196 Becker — Auriferous Conglomerate of the Transvaal. 



mining the nature of the gold deposits. This is quite a mis- 

 take, as I shall explain somewhat later. I was assured that 

 free gold has repeatedly been observed in the pebbles with the 

 naked eye, but I did not succeed in getting a sight of any 

 such specimen. Mr. Pelikan, however, has found moss gold 

 embedded in the quartz of his specimens, and has photographed 

 under the microscope the occurrence of gold embedded in 

 quartz. These photographs are published in Mr. Goldmann's 

 work,* with different tints for pyrite and gold. I possess a 

 slide of Ferreira ore which shows free gold solidly embedded 

 in a quartz pebble. 



The matrix of the banket contains most of the gold and 

 pyrite. Some of the pyrite in the matrix is said to be in well- 

 defined, sharp crystals, but much more of it is in the form of 

 rolled pebbles. In some of the ores of the district it is evi- 

 dent to the naked eye that pyrite pebbles exist, but in most 

 cases a thin section is needed to display them. Dr. Koch says 

 that the grains of pyrite are generally shaped by attrition, or 

 at least display rounding of the edges and corners. This is 

 confirmed by Mr. Pelikan. Mr. De Launay also calls especial 

 attention to the fact that the pyrite often occurs in grains which 

 are rolled, or at least broken, blunted, or rounded. He finds 

 such pyrite pebbles extremely prevalent both in the Main Reef 

 series and elsewhere. He considers the pyrite pebbles as aurif- 

 erous, and mentions having observed under the microscope 

 gold embedded in the pyrite, without stating whether in these 

 particular instances the pyrite was rounded or not.f In some 

 of the specimens which I have examined the pyrite is sub- 

 stantially all in the form of well-rounded pebbles, issolated 

 from one another by sand and secondary minerals. No one 

 who has seen such specimens would admit for a moment either 

 that the pyrite was not rolled or that it was fractured by move- 

 ment in the rocks during upheaval. The pebbles have been 

 worn round, and the detritus has been removed. In several 

 cases they are externally converted into a brownish-black 

 mineral, which is probably hematite, and the conversion must 

 have taken place before the upheaval of the banket, for the 

 specimens are blue and fresh. The pyrite pebbles measure on 

 the average one-tenth of a millimeter in diameter. In some 

 specimens the pyrites are densely crowded into layers and the 

 pebbly character is less apparent. Some recrystallization may 

 have gone on in these cases, but I did not succeed in finding 

 the well-defined crystal outlines usual in embedded sulphurets. 

 The pyrite pebbles in many cases contain numerous scattered 



* South African Mines, by C. S. Goldman, 3 vols., 1895-96, vol. 3, plate 6. 

 f Les Mines d'or du Transvaal, 1896, pp. 306, 347. 



