14 fresidhnt's address. 



species south of the mouth of Zand Leegte and about 100 feet 

 above the modern beach proves a recent date for the infilling of 

 that valley, and the only apparent initial cause is a decrease in 

 the rainfall in that region, though no doubt the accumulation of 

 sand over the catchment added greatly to the effect of decreased 

 rainfall by diminishing the run-off. 



In the Transvaal the minor valleys often head in kloofs part'y 

 filled with gritty alluvium or wash in which the present stream 

 bed is entrenched to considerable depths, 20 to 50 feet, without 

 exposing the bed rock of the valley. The Kloof at Heidelberg is 

 a good instance, and the stream leading to the Crocodile Eiver on 

 Wachteenbietjesdraai, in Eustenburg District, is one from country 

 only lately in permanent occupation by Europeans. A marked 

 effect of permanent occupation by whites is the destruction of 

 vegetation in stream beds, thereby giving freer scope to the 

 erosive power of the stream. So instances of the kind we are now 

 concerned with are not free from uncertainty, but the develop- 

 ment of the ravine in the kloof on Waehtenbietjesdraai can hardly 

 have been influenced in this way, and it points to an arid period 

 having fallowed the formation of the kloof and having brought 

 about its partial infilling by wash, which is now being removed by 

 a deeply entrenched periodical stream. 



Pans. 



Pans are found chiefly in dry regions, for in wet countries 

 any depression from which there is no outlet is eventually filled 

 in with mud and sand carried there by water, or else the 

 depression becomes part of a river valley. They are most 

 numerous in the drier parts of South Africa, and especially in 

 the dry country now occupied by nearly horizontal Karroo beds 

 or but recently stripped of them. In the Ghoup and Tanqua 

 Karroo, with an average rainfall of less than 10 inches, and where 

 the Karroo beds are inclined at various angles, there are no well 

 defined pans,^^ but in the northern Karroo of Calvinia, Carnarvon, 

 Prieska and Hopetown, where the rainfall is about the same and 

 the rocks lie flat, well developed pans are numerous, as they are 

 in the Western Orange Free State and the Southern and Eastern 

 Transvaal. In these latter regions the rainfall is higher than in 

 the Karroo, from 15 to 35 inches instead of from 5 to 15,^'' and 

 twelve years ago Professor Penck argued that the salt-pans of 

 the Transvaal and Orange Free State were formed when those 

 parts of the country had a drier climate than they now have, 

 because such depressions cannot develop in a humid climate.''* 

 The most remarkable pans in the Transvaal are those in the 

 Ermelo District, of which Lake Chrissie is the best known. 

 They lie entirely on Karroo beds, and they are on the great 

 watershed between the Vaal Eiver, the Komati and Usutu Elvers. 

 They are well defined pans, for the vegetation changes in 

 character within a few yards, while in the pans of the Northern 

 Cape Province the zone of change from pan-floor to outer veld 

 may be 100 yards wide. Many of the smaller pans support a 



