Dr. R. F. Band — Some Transvaal Eruptives. 109 



mosaic. Of tlie larger plagioclase fragments, some are bent, some 

 are broken. The microcline appears to be of tougher nature than 

 the plagioclase, having survived in larger fragments ; these show 

 a vague, undulatory extinction. 



Nos. 7, 8, and 9 present some resemblances among themselves 

 sufficient to w^arrant their being grouped together. 



No. 7. — Locality : near by the spur of the Witwatersrand Series, 

 around which the stream winds in its escape northwards out of the 

 Bezuidenhout Valley. From bed of stream. The rock occupies an 

 intermediate position between the granite and the eruptive which 

 occupies the floor of the Bezuidenhout Valley, a rock which is 

 referred to later on. 



Meg. A close-grained, holocrystalline rock, of dark bluish-grey 

 colour. Sp. gr. 2-96. 



Mic. The prevailing elements are rhombic pyroxene and amphi- 

 bole, the two often intergrown. The hornblende is very pale, and 

 appears to be largely derived from the bronzite, of whose crystals 

 it often constitutes the core. The bronzite is in large columns with 

 brush-like endings. Much of it has undergone the usual bastitic 

 alteration. Isolated crystals of hornblende occur, showing good 

 prismatic cleavages. Amidst the foregoing lies greatly decomposed 

 plagioclase with broad albite lamella3, and having epidote as its chief 

 decomposition-product. There is also a little quartz and a micro- 

 graphic intergrowth of quartz with felspar. Chlorite is present 

 in a few stray patches. Pyrites occurs in fair quantity. Opaque 

 patches of reddish tinge may be stained leucoxene, which is 

 apparently passing over into sphene. It may denote a pre-existent 

 ilmenite, and sometimes lies in association with the pyrites. 



No. 8. — Locality : irregular mass intrusive in the Witwatersrand 

 Series near Sans Souci. A few hundred yards distant from the 

 granite. 



Meg. A fine-grained rock, holocrystalline. Colour dark-bluish 

 black and light grey, in fine mottling. The weathered surface is 

 rusty. Sp. gr. 2-91. 



Mic. The most abundant constituent is hornblende, pale in 

 colour, sometimes twinned, oftentimes fibrous. It interlaces with 

 a greatly decomposed columnar plagioclase. In the meshes lies 

 a micrographic intergrowth of quartz and turbid felspar. A clear 

 plagioclase, referable to labradorite, is present in quite subordinate 

 quantity. Ilmenite is present, mostly decomposed into leucoxene, 

 and here and there are a few specks of pyrites. 



No. 9. — Locality : from a dyke traversing the granite in Bramley 

 township, 6 miles N.N.E. of Johannesburg. The dyke trends 

 north and south. 



Meg. Much resembles No. 8 in appearance, but is slightly darker 

 in colour. Sp. gr. 2*99. 



Mic. The appearance is ophitic. The meshes of the striped 

 felspar are occupied by serpentine, apparently derived from horn- 

 blende, of which some unaltered fragments remain. The hornblende 

 itself is probably largely secondary. The serpentine is frequently 



