112 Dr. R. F. Rand — 8ome Transvaal Eruptives. 



brush-like endings. These are probably hornblendic. There is 

 much epidote, in large irregular grains, sometimes interstitial, 

 sometimes enclosed in patches of chlorite. The amygdular cavities 

 are filled as in previous examples. Some of their chloritic matter 

 encloses biotite, which is apparently growing at its expense. This 

 specimen shows an approach towards the ophitic structure of the 

 diabases. 



Nos. 16 and 17. — Locality: Bezuidenhout Valley township, 

 3 miles east of Johannesburg. Both of these examples are schistose, 

 probably as a result of dynamic metamorphism. The vicinity 

 manifests, as has been pointed out by Drs. Hatch, Corstorphine, and 

 others, a high degree of faulting. 



No. 16. Sp. gr. 2-71. 



Mic. Individual detail is gone, and the body of the rock is now 

 made up of an exceedingly fine-grained crystalline basis, probably 

 the ground-down fragments of the felspathic microlites and crystals. 

 This ground-mass is traversed by strings of yellowish-green chloritic 

 matter and streaks of iron-staining. These course in rude parallelism, 

 approaching and diverging to leave lenticular interspaces. Large 

 irregular plates, of what is probably titaniferous iron decomposed 

 into a red-stained leucoxene, occur freely, and around these patches 

 the strings frequently wind. 



No. 17. — Meg. The schistose character is evident in the hand- 

 specimen. Sp. gr. 2-58. 



Mic. The general features resemble No. 16. The amygdular 

 cavities are much flattened out. The grains of their quartz-mosaic 

 have sometimes assumed a degree of parallelism, the direction of 

 arrangement being obliquely across the cavity and not in line with 

 its long axis. 



Note. — From the foregoing it will be seen that the Klipriversberg 

 amygdaloid and the Bezuidenhout Valley eruptive are much akin. 



No. 18. — Locality : an intrusive in the Witwatersrand Series ; 

 exposed in Witpoortje Kloof, some 12 miles west of Johannesburg. 



Meg. A dark bluish-black rock, holocrystalline, faintly mottled, 

 and of medium grain. Specks of pyrites are conspicuous. 

 Sp. gr. 2-92. 



Mic. The rock has the structure of the diabases, large felspathic 

 laths constituting a framework amid which the ferro-magnesian 

 elements are disposed. The felspar is greatly decomposed, but the 

 albite striping is to be made out. The ferro-magnesian constituents 

 are augite and olivine, intermixed in crystalline clusters. Both are 

 faint yellowish-brown in colour. Augite predominates. Both the 

 augite and the olivine are in course of alteration into serpentine, 

 and in both the alteration comes as an opaque cloudiness advancing 

 from the surface inwards. Detached pieces of serpentine and of 

 chloritic matter lie about in the section, the latter enclosing grains 

 of epidote. Large crystalline plates of magnetite are frequent. 

 More rarely, beautiful patches of pyrites occur, arranged in the 

 filigree-like forms it so often assumes. 



No. 19. — Locality : surface-exposure 2 miles east of Boksburg. 

 Possibly of Karoo age. 



