526 J. W. BEWS. 



4. THE PLANT FOEMATION ON EOCKY HILL-SIDES. 



(1) High Veld Region. 



This formation is found on the steep slopes which face 

 north, where the climatic factors are unfavourable to the 

 growth of the close type of bush. It is fully exposed to the 

 hot, dry winds from the north or north-west. The trees 

 which compose it are more xerophytic than those of the close 

 bush, but less so than those of the thorn veld. OEcologi- 

 cally it may be taken as intermediate between thorn veld and 

 close bush, but here the determining factors are mainly 

 climatic. The topography is very similar to that of the close 

 bush formation, though soil transportation is less checked, 

 and therefore the slope is more rocky, being more denuded. 



The trees grow sometimes isolated, sometimes a few together 

 forming small clumps. They suffer less from fires, for they 

 possess a notably thick bark which protects them. The 

 grasses are also not so luxuriant as in either the high veld or 

 the low veld, and when they are burned the fires are not so 

 destructive. In fact in many cases the grasses are so poor 

 that they are not burned. This poorness in grasses leaves 

 the soil still more exposed, and the slope is very often rugged 

 and broken, being cut through by ravines or dongas. The 

 grasses that do occur are the Andropogon associations that 

 clothe the other slopes, with a mixture of Aristida junci- 

 formis, and the various associated plants. 



Though the slope as a whole is very dry, there may be a 

 few springs or wet spots, and there are commonly dry stream- 

 channels which are filled with water only after a rainstorm. 

 Large and small blocks of dolerite are a common feature of 

 such slopes. These check soil transportation, and conserve 

 moisture. If in the driest, hottest weather a stone is raised, 

 the ground underneath will be found to be slightly damp. 



This variability in the soil conditions (in particular as 

 regards its moisture) is reflected in the vegetation. While in 

 the thorn veld where the soil is uniformly very dry there 



