32 LeConte and Rising — Metalliferous Vein-formation 



held in solution also metallic sulphides, especially mercuric 

 sulphide : for these are found associated with the silica in such 

 wise that the two must have been deposited from the same 

 solution. Sometimes the cinnabar is embedded in the silica, 

 and risible on cutting or breaking as reddish cloudings and 



such cavities and fissures. The solvent of the cinnabar seems 



undoubtedly to have been alkaline sulphides. There has been 



rence of statement among the best chemists 



as to the solubility of most metallic sulphides in alkaline sub 

 at recent experiments have made probable at least a 

 feeble solubility, and the most recent and reliable of all, viz: 

 those of Mr. Christy* in which cinnabar was subjected to the 

 prolonged action of alkaline sulplii My imitating 



the composition of the solfataric waters of California, under 

 heavy pressure and super heat, has placed the solubility under 

 these conditions beyond all reasonable doubt. Whatever be 

 the solvent, it is evident that cooling, relief of pressure and per- 

 haps escape of H,S and CO, in the ascending waters would 

 diminish solubility and produce deposits in the water-ways. 



(c.) Pyrites. The pyrites found disseminated in the rocks at 

 all depths yet reached may (1) have been brought up from 

 below in solution in the solfataric waters and deposited like the 



or (2) may have been formed by reaction of 

 sulphides on iron-silicates of the rocks, especially mo lavns. 

 as suggested by Bunsen, in the rocks of Iceland, or finally (3) 

 may have been formed by deoxidation of iron sulphate by 

 organic matter, as we so often see elsewhere. That the first 

 method is the true one in many cases— that the iron sulphide 

 was held in solution and deposited like the cinnabar— is proved 

 not only by the fact that it occurs abundantly beneath the lava 

 in p ire sandstones free from other forms of iron, but also by the 

 fact that it is found alternating with silica and cinnabar in suc- 

 c-^ivr layers. liriimr c;ivirws, in such wise that it must have 

 been deposited from the same solution. It may have been de- 

 posited also in the other ways, but this one seems certain. f 



ol.) Sulphur. Sulphur is well known to deposit freely from 

 all springs containing excess of sulphydric acid. By contact 

 with the oxygen of the air the hydrogen of this gas is oxidized 

 and the sulphur deposited. Hence the deposit of sulphur is 

 always very superficial and quickly gives place to metallic sul- 

 phides as we go below the influence of the air. 



Thus far we have spoken only of the deposits from the up- 



