TERTIARY AND RECENT DEPOSITS 393 



the sand comes to lie in places where it occasionally 

 remains wet for some time, as in pans and the beds of 

 rivers. 



The most remarkable patch of white sand in the 

 country is at Witsands, 1 west of the Langberg in Hay ; 

 the sand there is pilled up round ridges of quartzite, 

 and in low-lying spots between the sand-hills water is 

 found a few inches or feet below the surface according 

 to the length of time since the last heavy rain. In the 

 sand there are banks of laterite, occasionally exposed 

 through the removal of the sand by the wind. This 

 laterite presumably represents the iron oxides leached 

 out of the sand and deposited again near the surface. 



The sand in a large part of the Southern Kalahari 

 forms long dunes which may run parallel for more than 

 a mile or may converge and join together ; their trend 

 is between west-north-west and north-north-west, 2 but 

 near the river beds the dunes tend to lie parallel to them, 

 and they are also banked up parallel to parts of the 

 edges of pans. 



At the present time the sand in the Southern Kala- 

 hari is kept in its place by grass and other vegetation ; 

 bare sand is rarely seen away from the waggon tracks. 

 The largest areas of unprotected sand, which is then 

 easily moved by the wind, are along the Orange Eiver, 

 where the veld is most rapidly eaten off by stock. 



The average depth of the sand is not even approxi- 

 mately known. In the western part of Gordonia, where 

 the underlying rock is frequently exposed, the dunes are 

 often over 100 feet in height. In the eastern part of 



1 G. C., xi., p. 72. 2 See Map attached to G. C., xii. 



