438 W. M. DAVIS OBSERVATIONS IN SOUTH AFRICA 



In so far as I have been able to gain information as to the dissection 

 of the plain around its margin, it is of a kind that is equally consistent 

 with the central up-warping of a former low lying peneplain, or with the 

 marginal down-warping of an extensive area of arid leveling. The head- 

 waters of various rivers that rise in the southern part of the Veld and flow 

 southward across the Karroo and through gaps in the Cape Colony ranges 

 to the southern coast seem to have eroded normal valleys of moderate 

 depth beneath the highland. The retrogressive headwaters of the east- 

 ern slope have been described in previous sections as energetically occu- 

 pied with the capture of quiescent headwaters from the Orange Eiver 

 system. But this is also just what might have been expected under the 

 supposition of marginal down-warping after extensive arid leveling. It 

 is, of course, possible that the fuller description of the lower course of the 

 Orange river may give some light on this obscure point. It is known 

 that falls occur in the lower course of the river, as already mentioned ; but 

 the relation of the falls, and of the gorges that are presumably associated 

 with them, to the uplands and highlands is not yet made out. 



There is, however, one decisive test which, when applied, would suffice 

 to determine whether the Veld and the associated highlands — that is, the 

 great interior mass of South Africa — has suffered a change of altitude 

 with respect to sealevel since it was reduced to its present small relief. 

 This test is the occurrence of indisputable marine strand lines around 

 the continental margin. Such marks of a former seashore are reported 

 by Schwarz as occurring along the southern coast in the neighborhood of 

 Port Elizabeth at altitudes of from 200 to 400 feet. A sea-cut bench 

 at that altitude is described as being "covered with undoubted marine 

 shingle . . . sometimes associated with shell-deposits characterized 

 by a large Petuneulus" (c. 74). As to the occurrence of similar high 

 level sea margins in Natal where they would be more directly applicable 

 to the problem in hand, I have no information. They should be sought 

 for, inasmuch as it is evident that they bear critically on the conditions 

 under which the erosion of the Veld was accomplished. But it should 

 be pointed out in this connection that the various "plateaus" or evenly 

 eroded uplands of subaerial origin, now more or less dissected by rivers, 

 which are reported in association with the Cape Colony ranges, are not 

 decisive witnesses in this respect ; for they may have been eroded at their 

 present altitude with respect to a distant shoreline before the sea was 

 brought in to its present position by down-warping or down-faulting of 

 the lost borderland of the continent. 



