i 
+ Joseph LeConte—Genesis of Metalliferous Ves. 
under pressure and super-heat by actual experiment; and these 
are among the most insoluble of metallic sulphides. 
It is certain, then, that metallic sulphides are soluble to a 
limited extent in alkaline sulphides forming doubtless double 
sulphides. It is certain also that the solubility is increased by 
superheat and pressure. It is therefore also certain that hot 
waters containing alkaline carbonates and alkaline sulphides, 
circulating at great depth and therefore under heavy pressure, 
would take up silica, earthy and metallic carbonates, and me- 
tallic sulphides, and that coming up slowly toward the surface 
they would deposit these substances in theirr courses, partly 
by cooling and partly by relief of pressure, and thus form 
metalliferous veins. 
e have given what seems to be the most usual cause of 
deposit, viz: cooling and relief of pressure; but this is prob- 
ably not the only cause, There are many chemical reactions 
by which the same result may be attained. We will mention 
only the more obvious of these. (a) Organic matters are of 
almost universal occurrence in subterranean waters, and their 
agency in reducing metallic oxides and metallic salts is well 
own. e more we study the chemistry of nature, the more 
we are impressed with the importance of organic matter as a 
universal reducing agent. Organic matter in form of hydro- 
carbons is almost invariably found in connection with cinnabar. 
Its agency in reducing iron sulphate to sulphide is seen every- 
where. It is not improbable therefore that organic matter cir- 
culating in the same solution with metallic sulphates may be a 
frequent means of reducing these and depositing them as metal- 
lic sulphides. (0.) Again: alkaline carbonate and sulphide 
waters, dissolving silica and metallic sulphides and coming in 
contact in their course with decomposing organic matters, may 
be neutralized by the acids of organic decomposition and thus 
compelled to deposit their freight. This apparently takes in 
deep hydraulic mines in the silicification of wood and possibly 
in the deposit of iron sulphide. (c.) Lastly: it is possible that 
in some cases water from different sides and carrying different 
malaria may meet in the same fissure and deposit by reaction. 
sulphide on iron sulphate. If this reaction had taken place 
sufic iently slowly, it is possible that we sulphide would have 
been crystalline. All these methods and perhaps many others 
not yet imagined may occur; but the first, viz: i cooling and 
relief of pressure is probably of most universal Bis (aati 
