500 Professor T. G. Bonney — RocJcsfrom Kimherley. 



3. Sedimentary Bocks. 



" No. 7, Quartzite " : a large angular fragment with sub- 

 conchoidal fracture, of a darkish quartzite or hard grit, somewhat 

 felspathic, bearing a general resemblance to that described on the 

 last occasion.^ It seemed needless to have this sliced. 



" No. 9, north of dyke, 1,200-feet level." ^ A squarish block 

 (about 4" X 3" x 2") bounded by joint faces of a darkish-grey, 

 fine-grained felspathic sandstone. Under the microscope we see 

 snbangular to rather angular quartz grains, seemingly set in a matrix 

 of minute sericite-like flakes. This also suggests in places the 

 former existence of grains, which occasionally show the remains of 

 felspar. Some dark irregular spots (yellowish-white with reflected 

 light) prove with a magnification of about 80 diameters (which this 

 rock requires) to be aggregates of more or less translucent yellowish 

 to brownish granules, perhaps hydrocarbons. There are a few 

 small, rather rounded zircons, with other less important microliths. 

 The quartz grains appear to have been slightly enlarged. I have 

 no doubt the rock was once a quartz-felspar grit, but it has been 

 somewhat altered, perhaps by heated water. 



'•North-east side of dyke, 1,200-feet level": a large fragment, 

 smoothed on one side, of a fairly hard mudstone, in colour greenish- 

 grey, somewhat banded with darker layers (not sliced). 



" No. 4, Black Shale." This rock effervesces rather briskly with 

 HCl, and is a dark, compact or minutely granular, non-laminated, 

 calcareous mudstone, traversed by some very small veins of pyrite, 

 possibly with slight traces of gold. In the hope of finding remains 

 of organisms I had a slice prepared. The I'ock consists of roundish 

 or subangular granules of variable size, speckled brown, separated 

 by dark lines probably of carbonaceous matter. A few flakes of 

 a mica, probably a bleached biotite, are also present. I cannot 

 recognize any organisms, but one or two of the smaller grains exhibit 

 a ring-like structure, recalling the form of certain spores. The 

 grains generally show whitish to pinkish tints with crossed nicols, 

 and I think are very probably a dolomitic calcite, mixed with earthy 

 and carbonaceous matter. One or two small veins apparently are 

 filled with the first mineral. 



" No. 2, Limestone " : a compact cream-coloured limestone. As 

 the depth is not stated, I have not had it sliced, but I think it more 

 likely to have been formed by precipitation than by true sedimen- 

 tation, and to be from one of the tufaceous deposits said to occur 

 in the upper part of the diamantiferous breccia. 



" No. 6, Agate " : a mass of chalcedony and quartz which has 

 been formed in a cavity of a compact, rather decomposed basalt, 

 or possibly basic andesite. 



" Calcite " : from a vein of calcite with abundant pyrite and 

 possibly traces of copper, which apparently has traversed a darkish, 

 rather hard shale. 



1 Geological Magazine, 1895, p. 500. 



2 The 2 iu 1,200 is damaged, and may be a higher figure. 



