432 On the Chemical Geology of the Gold-fields of California. 



which they adhered, and that a subsequent deposition of quartz 

 took place between them and the rock from which they had 

 become detached. In this way were introduced the masses of 

 rock known as "horses." 



(c) The formation of quartz veins is often due to hydrothermal 

 agencies, of which evidences are still to be found in the hot 

 springs and recent metalliferous veins to be met with in various 

 parts of the Pacific coast. 



(d) From the presence of gas-cavities and the variable tem- 

 peratures at which the vacuities in their fluid-cavities become 

 filled, it may be inferred that they are the result of an intermit- 

 tent action, and that the fissures were sometimes traversed by 

 currents of hot water, whilst at others they gave off aqueous va- 

 pour or gaseous exhalations*. 



This is precisely what is now taking place at Steamboat 

 Springs, where the formation of a vein is in progress, and from 

 which currents of boiling water are often poured forth, whilst 

 at other times the fissures only give off currents of steam and 

 heated gases. 



(e) That gold may be deposited from the same solutions which 

 give rise to the formation of the enclosing quartz, would appear 

 evident from the presence of that metal in pyrites enclosed in 

 siliceous incrustations near Borax Lake, in the semi-opal of the 

 North Star vein &c, as well as from the fact of gold having been 

 found in the interior of the stems of trees which in deep dig- 

 gings are often converted into pyrites. 



(/) The constant presence of iron pyrites in auriferous veins, 

 and when so occurring its invariably containing a certain 

 amount of gold, suggests the probability of this sulphide being 

 in some way necessarily connected with the solvent by which the 

 precious metal was held in solution. Without considerable ad- 

 dition to our present limited knowledge of the subject, it would 

 be impossible to explain the exact process by which the solution 

 of gold was effected. It has, however, been shown by Wurtzf 

 (who has since suggested the probability of ferruginous salts 

 being the means employed by nature for effecting the solution 

 of gold J) that finely divided gold is soluble in tbesesquichloride 

 of iron, and more sparingly in the sesquisulphate of that metal. 

 It is also well known that iron pyrites sometimes results from 

 the action of reducing agents on the sulphates of iron. 



* Sorby, "On the Microscopical Structure of Crystals. § 1. Crystals 

 formed from solution in water," Quarterly Journal of the Geological So- 

 ciety, vol. xiv. pp. 453-500. 



f American Journal of Science, vol. xxvi. p. 51. 



\ Memoir read before the American Association for the Advancement 

 of Science, August 1, 1866. 



