Becker — Auriferous Conglomerate of the Transvaal. 207 



It has been argued that if the deposits of the Witwatersrand 

 are ancient beaches they are substantially unique. It is cer- 

 tainly true that they are the richest of such deposits ever 

 known, but geologically and qualitatively they by no means 

 stand alone. Europe. America, Australia, and New Zealand all 

 possess auriferous, marine gravels of pre-Tertiary age. Ancient 

 river gravels would be preserved only under exceptional cir- 

 cumstances, and it is doubtful whether a single case of pre- 

 Tertiary gold-bearing river gravels is yet known. It is inter- 

 esting to compare other old gold placers with the deposits 

 of the Witwatersrand, and for that reason notes on some of 

 them were added to my other paper. They certainly reenforce 

 the argument for the alluvial origin of the gold in the banket, 

 and it may be noted that nearly all of these deposits lie in the 

 regions known to contain gold-quartz veins older than the 

 marine strata. 



Let it be assumed for the sake of argument that the banket 

 really represents a marine placer of early Paleozoic age, formed 

 off the shore of an extensive gold-bearing region, and since in- 

 jected with dikes. One would then expect to find the gold in 

 the coarser streaks of the resulting conglomerate and on the 

 lower side of such streaks. The reef would extend for many 

 miles and perhaps for many hundreds of miles. The 

 tenor would depend in part on the strength of the cur- 

 rents sweeping along the coast, and in part on the quality 

 of the material fed into the sea at the different points, or at 

 the same point during different seasons. Hence, conglom- 

 erate of a given coarseness would be richer at some points 

 than at others, and there might be almost barren portions 

 or beds, but the distribution would be in patches, not in 

 chutes. The gold would almost all be finely divided, for nug- 

 gets would commonly remain in the rivers. Pyrite would 

 almost certainly appear in the sands, but experience shows that 

 gold-bearing pebbles would be rare. When the conglomerate 

 was upheaved, injected with dikes, and metamorphosed, it 

 would be found that the dikes sometimes cut poor patches and 

 sometimes rich ones, their disposition having nothing to do 

 with the original distribution of the gold. The sandstones 

 would be converted into quartzites, and recrystallization of gold 

 and pyrite would occur to some extent. In short, it seems to 

 me that deposits exactly analagous to those of the Rand must 

 form in this way, while in some details the composition of the 

 banket would doubtless depend on the lithological character 

 of the back country. 



Thus, it seems to me that there are no valid objections to 

 the theory of marine placer origin and no noteworthy features 

 left unexplained by this theory, while so much can not be said 



