THE VELD AS A PLAIN OF LEVELING 439 



The possibility of arid leveling may now be considered in relation to the 

 Veld. 



THE VELD REGARDED AS A PLAIN OF ARID LEVELING 



If the highland of the Veld be regarded as part of a region of arid 

 leveling essentially at its present altitude, the whole region must surely, 

 while the processes of leveling were going on, have had a much larger 

 continental area than that of South Africa at present; for the theory of 

 arid leveling at altitudes independent of the general baselevel of the ocean 

 necessarily presupposes that the leveling processes acted over an area so 

 large that the headward erosion of outflowing, peripheral rivers could not 

 make itself felt. If the area concerned were small, the capture of the 

 interior drainage systems by the peripheral rivers would permit the gen- 

 eral degradation of the arid area with respect to normal baselevel before 

 it could be leveled at some independent altitude, and thus only an ordi- 

 nary peneplain would be produced. The highland of Tibet may be ad- 

 duced in illustration of this principle. Before the mountains and basins 

 of that lofty interior region can be worn down to a continuous rock floor 

 of nearly level surface, the headwaters of the steep outflowing Indian 

 rivers will have retrogressively gnawed into the plateau country and cut 

 it to pieces, preparatory to reducing it to a normal lowland but little 

 above sealevel, always provided that some new mountain-making disturb- 

 ance does not invade the region and thus introduce a new cycle of erosion 

 under different conditions of high and low land from those now prevailing. 



It is therefore necessary, if we accept the theory of arid leveling, to 

 regard the Veld as only a large remnant of a once much larger highland 

 whose marginal parts have been warped or faulted down beneath sealevel. 

 This aspect of the problem will be considered in the next section. 



The large and well ordered Orange River system, already signalized as 

 very appropriate to an uplifted peneplain, is hardly consistent with the 

 conditions of arid leveling; for the later stages of an arid cycle are 

 thought to be characterized by the disintegration of the larger drainage 

 systems that might have existed during the maturity of the cycle. How- 

 ever, the occasional interruption of the actual drainage system by shallow 

 depressions or "pans" favors, or at least permits, the explanation of the 

 Veld by arid erosion, and if further study of the pans show them to be of 

 eolian origin, it may come to be concluded that the occurrence of a large 

 normal drainage system on the Veld today is the result of the coalescence 

 and slight modification of many formerly independent drainage systems, 

 in consequence of a change from a hypothetically more arid climate of 

 former times to a presumably more humid climate of recent times. 



