Vol. 50.] CERTAIN NOVACTTLITES AND QT/ARTZITES. 389 



of certain bluish-grey, auriferous qaartzites, which he recognized as 

 similar to those occurring at Nondweni. 



A section cut from a small but rich fragment shows, when examined 

 tinder the microscope, that the rock is a quartzite, but that, in 

 addition to gold, it also contains a very considerable amount of 

 calcite. The quartz appears in polarized light as a mosaic of crystals 

 and irregular grains, which give positive uniaxial figures in con- 

 vergent light. The calcite occurs in irregular patches, strings, and 

 finely-shredded particles. The patches sometimes show very distinct 

 rhombohedral cleavage. Frequently small crystals of quartz occur 

 within, or irregularly mixed with, the calcite, and occasionally the 

 latter mineral appears as if squeezed between the crystals of quartz 

 (fig. 1, p. 388). 



Careful examination of the section leads to the conclusion that the 

 calcite does not form true veins in the quartzite, since the sharp 

 boundaries which almost invariably characterize veins are not present. 

 The calcite appears shattered, frayed, or shredded out where it comes 

 into contact with the quartz, suggesting the disintegration of the 

 former by a solvent (fig. 2). It might be urged that both the calcite 

 and the quartz crystallized simultaneously, but I can see no proof of 

 this, appearances pointing rather to the disintegration of pre-existing 

 calcite and infiltration of silica, which crystallized out as quartz. 



Fig. 2. — Auriferous quartzite from Nondweni, Zululand. 

 (Ordinary light.) 



x 140. 

 q = quartz, c = calcite. 



The gold occurs in irregularly-shaped particles, sometimes appa- 

 rently in octahedral crystals, and it is mainly situated in the calcite. 

 In some cases, however, it lies partly in calcite and partly in quartz, 

 while, to a small extent, it is disseminated in the quartzose portions 

 of the section. 



It would appear, then, that the gold originally occurred in a bed 



