204 Becker — Auriferous Conglomerate of the Transvaal. 



lourds, avec les galets les plus gros, comme cela s'est passe pour 

 tous les depots d'alluvions auriferes. 



Thus this geologist supposes a relatively quiet deposition of 

 gold and pyrite from sea water in unsorted material, followed 

 by a natural concentration. Now, sorting begins the moment 

 that detritus from the land reaches the sea. I perceive no 

 opportunity for the supposed quiet precipitation of gold and 

 pyrite; nor do I understand why precipitation, if it takes place 

 at all, does not continue during the sorting process, so that the 

 sands eliminated from the pebbly material would continue to 

 be enriched by precipitation. 



The fundamental hypothesis of a sea highly charged with 

 gold and pyrite seems to me extremely improbable. Had the 

 ocean at any time been so charged, the mineral would, as Mr. 

 De Launay says, be precipitated with extreme ease. How then 

 could the ocean become highly charged? It would seem that 

 the gold and pyrite going into solution, say at the mouth of 

 some submarine solfataric vent, must be thrown down almost 

 immediately and close to the point at which solution took place. 

 An almost uniform distribution of gold along a coast known to 

 be at least 30 miles in length would then be impossible. 

 Again, if the ocean ever was so powerful a solvent for gold, 

 why are there not many and indubitable cases of deposits 

 formed by this method ? 



The advantages of the precipitation theory over the simple 

 detrital theory are, as 1 understand Mr. DeLaunay, that the 

 former hypothesis explains why there is no gold or pyrite in 

 the pebbles and why the gold is not substantially all on the 

 foot wall of the reefs. These advantages are by no means 

 substantial ones, as will presently appear. 



As has been noted above, pebbles which carry crystallized 

 pyrite and other sulphurets disseminated through the quartz, 

 and not on fissures of any sort, are fairly abundant on the 

 Rand. Gold is also known in the pebbles. Some writers con- 

 sider it very strange that if the pebbles came from auriferous 

 quartz veins, gold-bearing pebbles are not more abundant* As 

 a matter of fact, in the auriferous river gravels of California 

 and Venezuela, pebbles showing visible gold are extremely rare. 

 Even in the vast exposures of the hydraulic washings one 

 might spend weeks in the vain search for a specimen. In the 

 sluices, however, small pieces of auriferous quartz may be 

 found with the gold, separated by the concentration process 

 from thousands of tons of barren pebble. On the auriferous 

 beaches of California, Oregon, aud Alaska, such pebbles seem 



* Mr. Curtis did not adduce the rarity of gold-bearing pebbles in favor of the 

 impregnation theory, no doubt because of his familiarity with California gravels. 



