542 J. w. I5KWS, 



largel}^ to be explained on these grounds. Though most soils 

 in Natal are fairly poor in lime, the low-veld soil where the 

 Acacia species occur is much richer in that element than the 

 others. It is, to a large extent, alluvial in its origin, and the 

 lime, which has been dissolved out of the soils at higher 

 altitudes in the dry river-valleys, is reprecipitated, often in 

 the form of small nodules. 'J'he absence of the thorn -trees 

 from the high veld of the Midland region may also be 

 explained in the same way. 



3. ROCKY SCEUB. 



Very commonly the dominant tree in the Rocky Scrub is 

 Grreyia sutherlandi (Baakhout). This Greyia association 

 occurs in small clumps, which are often quite isolated and 

 surrounded on all sides by typical veld or Protea veld. 



The ground is very broken, the geological conditions being 

 of the most unstable type. There are often huge boulders 

 and projecting masses of bare rock, around which the soil 

 accumulates. 



Typical rocky scrub has the following composition : Greyia 

 sutherlandi, Aloe natalensis, Royena lucida, R. 

 cor data, Euclea undulata, Cliffortia linearifolia, 

 Celastrus spp., Passerina ericoides, Buddleia sal- 

 viasfolia, Phygelius capensis, Osteospermum moni- 

 liferum, Sparmannia palmata, Cussonia spicata, 

 C. paniculata, Osy ridocarpus natalensis, Hippo- 

 bromus alatus, occasional members of the Oudehout scrub 

 described below, and a greater or less admixture of the 

 herbaceous and shrubby species named above as occurring 

 on the barer or rocky patches of the veld (Class B of 

 associated veld plants, p. 537) and being transitional to 

 Rocky Scrub. 



The Proteas are often immediately adjoining in the veld, 

 but they do not mix Avith the Greyia association (text-fig. 1). 

 The Rocky Scrub of the lower zone has many points of 

 similarity with the talus and ravine vegetation of the upper 



