110 Dr. R. F. Rand — Some Transvaal Eruptives. 



bordered with a bem of chlorite, with pleochroism green to blue. 

 Quartz is present in fair quantity. Plates of ilraenite are abundant, 

 decomposed for the most part into leucoxene. A few crystals of 

 apatite occur. 



Klipriversherg Amygdaloid. 



Nos. 10 and 11 illustrate this rock, which overlies the Witwaters- 

 rand Series some 5 miles south of Johannesburg, where it forms 

 a range of rugged hills. In places it shows a characteristically 

 amygdaloidal structure, which is brought out very clearly by 

 weathering, the resistant quartz amygdules standing out in bold relief. 



No. 10. — Locality : northern fringe of Klipriversherg Kange by 

 Meyer's Farm, 5 miles south of Johannesburg. 



Meg. A dark bluish-grey rock of dull, fine-grained texture, the 

 ground carrying a few glassy, tabular crystals of felspars showing 

 albite striation. Darker spots represent the amygdules, which, in 

 the specimen under review, are small. Sp. gr. 2 83. 



Mic. The ground-mass is made up of a mass of felspathic 

 microlites, mostly showing the parallelism indicative of flow. 

 Amidst the microlites is a good deal of granular opaque matter, 

 which is white by reflected light. The microlites are long and 

 slender, and, as they extinguish almost parallel with their length, 

 are probably oligoclase. Some of larger growth are striped. Lying 

 among the felspathic microlites of the ground-mass are numerous 

 fine needles of amphibole, which appear to grow at the expense 

 of the opaque matter noted above, increasing in number as the 

 opacity clears up. 



The large felspar phenocrysts are few in number, are much 

 decomposed, and show albite twinning. The ferro-magnesian element 

 of the first generation is represented by pseudomorphs of pale- 

 greenish chloritic matter, granular in appearance, faintly pleochroic, 

 and ranging between crossed nicols from an intensely deep blue 

 to complete isotropism. These pseudomorphs perhaps succeed 

 olivine. They frequently enclose epidote in good crystals. 



The amygdular cavities show varying contents. They are 

 commonly filled in part by a material very similar to that of the 

 pseudomorphs. but which in the amygdular cavities passes over 

 into, what is doubtless to be regarded as, isotropic serpentine. This 

 material borders the wall of the cavity, encroaching deeply upon 

 its area ; centrally, the core of the amygdule is formed by a mosaic 

 of quartz. Epidote is frequently seen in the chloritic matter, and 

 its advancing growth is indicated by a faint shadow margining 

 its edges; this is pleochroic, and recalls the pleochroic halos common 

 in the biotites, but lacks their intensity. Eutile is an occasional 

 inclusion in the amygdular chlorite. One cavity is almost completely 

 filled with augite, decayed centrally, where it is studded with grains 

 of quartz and magnetite crystals. 



No. 11. — Locality : southern edge of Klipriversherg Range, about 

 8 miles south of Johannesburg. 



Meg. Eesembles No. 10, but the amygdular cavities are larger 

 and are filled with white quartz. Sp. gr. 2 '93. 



