FORMATION OF METALLIC ORES. 



295 



causes in producing this variation. Perhaps metallic matter was dif- 

 fused through different rocks according to their elective affinity, and 

 separated from them by voltaic electricity, the different sides of the 

 vein possessing different stales of electricity; or, the strata may act 

 like a series of plates in the vohaic pile, separating and secreting me- 

 tallic matter from its different combinations. Some of the metals 

 and other substances found in veins, are capable of solution in hydro- 

 gen gas, and perhaps all of them may be so by natural processes ; 

 in this state they may have penetrated the vein, and deposited their 

 contents. 



The discovery of the metallic nature of the very earths of which 

 rocks are composed, and the probability that the metals themselves 

 are compound substances of which hydrogen forms a part, open new 

 views respecting the formation of metallic matter by natural process- 

 es, which may be within the reach of human power to develop, if not 

 to imitate. 



If metallic matter be now forming in mines, the process of its for- 

 mation is extremely slow; but there are circumstances which appear 

 to prove that it may, in some instances, be perceived. M. Trebra, 

 director of the mines in Hanover, informed a gentleman of my ac- 

 quaintance, that he had seen a leather thong suspended from the roof 

 of a mine, coated with silver: he has also observed native silver, and 

 vitreous silver ore, coating the wooden supports left in a mine called 

 Dreyweiber, in the district of Marienburgh, which had been under 

 water two hundred years, and was opened in 1777. 



From his own observations on mines, M. Trebra was led to infer^ 

 that metallic ores are formed by mineral exhalations, or were once 

 in a gaseous stale. Mr. Westgarth Forster, a practical miner in 

 Northumberland, states, that at Wolfclough mine, in the county of 

 Durham, which was closed for more than twenty years, and opened 

 again, needles of white lead ore, more than two inches in length, 

 were observed projecting from the walls. 



These and other phenomena observable in mines, may convince 

 us, that there are processes going on at present in the great labora- 

 tory of the earth, and perhaps there are analogous processes taking 

 place in the atmosphere, which may throw some light on these hid- 

 den operations of nature. The formation of saline matter on the 

 surface of walls, is a fact which merits more attention than it has 

 hitherto received. Dr. Kidd, of Oxford, has published some very 

 ingenious observations and experiments on the spontaneous produc- 

 tion of nitre on limestone, whicli may lead to more important results 

 than the learned Professor appears to have anticipated. These ex- 

 periments show, that neither the alkali nor the acid exis.ts previously 

 in the stone. Nor do they exist, ready formed, in the moisture of 

 the atmosphere, dry frosty weather being particularly favorable to 

 the rapid production of nitre, and moist weather the contrary. 



