Becker — Auriferous Co7\ glomerate of the Transvaal. 203 



the products of decomposition of pyrite. Recrystallization is 

 a process which goes on in the presence of weak solvents. 

 Recrystallization of rock components is a very common thing, 

 and the ordinary phenomenon called metamorphism is substan- 

 tially recrystallization. The quartzite walls of the Main Reef 

 are in part recrystallized sandstones, and recrystallization of 

 silica has certainly taken place in the banket. Some recrystal- 

 lization of gold and pyrite in the blue may very probably have 

 occurred as an incident to general metamorphism or to the 

 formation of the white veins. Hence the impregnation theory 

 is not the only one which will account for the state of one 

 portion of the gold and pyrite, and the fact that it could 

 explain this state is insufficient to outweigh the many objec- 

 tions to the theory. 



On the whole, then, it appears to me that this theory is 

 untenable. It is popular with engineers accustomed to quartz 

 veins, partly because it involves a close analogy between the 

 Rand deposits and the more familiar type of gold deposit. 



The theory maintained by Mr. De Launay in his latest work 

 is that the sea in which the banket was deposited, was a satu- 

 rated solution of gold and pyrite. These minerals were pre- 

 cipitated as the banket accumulated, a part of the pyrite being 

 at the same time waterworn. This theory is an elaboration of 

 Mr. Penning's. It avoids some of the objections to the 

 impregnation hypothesis. The absence of rake veins and well- 

 marked chutes is consistent with the scheme of Messrs. 

 Penning and De Launay, and it would account fairly well for 

 the patchiness of the reefs. Mr. Penning was driven to it by 

 the angularity of the gold; Mr. De Launay, by the supposed 

 importance of the rarity of gold in the pebbles. 



The precipitation theory, however, is by no means free from 

 objections, chief of which is that it gives no account of the 

 most important feature of the deposits, namely, the association 

 of gold in largest quantity with the coarsest banket. One 

 would expect to find the sands at least as much mingled with 

 the auriferous precipitate as the banket. Precipitates are 

 usually thrown down in a fine state of division. How is it, 

 then, that the currents which swept away all mud and fine sand 

 did not also carry off the crystals of gold and pyrite before 

 they had time to reach considerable dimensions ? To meet this 

 evident objection Mr. De Launay makes the following state- 

 ment : 



Pour tenir corapte de ce fait characteristique que For est 

 presque-exelusivement dans les conglom6rats et won dans les gres 

 intermediates, on admettrait l'influence d'une preparation mecan- 

 ique ayant concentre l'or et la pyrite, en leur qualile d'elements 



