Professor T. G. Bonney — Roclcsfrom Kimherley. 499 



of crystalline grains ; (/) a few grains of calcite. The iron-oxide 

 and the supposed enstatite appear to have crystallized first. I expect 

 the crystallization of the augite and felspar was almost simultaneous. 

 The augite and the enstatite are often closely associated, and some- 

 times two long prisms of the former enclose one of the latter, like 

 a section of a sandwich. The rock may be called an enstatite 

 diabase. 



"Hard rock No. 18, 1,500-feet level": a dark basaltic rock, 

 slightly speckled with grey, and with occasional grains of felspai'. 

 The specimen is about 5|-" x 4" x 2". The minerals are practically 

 identical with those in the last rock, but the augite is more often 

 idiomorphic; rods of iron are more frequent, and these sometimes 

 form rude gratings. Thus it also is an enstatite diabase. In the 

 slice a small rock fragment, about one-eighth of an inch in diameter, 

 is enclosed. This at first sight seems to have a base of a speckled 

 pale-brown glass, but that, on applying the nicols, proves to be really 

 holocrystalline. In it are scattered some greenish-brown rods and 

 flakes, probably altered pyroxene or biotite, with a rosette of chlorite 

 and a few granules of iron-oxide. I suspect this to have been an 

 andesite, caught up by the more basic rock and altered by heat. 



" Shaft rock No. 19, 1,540-feet level." This is a dark-coloured 

 basalt, very minutely speckled with lighter-coloured felspar, and 

 containing a few grains of pyrite. The fragment is roughly five- 

 sided, about 3|- inches across, and 1 inch at thickest. The s.g. 

 is 3"033. Under the microscope the rock shows traces of a base 

 of a pale-brownish colour, but this proves to be replaced by secondary 

 microlithic products. In it the following minerals are thickly 

 scattered : (a) plagioclase : a few moderate-sized, broken crystals, 

 rather decomposed, are associated with grains of iron-oxide, and very 

 many long lath-like clear crystallites, often in pairs, parted by a very 

 thin wedge of the base ; these are not seldom associated in rather 

 divergent groups ; (h) brownish augite, imperfectly idiomorphic, 

 inclining to occur in clusters ; (c) iron-oxide, in crystalline grains, 

 granules, and rods, the second and third often associated to form 

 knotty clubs, combs with sloping teeth, or (rarely) gratings. 

 There are occasional grains of pyrite. The larger felspars certainly, 

 the augite not improbably, represent an earlier stage in the history 

 of the rock, which is a rather altered magma-basalt. 



" Soft rock, 1,500-feet level. No. 17." This obviously differs much, 

 from all the others. It is an irregular fragment, not quite four inches 

 long, of a rather light lilac-grey rock, mottled by dull-green spots, 

 varying in shape and size. The s.g. is 2-667. The rock consists 

 of a number of small lath-shaped felspars, with some rounded prisms 

 and spots of a very pale-green mineral, which acts but feebly on 

 polarized light, in a granular brownish-grey ground-mass, which 

 appears to be crowded with tiny lath-like microliths and minute 

 mineral specks. It breaks up, with crossed nicols, into irregular 

 spots, with low polarization tints, like a devitrification structure. 

 The above-named " dull-green spots " are fiUed-up cavities. The 

 rock is now a variety of porphyrite. 



