430 W. M. DAVIS OBSERVATIONS IN SOUTH AFRICA 



hardt (27-29)* describes the uplands between Lake Nyassa and the east- 

 ern coast as consisting of gneiss, generally reduced to a surface of small 

 relief, but here and there surmounted by residual eminences, or Insel- 

 berge. Passarge (a, 636-638) says the same of large areas of the Kala- 

 hari Desert area. 



The various peneplains here referred to can not at present be surely 

 correlated as belonging to the same cycle of erosion, but there is a pre- 

 sumption that they are of similar dates of development, and they certainly 

 all agree in testifying to the quietude of the continent for a long time 

 and over a large area. 



DISTRICTS OF STRONGER RELIEF 



Although a great part of the South African highland may be described 

 as made up of undulating plains and accounted for as the result of long 

 continued, penultimate erosion, there are certain districts where the relief 

 is hilly or submountainous. The Stormbergen, for example, which lay 

 southeast of our route across the Veld, are several thousand feet higher 

 than the highland. They are built of the youngest members of the Karroo 

 system, reinforced by abundant sheets of dolerite. They are believed 

 to be residual eminences that have survived the erosion which has swept 

 away the less fortified strata elsewhere. In the neighborhood of Pretoria 

 there are several well defined ridges, the greatly denuded edges of various 

 resistant formations belonging to older geological systems than the Kar- 

 roo. The famous Hand or escarpment at Johannesburg is another exam- 

 ple of the same kind. The moderate relief to which these ridges are re- 

 duced from the former much greater extension of their strata is the result 

 largely of pre-Karroo erosion, partly of post-Karroo erosion. North of 

 Kimberley we saw a long even-crested escarpment in the distance to the 

 west of the Vaal river. North of Maf eking the railway passed among 

 a number of subdued mountains believed to be composed of the same 

 formations as those about Pretoria, as shown on the valuable geological 

 map of the Transvaal, by P. H. Hatch, in Hatch and Corstorphine's 

 Geology of South Africa. The Inselberge on the eastern border of the 

 Kalahari and the Matopos near Bulawayo have already been mentioned. 



* The explanation that Bornhardt here offers for the even surface of the upland which 

 he describes does not seem satisfactory. He supposes that the region concerned, once 

 surmounted by additional rock masses and therefore rising to a greater altitude, was 

 dissected to maturity and then depressed and buried under later sediments and again 

 elevated ; and that by several repetitions of this process a number of independent 

 criss-crossing valley systems were developed, so that their confluent floors would form a 

 plain, while the intermediate spaces were left rising in isolated knobs. The difficulty 

 here is that in the successive periods of elevation and erosion there is no guarantee that 

 the land mass shall resume the same altitude, and hence no reason for thinking that the 

 space between the knobs should be reduced to a single plain. 



