THE PLANT ECOLOGY OF THE COAST BELT OF NATAL. 371 



ia the Umzimkulu, Umzinto and Illovo valley!^, wliile now 

 and then domes of solid rock are seen rising out of relatively 

 even country. 



The Table Mountain Sandstone yields a rather pale grey 

 or pinkish open sandy soil with small white quartz pebbles; 

 this is distinctly poor and sour — a defect intensified by the 

 occasional development of a layer of hard lateritic ironstone 

 just beneath the surface. When the formation constitutes 

 a plateau, the smaller streams arising thereon generally flow 

 in shallow channels along which there are lengths charac- 

 terised by rocky bars alternating with sections possessing a 

 black, sandy and often boggy soil. 



The succeeding Dwyka Conglomerate varies greatly in 

 its surface habit. In its usual decomposed state it gives a 

 pale sandy to clayey soil with scattered boulders, and the 

 spheroidally weathering and buff-coloured crumbly rock 

 beneath is easily penetrated by the roots of trees, but on 

 ridges and steep slopes the conglomerate may crop out in 

 bare, grey slabby or hummocky surfaces, rough by reason 

 of the projecting inclusions, the rock being intensely hard 

 and dark blue in colour. In such situations the ground 

 tends to be treeless as on the 800-1000-foot plateau between 

 the Umkomaas and the Umpambinyoni rivers. 



The still younger blue (Lower) Ecca Shales, pierced by 

 dolerite sheets roughly following the bedding planes, crumble 

 away on the other hand to drab chocolate or red clayey soils, 

 while the succeeding (Middle) Ecca "Coal Measures" give 

 paler, more open-textured and sandy varieties. The dolerite 

 sheets penetrating these two groups have a veiy marked 

 influence, firstly, in producing a more fertile soil, either deep 

 red in colour or blackish, powdering when dry, but tenacious 

 when wet, and secondly, by reason of its water-storing 

 qualities in keeping the soil moist, the soakage from the 

 rainfall making its way along the contact of the decomposed 

 and jijinted igneous rock with the underlying indurated 

 shales. This is so frequently the case that the course of such 

 a sheet on a hilly and overgrown area can, not uncommonly, 



