52 Prof. T. Rupert Jones^Blamond Fields of S. Africa. 



together with some kinds of gneissic and igneous rocks (''amygda- 

 loidal wacke "), as occurring in a ridge parallel with, and distant a 

 few miles on the north from the lower Vaal (reaching as far as 

 Sitlacomie's village) in the same district. These are probably palaso- 

 zoic rocks, cropping up from beneath, to the north of the river. 

 Dr. Shaw says that " trap, metamorphic, and conglomerate rocks," 

 occur all through the Vaal Valley, and that frequently there is 

 '•'basalt protruding through conglomerate and amygdaloid trap;" 

 but these so-called '•' metamorphic " rocks are not clearly defined, 

 and the " binary granite," ^ " sj^enite," " clay-schists," and " sand- 

 stone," if not debris of rocks from the Transvaal, to the north and 

 north-east, may be remnants of the Karoo beds and of their igneous 

 dykes, intercalations, and included boulders ; whilst his " chalk or 

 something like it " is probably the well-known superficial tufa of 

 the district. 



Dr. Muskett has noticed that sandstone, passing upwards into 

 conglomerate, regularly stratified, traversed by trap-rocks, and 

 similar to that in most of the hills between Graaf-Eeinett and Port 

 Elizabeth, forms the base of the (Lower ?) Vaal Valley. This in- 

 dicates the continuance of the Karoo beds. 



Some extracts from the diary of Mr. G. S. Higson, published by 

 Professor Tennant (with some notes on diamonds, etc.) in 1870, give 

 the clearest account of the geology of the diamond-fields of the Vaal. 

 He left Bainsvlay, near Bloemfontein, in March, and next day on 

 the Modder, opposite Wonderkop, be saw blue and ochreous shales 

 of the Karoo series, " capped with the common blue basaltic trap 

 or ' ironstone ' of the country." In the Middelveld, at the end of the 

 next stage, he noticed that " one of the hills had a thick coat of 

 coarse sandstone under the trap, and overlying the clay-shales." 

 Passing several farms, he came to Bultfontein (or Du To it's Pan), 

 where many small diamonds had been found. Here in two water- 

 pits " good sections of the shale-formation are brought to view, in- 

 tersected and upraised by the basaltic dykes ; in one, to an angle of 

 about seven degrees, sloping off from each side of the dyke, and 

 striking east and west ; in the other the shales are tilted up to about 

 25°. This is contrary to the experience of the late eminent geolo- 

 gist, A. Gr. Bain, in similar Dicynodont formations in the Old Colony, 

 where effusions of trap have not disturbed the horizontality of the 

 shales. May not this have something to do with the local distribu- 

 tion of the diamonds ? " Having left Pniel, he came upon a section 

 " by the side of the road, going up the river, between the station 

 and Mr. Hay ward's farm," showing " where the clinkstone and 

 amygdaloid had run over the basaltic trap." At the diamond-dig- 

 gings below Pniel " the formations on both side of the river are 

 similar — basaltic, greenstone, and quartz dykes intersecting the 

 ground, and crossing through the river from side to side." Mr. 

 Higson then adds — " Went about the hills searching, but without 

 success. Examining a gully about 1^ miles down the river, I was 



1 A granilite, or binary granite, is alluded to by Mr. Higson (see further on, p. 53), 

 as being the fundamental rock of the Vaal Valley. 



