170 



ME. G. W. LA.MPLTJGH ON THE 



[May 1907, 







****• 







\*\ 



«]»! 



Ill: 



district, especially south of the Zambezi, and appear to be still 

 more extensive in the shallow basins of the Kalahari. 



Much of the plateau between these grassy depressions is covered 



deeply by rusty-red sand, occurring 

 usually in broad gentle swells or 

 ' bults,' which may be a mile or 

 more in width and many miles long. 

 These sand-bults occur on both sides 

 of the Zambezi, but their propor- 

 tionate area increases southward as 

 the plateau merges gradually into 

 the true Kalahari. From their 

 capacity for retaining moisture these 

 sands nourish taller trees and more 

 vigorous vegetation generally than 

 the rocky portions of the plateau. 

 They are equivalent to the ' Kalahari 

 Sand ' of Dr. Passarge, and must 

 have been accumulated under cli- 

 matal conditions very different from 

 the present (see p. 201). 



On flat ground where the sand is 

 absent the surface is for the most 

 part thinly covered with a firm, rusty, 

 lateritic soil derived from the basalt, 

 through which protrude many blocks 

 of partly weathered rock. In some 

 places this soil, like the well-known 

 laterites of India, is full of small 

 hard pellets or 

 tions, about the size of peas. 



The appended diagram (fig. 1) 

 will serve to illustrate the physical 

 features which we found to be con- 

 stantly repeated in traversing the 

 plateau along the margin of the 

 newly-dissected country. 



There is a decided fall of the 

 JJ.xi"! surface of the plateau towards the 



Zambezi both from the north and 

 from the south, which appears to 

 xQ * : reflect its original structure ; and the 



*jx] x ; gradual sinking of the country east- 



ward until the Deka is reached is 

 probably also structural. Hence the 

 course of the Zambezi may roughly 

 coincide with an original depression 

 in the plateau, which has, of course, been greatly accentuated by 

 loner-continued erosion. 



ferruginous concre- 



o *g 



w~. 



