Becker — Auriferous Conglomerate of the Transvaal. 195 



exceed a few thousand pounds in value. With this exception 

 all of the gold of the Witwatersrand occurs in the banket 

 reefs, of which by no means all carry gold in remunerative 

 quantities. 



The banket is a highly siliceous mass, consisting of quartz 

 pebbles embedded in a matrix composed of sand, pyrite, and 

 other minerals, all cemented by secondary silica. The cement 

 has the same character as in ordinary quartzite. The large 

 quartz pebbles have all the characteristics of vein quartz, but 

 show under the microscope undulous extinctions and other evi- 

 dences of the dynamic action to which they have been sub- 

 jected. They are frequently cracked, and then sometimes 

 show veinlets along the fractures. The quartz pebbles often 

 carry pyrite and other sulphurets, as zinc blende and galena. 

 This was recognized by Dr. A. Koch,* who states that pyrite 

 occurs as inclusions in the quartz pebbles of almost all the con- 

 glomerates. So, too, Mr. A. Pelikanf states that in the suite 

 of specimens which he has examined pyrite is found as inclu- 

 sions in the quartz pebbles. Mr. De Launay denies this occur- 

 rence. Gold and pyrite, he says, exist exclusively in the 

 cement, never in the pebbles. In the Crown Reef mine I 

 found more than a dozen instances of the inclusion of sul- 

 phurets in the course of a brief search, and I observed a great 

 number of such cases in other mines on subsequent occasions. 

 These were cases in which the sulphurets were disseminated 

 through the quartz of the pebbles, not arranged on surfaces 

 which might be interpreted as recemented cracks. Under the 

 microscope I find many cases of the inclusion of disseminated 

 pyrite in pebbles of what is plainly vein quartz. Some of the 

 sulphuret-bearing pebbles are auriferous. One such which I 

 collected in the Crown Reef was large enough to bear trim- 

 ming, so that the outer surface could be entirely removed. 

 The residual kernel was assayed by Mr. A. F. Crosse and found 

 to contain gold in appreciable quantities. Prof. Le Neve 

 Foster;); states that assays by Mr. Richard Smith show some of 

 the pebbles to be auriferous. The question whether free gold 

 exists in the pebbles has been much discussed, and has been 

 treated as if it were a matter of the first importance in deter- 



* Vorkommen und Gewinnung der nutz. Min. in der Siidafr. Republik, by Carl 

 Schmeisser, 1895, p. 48. 



f Verhandl. k. k. geol. Reichsanstalt, 1894, p. 421. Dr. Koch examined banket 

 from the Simmer and Jack, Robinson, Village Main Reef, Meyer- and Charlton, 

 and Langlaagte Estate. Mr. Pelikan's specimens came from the Robinson, 

 Crown Reef, and Meyer and Charlton. I have slides from the Ferreira, Village 

 Main Reef, Crown Reef, Simmer and Jack, Robinson, City and Suburban, and the 

 Crown Deep. I have also examined a series from the Ferreira owned by the 

 general manager, Mr. Harry Johns. 



\ Text Book of Mining, 1894, p. 42. 



