of the Gold-fields of California. 431 



quantities of fossil wood, and are often hardened into a compact 

 conglomerate by a cement consisting either of finely crystallized 

 iron pyrites or of silica. This iron pyrites encloses gold which 

 is sometimes water- worn, and at others is in a crystalline or fili- 

 form state, showing that it has not been subjected to attrition. 

 In Australia, pyrites replacing the woody constituents of the 

 stems of trees found in similar positions has been shown by va- 

 rious chemists to contain large quantities of the precious metal. 

 The siliceous cement of the ancient river-beds of California has 

 sometimes, but rarely, been deposited in a crystalline form, and 

 on examination such crystals have not been found to contain 

 fluid-cavities presenting the usual vacuities. 



(7) Mineral springs are exceedingly numerous, and their 

 waters generally escape from the ground in a state of ebullition. 

 These springs deposit silica, sulphur, iron pyrites, &c, whilst 

 in some instances cinnabar is brought to the surface in large 

 quantities by solfatara action ; occasionally the deposited silica 

 takes the form of an ordinary auriferous vein, and gold is stated 

 on good authority to have been found in quartz so produced. 

 At the surface the silica of such deposits contains a larger amount 

 of water than that of the older quartz veins of the country, but 

 appears gradually to lose it, and, although generally amorphous, 

 is sometimes met with in a crystallized state. 



(8) In the districts abounding in mineral springs are lakes 

 of which the waters are highly alkaline, and which, in addition 

 to carbonates and sulphate of soda, contain large quantities of 

 chloride of sodium. These have no visible outlets, and act as 

 vast evaporating-pans, in which the waters of the various streams 

 flowing into them are being concentrated by the action of the 

 sun's rays. The incrustations deposited on the shores of Owen's 

 Lake contain a much larger proportion of carbonate of soda than 

 the salts obtained by direct evaporation of the lake-waters. 



In the present state of our knowledge, the foregoing facts 

 would appear to lead to the following conclusions : — 



(a) Quartz veins have been produced by the slow deposi- 

 tion from aqueous solutions of silica on the surfaces of the enclo- 

 sing fissures*. 



(b) From the general parallelism with its walls of the planes 

 of any fragments of the enclosing rock which may have be- 

 come imbedded in a vein, it is to be inferred that they were 

 mechanically removed by the growth of the several layers to 



* By " aqueous solution" it is not intended to convey the idea that 

 silica has been dissolved in pure water, but rather in waters containing 

 various acids, alkalies, salts, &c. 



