432 ME. W. GIBSON ON THE GEOLOGY OF THE GOLD-BEAEING 



are covered up. Farther on along the same road — three stages 

 from Potchefstroom — horizontal olive shales and some sandy beds 

 are exposed on the roadside ; they are probably of Karoo age. 

 Volcanic country again prevails as far as Potchefstroom. 



On the banks of the Vaal, at the farm called Strykfontein (see 

 PI. X. fig. 1), 35 miles south of Johannesburg, thin conglomerate- 

 bands and quartzites are shown dipping northwards at a low angle; 

 it is said that these reefs can be traced as far as Heidelberg. 

 Following the banks of the Vaal in the direction of the stream, a 

 thick sheet of compact undecomposed basalt soon conceals every- 

 thing. 



2. The Yredefort and FotcJiefstroom Districts. 



Crossing the Yaal Eiver at Vaal Pont, and going in a direction a 

 little to the west of Heilbron, we find gently undulating, grass- 

 covered prairie land extending on either hand as far as Vredefort. 

 Outcrops are very rare ; where the rock is seen it is almost invari- 

 ably of an igneous character. But in one spot, about 6 miles 

 from Vaal Pont, in a S.S.W. direction, a section is exposed of con- 

 glomerates dipping at an angle of a few degrees to the west. As at 

 Strykfontein, however, the strata are soon buried beneath igneous 

 rocks. "West of Vredefort, and in the immediate vicinity of the 

 town, gneisses, schists, granites, and gabbros form the low hum- 

 mocky ground, and large blocks of these crystalline rocks are scat- 

 tered about the town and its neighbourhood. Possibly these blocks 

 may be erratics ; but it is much more probable that they are simply 

 unweathered fragments of the underlying rocks. One fact bearing 

 out this conclusion is that after travelling for about 4 miles to 

 the west of Vredefort the ground rapidly rises into high and rugged 

 hills, which are found to consist of quartzites and conglomerates, 

 dipping at a very high angle to the west. This looks as if some 

 disturbing influence had acted in the neighbourhood ; and from what 

 we know has happened on the Randt, as well as from other evidence, 

 it seems reasonable to believe that the quartzites have been pushed 

 up against a bank of crystalline rocks. So far as the writer is aware, 

 there is no evidence of glaciation so far north in South Africa. 



The hills just mentioned as lying west of Vredefort present 

 precipitous slopes and bristling hog-backed summits ; the beds of 

 which they are composed are admirably displayed, and their twists 

 and curves are easily traceable by the eye for several miles along 

 the strike, which is roughly north and south. For some distance 

 westwards the dip continues to average nearly 90° ; but farther on 

 in the same direction it is slightly less and to the west. This high 

 dip is continued as far as Lindequisfontein, a distance which may 

 be roughly estimated as 10 miles. Here the strata again form high 

 hills, but the dip, although still high, is now to the east. Up to 

 Lindequisfontein the beds are composed of red shales and quartzites, 

 with here and there a thin conglomerate-band. The whole series is 

 identical with the Quartzite-and-Shale Group lying beaeath the 

 Main Eeef. 



