TERTIARY AND RECENT DEPOSITS 383 



zone, from T V inch to 4 inches thick, is ferruginous and 

 brown in colour. The appearance of the rock gives one 

 the impression that it was formed by silica replacing 

 clay and iron oxides in the laterite, the fragments of 

 quartz, derived from veins in the Malrnesbury beds, re- 

 maining where they lay. No outcrops of the quartzite 

 were seen in the neighbourhood, which is a plain very 

 slightly above the level of a small stream bed a few 

 hundred yards away. 



This summary of the distribution and features of the 

 high-level gravels and associated rocks shows that 

 throughout the southern, western and south-eastern 

 portions of the Colony there are gravels and alluvial 

 deposits, altered to some extent by the deposition of 

 silica and other cementing substances between the 

 grains, lying high above the levels at which similar 

 accumulations are being formed at the present day. 



The origin of these gravel-covered plains has been 

 attributed both to marine and to subaerial erosion. 

 Prof. Schwarz l has given reasons for believing that the 

 parts outside the Cederberg-Langeberg Kanges were cut 

 by the sea, but that the terraces and plains east and 

 north of the ranges are due to river erosion at a time 

 when the country as a whole stood at a lower level than 

 now. The chief reason for postulating marine erosion 

 for the outer plain was that it is difficult to understand 

 how streams could cut such a uniformly narrow shelf 

 as is found along the George and Knysna coast. It is 

 difficult, however, on this view to explain the absence 



1 Q.J.Q. S., Ixii., p. 70; Geographical Journal, March, 1906; Am. 

 Journ. Sci., vol. xxiv., 1907, p. 186. 



