444 W. M. DAVIS — OBSERVATIONS IN SOUTH AFRICA 



or the less ancient date for the origin of the eastern and southern coast- 

 line accords better with the amount of erosion that has since then been 

 accomplished on the coastal slopes. 



CONCLUSION AS TO THE ORIGIN OF THE VELD 



The alternatives thus presented are clearly enough separated as far as 

 their mental conception is concerned ; but, in our present ignorance of the 

 rate at which retrogressive erosion goes on, it seems hardly possible to 

 make choice between the two possible conditions under which the plana- 

 tion of the Veld took place. If a comparison of the Veld with the Ari- 

 zona plateaus is legitimate, the result of the comparison would be in favor 

 of a later date than Cretaceous for the initiation of the eastern escarpment 

 or continental slope from the Veld to the Indian ocean; for if a wide- 

 spread erosion, reducing a great extent of country to a lowland (afterward 

 elevated to plateau altitude), took place in Arizona in post-Eocene time, it 

 would be expected that a great reduction of a highland would have taken 

 place in Natal in both Cretaceous and Tertiary time. It is true that the 

 rocks are not the same in the two regions ; but, as far as the comparison 

 enables one to judge, the erosion of the eastern escarpment of the Veld is 

 less than might be expected for the work of much of Cretaceous and all of 

 Tertiary and post-Tertiary time. For this reason, as well as for that 

 based on the features of the Kongo basin, it seems improbable that the 

 erosion of the Veld was accomplished by the processes of arid leveling at 

 its present altitude. It is, however, still conceivable that the Veld is the 

 product of arid erosion while the continent stood at a less altitude than 

 that of today, and that the arid plain has been elevated and its discharg- 

 ing marginal rivers have been revived in the manner described for the 

 case of a normal peneplain. No decisive choice seems possible at present 

 among these baffling alternatives. 



Continental Analogies 



The preceding paragraphs suggest a brief reference to a favorite topic 

 among geographers, namely, the greater or less resemblance between dif- 

 ferent continents, which has often been taken to reveal something of the 

 plan of continental construction or even of terrestrial deformation. Anal- 

 ogies of this kind were pointed out long ago, before much was known of 

 geological structure. They were then based chiefly on continental out- 

 line, with a brief supplement of gross continental topography. With the 

 progress of geological study, some of these analogies have gained support, 

 others have been shown to have little or no foundation, while some new 



