374 E. H. L. Schwarz — Gold in Cape Colomj. 



of water through tlie substance of rocks is sufficiently recognised, 

 and I think I need not labour the point that, if there are strata in 

 compression and a series of opening cracks within reasonable distance, 

 the water will pass from the one to the other. 



With regard to the power of water to dissolve metallic substances, 

 Doelter ^ found that pyrites, galena, antiraonite, spherulite, arsenical 

 pyrites, copper pyrites, and bournonite were to a certain extent 

 soluble in pure water when heated for four weeks in glass tubes to 

 a temperature of 80° C.,^ and that pyrites, galena, zincblende, arsenical 

 and copper pyrites, and bournonite were soluble in water containing 

 sodium sulphide under the same conditions.- There is, therefore, 

 no reason to suppose that enormous pressure or heat were necessary 

 to make these minerals go into solution, and that they must have 

 consequently come up from great depths ; with the exception 

 of blende the minerals ai'e soluble in pure water, given moderate 

 pressures and temperatures, such as would exist a few thousand feet 

 below the surface, for it must be remembered that in dealing with 

 these matters, where temperature and pressure are high in the 

 laboratory experiments, the same results can be attained in nature 

 by very much less temperatures and pressures, owing to the vast 

 lengths of time in which the process has to act. In the case of zinc- 

 blende an alkaline sulphide was found necessary to cause it to go 

 into solution, and whether the particular sulphide, or, indeed, salt of 

 whatever kind, was really present in nature, or some other, the main 

 point proved in Doelter's experiment was that the zincblende could 

 be made to go into solution. 



With gold we have a much more refractory element, but a trace of 

 free chlorine in the water would be sufficient to dissolve the gold 

 from the banket. The surface-water of Millwood is tinged brown 

 with organic acids derived from the roots of the grasses and sedge- 

 like plants that cover the slopes of the hills ; hydrochloric acid is 

 present in minute quantities, and may be accompanied with free 

 chlorine, so that the possibility of this solvent being present in the 

 underground water is not entirely ruled out. Other solvents are 

 sodium and potassium chloride,^ sodium silicate,* sodium sulphide, 

 sodium sulphydrate, and sodium carbonate saturated with sulpliydric 

 acid.® Le Conte and Wurtz have shown that ferric sulphate is also 

 a solvent, and Atkin ^ has pointed out that this is by far the most 

 likely of natural salts that cause the solution of gold. 



Posepuy has argued that water circulating within a few hundred 

 feet of the surface, and derived by absorption from the atmospheric 

 water, would be an agent which oxidized the salts which it carried 

 in solution, and therefore, if we accept his theory, the sulphides 

 which colour the sandstones blue, would first yield a sulphate, and 



1 Tschermak's Mitth., 1889, vol. xi, p. 319. 



2 I.e., p. 323. 



^ Edeston: Trans. Amer. Inst. Min. Ena:., 1880, vol. viii, p. 455. 

 ^ Liveisidge: Proc. Roy. Soc. N.S. Wales, 1893, vol. xxvii, p. 303. 

 5 Becker: Mon. U.S. Geol. Surv., 1888, vol. xiii, p. 433. 

 « Atkiu: Q.J.G.S., 1904, vol. Ix, p. 390. 



