AN (EOOLOGICAL SURVEY OF THE MIDLANDS OF NATAL. 491 



gradations between smooth slopes and those Avhere the ground 

 is very broken. The vegetation varies accordingly. On all 

 the slopes soil transportation is going on rapidly, and the 

 plant associations are very mixed.^ There is a much greater 

 variety of veld grasses (Andropogon associations mostly) 

 as well as associated plants. But the types of plant formation 

 on these slopes do not depend entirely or even mainly on 

 edaphic factors. The climatic factors are equally important. 

 The south-eastern slopes, since they face the rain-bearino- 

 clouds and are sheltered from the hot dry winds of the north- 

 west, are often covered with bush, and when this is the case 

 soil transportation is checked, and we get a distinctly stable 

 type. On the other hand, the northern slopes, being fully 

 exposed to the hot winds, are often bare and rocky, and so 

 much so that the grasses cease to be dominant and we find 

 instead various xerophytic trees and shrubs (rocky hillside 

 formation). The two sides of the hill, therefore, are found to 

 diifer markedly in soil conditions and in plant formations. 

 These differences are brought about by the large rainfall, the 

 fact that climatic factors are unfavourable to the close type 

 of bush formation on the northern side, and the consequent 

 greater amount of soil transportation on that side. 



At the upper end of the valleys of the streams and smaller 

 tributaries we often find bush (close type) if the exposure 

 is towards the south or south-east. In many such valleys, 

 however, the bush has been destroyed and other plant asso- 

 ciations replace it. In stream-valleys that have not the 

 proper exposure for bush, the sides of the valley are grass- 

 land (Andropogon association), while the stream-channel 

 is bare and rocky. When a stream reaches more level ground 

 it frequently spreads itself out so as to form a marsh or vlei 

 and we may find a series of them along its course. 



At the foot of the slopes where drainage is checked there 



is frequently an iron-pan formation. Iron salts carried down 



in solution (in the form of the bicarbonate probably) are 



deposited as oxide of iron when the water dries up, as it does 



1 Loc. cit., p. 258. 



