190 DWYKA OUTLIERS 



the base of the Karroo system, and south of the Orange 

 Kiver they have a persistent though varying dip towards 

 the interior, so that they form a basin. On the east, 

 south, and west the form of the basin is due to folding, 

 but the gentle inclination of the northern portion may 

 be partly or wholly an original feature. 



The outliers of the Dwyka series in the folded belt 

 south of the Karroo are few in number. The chief 

 one is that which forms a semicircular area between 

 Worcester and Lange Vlei near Robertson on the down- 

 thrown side of the great Worcester fault. 1 The rocks 

 are of precisely the same general character as those 

 along the south of the Karroo, but the black shales have 

 in places been converted into graphitic slates. In the 

 Worcester district, as in the Karroo, the boulder-beds 

 rest upon the lower shales, and these again lie conform- 

 ably upon the Witteberg beds. The Worcester outlier 

 is about forty miles distant from the nearest part of the 

 main Dwyka area in the Karroo, and is particularly 

 interesting because it shows no sign of a change in the 

 nature of the beds or in the relationship between them 

 and the older rocks. In the small outlier at Robertson, 

 however, the lower shales are much thinner than usual. 

 With this exception these facts, together with the uni- 

 form character of the conglomerate and its mode of 

 occurrence, at least as far east as Grahamstown, war- 

 rant the assumption that the area of deposition of the 

 Dwyka series was not limited in a southerly direction 

 within the boundaries of the Colony. 



Outliers of Dwyka have also been found at the head 



1 Schwarz, G. C., i., p. 27. 



