500 Pro/. Bonney and Miss Raisin — Rod's from Kimherley. 



(c) Fragments of olivine, of a greenish-yellow colour, not very 

 numerous. 



{d) Iron oxides. Grains of magnetite are very few in number — 

 Bot one per cent, of the washing ; most of the grains are not attracted 

 by the magnet, have a bright metallic lustre, give a brownish streak, 

 and a bead (with borax) of yellowish bottle-green colour. These are 

 clearly ilmenite, as was further indicated by the usual chemical test. 

 We have not found chromite, but, as our search has not been a very 

 close one, it may have escaped us. It can hardly be common. A 

 good many subrotund grains or little flattish cakes of rusty brown 

 colour prove to be limonite. 



(e) Occasional grains of pyrite and quartz, and flakes of brownish 

 mica. 



Two other rock specimens, brought back by Sir J. B. Stone, must 

 also be noticed. One is a somewhat shapeless lump, with rather 

 rounded surfaces, more or less slicken-sided, unctuous to the touch, 

 and of a pale olive-grey colour. The hardness of the exterior is 

 about 1'5, but a portion of the interior exposed by a fracture is a 

 little less than 3. The former, when powdered, does not effervesce 

 with HCI, and under the microscope resembles a rather decomposed 

 serpentine ; the latter effervesces briskly, and appears to be mainly 

 calcite, perhaps slightly dolomitic. We seem, then, to have a nodule 

 of impure calcite, of what origin it is difficult to say, enclosed in 

 a kind of husk of decomposed serpentinous material. 



The other specimen is a hard, fine-grained grit or quartzite, 

 almost black in colour, with a thin banded structure, parallel with 

 which it has a tendency to split, especially where a white mica 

 (fragmental) is abundant. A microscopic section shows it to con- 

 sist mainly of fragments of quartz, fairly angular to subrotund, a few 

 being compound and possibly derived from veins. The majority 

 contain fluid cavities, although the amount of these is variable ; 

 bubbles, frequently small, are generally present, and microlithic 

 enclosures may be occasionally noted. Often there is a thin 

 external zone of secondary quartz. A few fragments of felspar, 

 including a plagioclase, and microcline also occur. The grains are 

 set in an earthy matrix, a good deal of which on close scrutiny has a 

 fragmental aspect, and very probably is largely made up of decom- 

 ])Osed felspar. This part, with crossed nicols, is brightly speckled, 

 most likely owing to the formation of a secondary micaceous 

 product. We find also ilmenite, partly converted into leucoxene, 

 a few flakes of altered biotite, and sundry microliths. On one side of 

 the slice are one or two bands of variable thickness, where the rock 

 is darker and more fissile, the fragments being smaller, and the 

 amount of mica (chiefly white) being larger ; here also are some 

 grains of pyrite. Pi'obably the rock is a member of the Karoo 

 series, though possibly slightly altered. 



Our observations accordingly seem to justify the following state- 

 ments : — 



(1) That the diamantiferous rock is a breccia, which in its 

 unweathered condition is cemented together by secondary minerals. 



