318 Professor T. G. Bonuey — Parent-roch of the Diamond. 



includes numerous rounded fragments a little darker than the 

 matrix, with others, angular to sub-angular, some also darker and 

 some lighter than it. 



A brief summary of the results of microscopic examination may 

 suffice, as these rocks do not materiall}' differ from specimens 

 obtained in the De Beers Mine, of which I have published a full 

 account ^ 



The matrix is a mixture, in slightly variable quantities, of 

 granules of calcite or dolomite, serpentine, pyroxene, and iron 

 oxides, in which occur flakes with fairly idiomorphic outlines of 

 a warm-V)ro\vn mica, moderately pleochroic, corresponding with that 

 <lescribed'^ in one or two specimens from De Beers Mine. The 

 prisms are about 0'002 in. in diameter, and sometimes nearly as 

 thick. This mica, which, as stated in a former paper, I consider 

 a, secondary product, occurs abundantly in all the specimens, but 

 in that from the interior (on the whole the best preserved rock) it 

 is locally assuming a green colour, no doubt by hydration. In the 

 specimens from the thick rib, the one last named contains mineral 

 grains and rock fragments, except for a few flakes of the usual mica. 

 The former are a mixture of two fibrous minerals, the larger part 

 •corresponding with actinolite ; the rest, giving lower polarisation 

 tints, may be serpentine. This fact, and structures suggestive of 

 the former presence of a cleavage more regular than that of olivine, 

 make it more probable that d topside was the original mineral. 

 Though iron oxide is present in specks and rods (especially in the 

 worse preserved specimen), this occurs either in the outer part, or 

 as though it had been deposited along cleavage planes. In the thin 

 rib of 'blue' (iii), some of the grains are composed partly of 

 a fibrous mineral, as above described, and partly of a clear one, 

 which often affords i-ather rich polarisation tints, and presents some 

 resemblance to quartz. Its precise nature is difficult to determine, 

 owing to the absence of distinctive characters, but I believe it to 

 be of secondary origin. Rock fragments are not common in the 

 first (interior) specimen (vii) ; one, however, is probably an altered 

 shale, and another possibly a limestone. This is bordered by a pale, 

 pyroxenic mineral piercing into the grains of calcite. In the 

 second specimen (vi) fraguients are rather common ; among them 

 are those of diabase, ranging from fine to coarse, one specimen of 

 the latter, originally, perhaps, an inch in diameter, slaowing an 

 ophitic structure ; felspar and augite both being rather altered, 

 seemingly by infiltration, and one small fragment resembles a sub- 

 crystalline limestone. Specimen (v) does not materially differ, but 

 seems to contain more carbonate than the others. The dark 

 streaking is due to grains of iron oxide or serpentine with much 

 opacite ; rock fragments few and small. Specimen (iii) from the 

 thin vein contains a few very small rock fragments, mudstone or 

 shale, more or less altered, possibly also a compact diabase. The 

 ■* country rock ' is a mudstone, consisting of small chips of quartz 



1 Geol. Mag., 1895, p. 492 ; and 1897, p. 448. 



2 Geol. Mag., 1897, pp. 450, 451. 



