452 Professor T. G. Bonney — Rochsfrom Kimherley. 



with small prisms which give low polarization tints and oblique 

 extinction. These towards the outer pai't are more thinly scattered, 

 are about five times as long as wide and a little ragged at the ends, 

 and are pale greenish or brownish with rather bright polarization 

 tints and extinction angles high enough for augite. The almost 

 colourless base, in which these and some yet smaller microliths are 

 scattered, seems generally to be isotropic, but here and there small 

 aggregates occur of some feebly double-refracting mineral. The 

 interior of another fragment in (a) is more varied : it contains several 

 ragged flakes of a brown mica, somewhat bigger than the prisms. 

 Also minute grains of a clear mineral, with a high refraction index. 

 Their form suggests an isometric mineral, but they afford bright 

 tints with crossed nicols. Thirdly, a fair number of roundish 

 grains of larger size, colourless, but giving faint indications of 

 a flaky structure, with no visible effect on polarized light. The 

 exterior of a fragment in (6) shows a considerable amount of 

 a very pale-brown mica, and prisms or flakes of a colourless mineral, 

 extinguishing as hornblende rather than augite. The interior is 

 granular in structure, ferrite-stained, with numerous black specks 

 variable in size and some flakelets of brown mica.^ It has 

 a fragmental aspect, and may contain some bits of decomposed 

 felspar. In another fragment the narrow outer part is blackened 

 with opacite, though a clear ground-mass, like serpentine, may be 

 distinguished, but the interior is much stained with ferrite. High 

 magnification, however, reveals a fair amount of brown mica and 

 a few black spots (? graphite). The small rock fragments in all 

 the specimens show a general correspondence with the outer zone 

 only of the larger, consisting of flakes or prisms of mica, pyroxene, 

 etc., in a clear ground-mass, resembling a serpentine, but possibly 

 a pseudophite. A subrotund fragment in (11) — the 1200-feet level, 

 East — about 1" in longer diameter, having the usual purplish- 

 brown interior and a banded greenish-grey outer zone, which is 

 quite y wide, has also been examined. The structure does not 

 essentially differ from some of those described above, except that 

 there is practically no suggestion of contact metamorphism. The 

 interior resembles a mudstone, probably rather carbonaceous, and 

 containing a few flakelets of a colourless mica. The outer zone does 

 not materially differ from the interior, except that it has a rather 

 more clotted aspect, and shows brown lines roughly concentric with 

 the exterior, probably indicating old cracks. In this zone an 

 infiltration of a colourless serpentinous mineral is perceptible, which 

 also occasionally (together with some streaks of a chloritic mineral) 

 fills an interval between the matrix and the fragments, and occupies 

 one or two cracks in the interior. 



These specimens of the diamantiferous breccia have afforded me 

 better opportunities of studying included fragments of sedimentary 

 rock than those described in 1895. I believe them to represent 

 ordinary shales or argillites, which have undergone two forms of 

 alteration. The first, not sufScient to change materially the general 

 1 Minute perofskite may be present in this fragment. 



