Dr. R. F. Rand — Some Transvaal Eruptims. Ill 



Mic. Ground-mass microlitic as in No. 10. There is less of the 

 opaque matter and more amphibole in needles and wisp-like flakes. 

 Specks of magnetite are fairly plentiful. Many of the amygdular 

 cavities are entirely filled with a mosaic of quartz, which, in turn, 

 sometimes includes a little pyrites and sometimes epidote. Other 

 cavities are filled as in No. 10, and again others carry epidote 

 exclusively. 



Eruptive occupying the floor of the Bezuidenhoiit Valley. 



Nos. 12, 13, 14, 15, 16, and 17 as examples. 



This rock has a strong likeness to the Klipriversberg amygdaloid ; 

 it is separated from it, however, by a large section of the Witwaters- 

 rand beds, some 4 or 5 miles of their outcrop intervening between 

 them. The rock is schistose, in places, at the upper, narrower end of 

 the valley. Lower down and beyond the spur of the Witwatersrand 

 Series, which there terminates the northern flank of the valley, the 

 rock comes into relation with that described under No. 7, an inter- 

 vener between it and the granite. 



No. 12. — Locality : Bezuidenhout Valley township, north side of 

 stream, 2^ miles east and a few points north of Johannesburg. 



Meg. Closely resembles No. 10. The felspar crystals, however, 

 are small. Sp. gr. 2-87. 



Mic. Felspathio microlites are larger than in No. 10, some of 

 them forming small striped laths. Among them is much amphi- 

 bolic materia], in needles and wisps, and a good deal of the opaque 

 white material noted in No. 10. Epidote occurs plentifully through- 

 out the section in irregular grains. 



No. 13. — Locality : same as No. 12. 



Meg. A weathered specimen, amygdular. The contents of the 

 amygdular cavities have, in many instances, weathered out, so that 

 there is a partial reversion to the original cellular condition, a change 

 reflected in the low specific gravity, viz. 2*47. 



Mic. A microlitic ground-mass with occasional members of some- 

 what larger size. Interstitially there is much chlorite, pleochroic, 

 and nearly isotropic. Scattered abundantly throughout the section 

 are irregular patches of a dark-brown, semi-opaque material, white 

 by reflected light. I believe it to be leucoxene in course of 

 alteration into sphene, and perhaps rutile. Many of the amygdular 

 cavities are empty ; where filled, the peripheral portion consists of 

 completely isotropic serpentinous matter, sometimes iron-stained; 

 the central portion is made up of quartz-mosaic. 



No. 14. — Locality : from a point lower down the Bezuidenhout 

 Yalley, opposite the Geldenhuis tailings-heap. 



Meg. A close-grained, bluish-black ground, enclosing opaque- 

 white tabular crystals of felspar. One of these in the specimen 

 measures 2 cm. in length. Sp. gr. 2-87. 



Mic. The ground-mass consists of small plagioclase laths of more 

 ^cid type than the felspathic phenocrysts. These latter are greatly 

 decomposed. They are probably to be referred to oligoclase- 

 andesine. Among the laths lie dirty-green, platy forms with 



