716 MR. E. K. KASTALL ON THE GEOLOGY OE [Nov. 10,11, 



Slate, with a dip totally different from that of the Witteberg Beds. 

 Hence it is certain that the main fault must cross the river very 

 near the drift. At this point the road turns northwards and runs 

 parallel with the river for some miles, over a monotonous series of 

 grey sandy nags and mudstones, with occasional bands of silvery slate 

 and soft olive-green shale. The strike of these rocks is about west 

 10° south, and east 10° north, and the dip is always southwards 

 at an angle varying from 20° to 50°. About half a mile north of 

 the drift is the band of dolomite previously mentioned (p. 715), and 

 close to it is a rather coarse grit, as also a very peculiar schistose 

 rock containing large blocks of black vein-quartz, which impart to 

 it a sort of augen structure. This appears to be a crushed con- 

 glomerate, since the blocks of quartz are certainly of detrital origin. 

 This may be compared with the conglomeratic band seen close to 

 the marble-quarry at Worcester, and it is just possible that they are 

 the same, since in each case the conglomerates occur in conjunction 

 with a calcareous band. 



Throughout this series cleavage and jointing are very conspicuous 

 in the finer beds, while the gritty beds show these structures less 

 perfectly. Vein-quartz is abundant almost everywhere, and always 

 shows a peculiar blue-black colour. The quartz-veins were evidently 

 injected before the final foliation of the Malmesbury rocks. 



Calcareous beds occur in several localities in the neighbourhood 

 of Robertson. The most important of these are on the farm 

 Dassies Hoek, where they are associated with black graphitic 

 shales. 1 Beds of dolomitic limestone are also seen on the Hoops- 

 River Road, and in Keur Kloof, north of the town ; the latter 

 occurrence was at one time worked for lime-burning. It is a dark 

 bluish-grey rock, which weathers in a peculiar manner, becoming 

 covered with a thick, pulverulent, white crust. A rough quanti- 

 tative analysis of this rock showed the presence of 10 per cent, of 

 matter insoluble in hydrochloric acid, G per cent, of ferrous car- 

 bonate, and 37 per cent, of magnesium carbonate, so that it is 

 correctly descrbed as an impure gritty dolomite. 



(2) The Granitic Intrusion of Wolve Kloof. 



This large mass of granite has a roughly oval form, and measures, 

 as at present exposed, about 4| miles from north to south and 

 2| miles from east to west. It forms conspicuously high ground, 

 and its central portion rises to a height of over 3100 feet above the 

 sea. The exact outline is difficult to determine, owing to the rugged 

 nature of the ground and a thick covering of vegetation on the 

 lower slopes. By far the best section is seen in Wolve Kloof, a deep 

 and narrow gorge formed by the Nels River, which cuts through 

 the granite for a distance of about 1| miles. The precipitous sides 

 of this gorge are formed of smooth rounded surfaces of granite , 



1 A. W. Rogers & A. L. Du Toit, ' Geology of Cape Colony ' 2nd ed. (1909) 

 p. 24. 



