taken from the mines which he had examined differed exceedingly in 

 the nature and proportions of the saline matter which it contained ; and 

 he had obtained considerable voltaic action by the influence of different 

 ores on each other, such, for instance, as a piece of yellow, and another 

 of grey copper ore, separated by clay which was moistened with water 

 taken from the same mine as the ores were. 



Mr. Fox thought that the prevailing direction of metalliferous veins 

 might be connected with that of magnetic forces ; the former is nearly at 

 right angles to the present magnetic meridian. He moreover stated his 

 reasons for thinking that the phsenomena of the intersections of some 

 veins by others are not incompatible with the contemporaneous forma- 

 tion of the original fissures in opposite directions, on the hypothesis of 

 their having undergone a progressive opening ; and he considered that 

 the proofs of such progressive opening abounded in the Cornish lodes 

 and cross courses, the larger veins being commonly divided into smaller 

 parallel veins, having walls resembling the outer walls, between which 

 all were included. Thus he supposed that tin veins were intersected 

 by copper veins in consequence of the latter being less hard than the 

 former, and containing in general more clay and other mechanical 

 deposits, whilst cross courses have still more of such mechanical de- 

 posits, and intersect both tin and copper veins ; for if we suppose such 

 veins, nearly at right angles to each other, to be cracked or further 

 opened, it is evident that the rent in the metallic vein might be rapidly 

 filled up with clay or other matter conveyed into it by the water circu- 

 lating in the veins. 



