54 Prof. T. Rupert Jones — Diamond Fields of S, Africa. 



the flanks of the Zuurberg (near Grahamstown), this great trap- 

 breccia had received its felspathic character from metauiorphic in- 

 fluences (Quart. Journ. Geol. Soc, vol. xv., p. 198)« 



The Karoo "beds have been enormously denuded in the great 

 catchment area of the Orange and the Vaal, on a scale proportionate 

 to the vast destruction these strata have been subjected to through- 

 out their extent, as indicated by Bain^ and Eubidge,^ and more 

 elaborately described, in the case of the Eastern Province, by Mr. 

 Stow.3 



To the north-east of Cronstadt, the Vaal Valley comes into the 

 sandstone district (continuous with, and a part of, the Karoo series), 

 from off the old quartzites and gneiss of the Transvaal. These are 

 broken through by volcanic rocks (with craters to the south-west of 

 the Gats Eand, Transvaal), and associated with marble, and dyked 

 with granite, on that watershed of some of the northern tributaries 

 of the Vaal (Higson). The great Draakenberg or Quathlamba range 

 supplies the other head waters of this diamond-sanded river. The 

 Draakenberg consists of Karoo beds, intercalated and surmounted 

 with trap-rocks (Sutherland and Griesbach). 



The Wittebergen, also composed of Karoo strata and volcanic 

 rocks, branch off westward from this great range, at about 29° S. 

 Lat., and divide the head waters of the northern tributaries of the 

 Vaal from those of the Caledon and Orange Rivers, which, rising in 

 the Mont-aux- Sources or Bouta Bouta (about 10,000 feet above the 

 sea), at the divergence of these mountains, run over the Karoo 

 strata of Basutu Land, Smithfield, Colesberg, etc., to the neighbour- 

 hood of Hopetown, where our remarks began. 



Alluvium of the Vaal and Orange Eivees, and possible sources 

 OF THE Diamonds. — ^The superficial deposits of the Vaal Valley (we 

 are told) consist, in some places, of a ferruginous unctuous soil, with 

 or without sand and pebbles ; at other places, of calcareous tufa, 

 with or without pebbles ; and elsewhere of drifting sand, or of clay 

 of various colours. These lie either over gravel or on tufa, or on 

 the basalt,* conglomerate, or other bottom-rock. Superficial out- 

 spreads of pebbly gravel are frequent, with or without any of the 

 foregoing. Eidges of shingle also occur ; and sometimes angular 

 quartzose graveP appears to predominate. Of what the stratified 

 conglomerate (mentioned above as a bed-rock) consists is not stated ; 

 but the shingly deposits on the surface, whether loose or cemented 

 with iron-oxide, are mainly composed of more or less rolled frag- 



1 Geol. Trans., 2iid ser., vol. vii., p. 57 ; 1845. 



^ Geol, Mag., Vol. Ill,, p. 88, etc. 



^ In a paper lately read before the Geological Society of London. 



* The basalt is said by some to be a very different igneous rock from the abundant 

 greenstone of the country to the south and south-west, 



^ Dr. J, Shaw remarks that the angular quartz gravel is said to be bad groun 

 for diamonds ; and that the pebbly alluvium is better for the finders. 



