Becker — Auriferous Conglomerate of the Transvaal. 197 



particles of gold, which may be seen by very strong incident 

 light. I have observed this both in my own slides and in Mr. 

 Johns's suite. 



The free gold in the matrix, like the pyrite, seems to be in two 

 different conditions. Dr. Koch found the metal in minute crys- 

 tals, or in irregular sharp-cornered, hackly aggregates. Mr. Peli- 

 kan observed it in irregular lumps, grains, and scales, which, in 

 his opinion, correspond beyond a question to alluvial occur- 

 rences. According to Mr. De Launay, the gold almost always 

 occurs as extremely minute scales, often so thin as to be translu- 

 cent, very rare exceptions being aggregates of gold on the white 

 quartz veins, small masses of free gold crystallized by secondary 

 solution in the banket, and coatings on joint planes. Mr. Crosse 

 also has found evidence of the existence of gold in a crystalline 

 condition. In my slides the gold in the matrix corresponds 

 most closely to Mr. De Launay's description. It appears in 

 irregular flakes and scales, which often conform to the accom- 

 panying sand grains, as if pressure had molded the metal. The 

 grains are not smooth, but neither have they either the crys- 

 talline appearance or the hackly surface of gold in vein quartz. 

 The scales are often excessively thin, and pass over into mere 

 yellowish-brown stains in which, by the help of direct sunlight, 

 shining yellow points can be observed. The smaller scales of 

 gold found on beaches are not ordinarily smooth, but they are 

 smoother than those of the banket. I believe that pressure 

 and the roughness of the surrounding detritus have determined 

 their outlines to a large extent in the puddingstone. 



Besides the more important minerals of the banket, Dr. 

 Koch found in the matrix magnetite (also noted by Mr. Curtis), 

 zircon, rutile, tourmaline, muscovite, chlorite, and a colorless 

 highly refracting mineral not determined. Mr. Pelikan found 

 biotite and a greenish mineral, perhaps identical with Dr. 

 Koch's, which he suspects of being pyroxenic. Dr. Hatch 

 notes marcasite, copper pyrites, blende, galena, ilmenite, and 

 magnetite ; he also records that Mr. Crosse has detected corun- 

 dum by chemical means. 1 have repeatedly found pyrrhotite 

 in the mines (for example, in the Crown Deep), but only in 

 association with the white quartz veins referred to above. 

 There is either magnetite or hematite among the pebbles of 

 my slides, and zircons were observed, The main mass of the 

 matrix consists, besides gold and pyrite, of sand grains, chlorite 

 and sericite, and secondary quartz. It is interesting and 

 important to compare this matrix with slides of the quartzite 

 adjoining the banket, because many grains which might be 

 interpreted as secondary in the matrix are there seen to be 

 mere sand. In both quartzite and matrix it is apparent that 



