Becker — Auriferous Conglomerate of the Transvaal. 205 



to be still rarer than in the river gravels. Thus the rarity of 

 gold-bearing pebbles on the Rand is such as should be expected 

 from analogy if the deposits belong to the class of placers. 



The presence of crystallized gold and pyrite is bj no means 

 unaccountable on the same theory. Even in the Tertiary 

 gravels of California recrystallization of sulphurets is now in 

 progress, and it is probable that recrystallization of gold also 

 has taken place to some extent. On the Rand it is certain that 

 solutions capable of dissolving gold to some extent have been 

 present below water level at some time since the original depo- 

 sition. These accompanied the formation of the white quartz 

 veins which cut the banket beds and which occasionally carry 

 a little gold. The same solutions must have been capable of 

 dissolving pyrite. The solvent fluids were probably hot waters 

 containing sulphides of the alkalies and carbonates. Such 

 waters dissolve gold and sulphurets, and they almost invariably 

 accompany eruptive activity such as is manifested in the dikes 

 of the Rand. Now, recrystallization being due to the action 

 of fluids which exercise a feeble solvent power, it would be 

 extremely remarkable (taking the existence of the white veins 

 into consideration) if the gold and pyrite of the banket showed 

 no evidences of recrystallization. It is quite as easy to account 

 for recrystallization of the gold and the pyrite as for the con- 

 version of the sandstone into quartzite. 



The objection to the theory under consideration, that the 

 gold is not uniformly found on the foot wall of the reef, is 

 entirely without weight. In auriferous river gravels, indeed, 

 most of the gold is found either on bed rock or on layers of 

 pipeclay ; but the banket is not a river deposit. As has been 

 explained already, river gravels are distinguishable both by r the 

 form of the pebbles and by their imbrication or "shingling" 

 from marine gravels, to which class those of the Rand belong. 

 The deposits are therefore comparable with the auriferous 

 beach deposits of the Pacific Coast or of New Zealand, and not 

 with the river gravels of the Sierra Nevada. In the beach 

 gravels the gold is found at the bottom of the layer of material 

 set in motion by the last wave or current by which the mass 

 has been agitated. Hence the beach deposits consist of strati- 

 fied masses of gravel and sand in which the gold is for the 

 most part confined to those layers which are composed of heavy 

 particles, but not necessarily to the bottom of such layers, for 

 if these have any considerable thickness, the upper part may 

 be disturbed without movement in the lower portion. Thus 

 thin layers of rich gravel, underlain and overlain by substan- 

 tially barren layers, are very characteristic of gold-bearing 

 beach deposits. 



On the Pacific Coast the gold is commonly associated with 



