RELATION OF RIVERS AND RIDGES 429 



ing of the plain above the notch, followed by aggradation, or an undue 

 supply of waste in excess of that which could be carried through the notch. 

 The plains and the ridges, the stream channels and the notches, are essen- 

 tially such as one might expect to occur in the undisturbed old age of a 

 region of hard and soft rocks in a subarid climate, and hence we are war- 

 ranted in supposing that erosion has been steadily in progress on the Veld 

 for a long time in the past. However the river courses were originally 

 determined, they must have been running practically on their present 

 courses during at least the greater part of the period in which the later 

 erosion of the plains has been accomplished, and during that period South 

 Africa appears to have been an undisturbed land area. 



PENEPLAINS IN OTHER PARTS OF SOUTH AFRICA 



The condition of long enduring continental quietude indicated by the 

 peneplanation of the Veld appears to have obtained in other parts of 

 South Africa as well. On our way northward from Mafeking we passed 

 through a granitic district on the eastern border of the Kalahari where 

 the general relief was small and where the watercourses were slightly, if at 

 all, incised in the broad and shallow depressions that sank beneath the 

 broad and gentle swells, as on the Veld. Occasional knobs and moun- 

 tains — "Inselberge," as they have been called by German explorers — rose 

 above the plain. Farther north, around Bulawayo, the steeply inclined 

 schists are truncated in a broad, gently undulating plain; but here the 

 watercourses were rather more distinctly incised than in the other dis- 

 tricts named. Not far from Bulawayo is a group of granitic hills, known 

 as the Matopos and famous as holding the grave of Cecil Ehodes at the 

 summit of one of their higher eminences ; they are monadnocks of granite 

 that rise above the surrounding peneplain of schists. A small example 

 is shown in plate 49, figure 2. Again, on approaching Salisbury, the 

 capital of Rhodesia, we crossed a gently undulating plain eroded on in- 

 clined rocks and interrupted by a pronounced ridge of nearly vertical 

 strata, apparently quartzites, through which the railway passed in a sharp 

 notch. East of Salisbury the undulating plain seemed to be worn down 

 on granite, which often rose in local knobs and heaps of weathered 

 boulders like small Matopos. We were told that the railway line from 

 Bulawayo to Salisbury was laid nearly along the water-parting between 

 the Zambesi and the Limpopo, so as to avoid the valleys of the larger 

 branches, which are more and more deeply incised beneath the highland 

 as the main rivers are approached. 



The reports of two explorers may be cited to show the existence of ex- 

 tensive peneplains farther north and northwest. For example, Born- 



