384 ORIGIN OF THE GRAVEL TERRACES 



of marine shells from so large an area of the gravels 

 from the Knysna district westwards while they are so 

 well preserved in the raised beaches seen in the Uiten- 

 hage district. The fact that on the coast of Van Rhyn's 

 Dorp gravels with marine shells overlie, and apparently 

 have been converted into, ferruginous and siliceous con- 

 glomerates, 1 does not imply that all the quartzitic 

 gravels at much higher levels in the south and west of 

 the Colony have suffered a similar change. The occur- 

 rence of the Knysna beds described in this chapter com- 

 plicates the problem, but at the same time makes it 

 improbable that the area in which they occur has been 

 submerged since their deposition. 



It seems more likely that the high level plains outside 

 the mountains, as well as those within, have been cut 

 by rivers, and that their dissection is due to their sub- 

 sequent elevation and the downward cutting of the 

 rivers. The raised beaches at heights of 100 feet or 

 more above the sea may represent the shore deposits 

 that were formed at the same time as the plains farther 

 inland. 



In the country north of the Orange Kiver surface 

 quartzites have a wide though far from uniform distri- 

 bution. In Griqualand West they have only been re- 

 corded from a few spots on the eastern flank of the 

 Langebergen." In Bechuanaland, on the other hand, 

 they are widely distributed at least as far west as Kuis 

 on the Molopo, but they have not been found on the 

 Kuruman River below Tsenin, the Mashowing below 

 a point a few miles from Madebing, on the Hygap, nor 

 1 G. C., viii., p. 161. 2 G. C., xi., p. 74. 



