THE PLANT ECOLOGY OF THE COAST BELT OF NATAL. 369 



formed part of the work done for the Botanical Survey of the 

 Union, recently instituted under the directorship of Dr. I. B. 

 Pole-Evans. 



The following section on the geology, topography, and soil- 

 conditions has been very kindly supplied by l)r. A. L. du 

 Toit, who has carried out the recent detailed geological 

 survey of most of the coast belt. 



I. GEOLOGY. TOPOGRAPHY, AND SOIL-CONDITIONS. 



The hundred and fifty miles of low-lying coastal belt in 

 Natal possess a wondei'ful uniformity, which can in part be 

 accounted for by the fact that climatically there is little 

 variation from south to north within this stretch of country. 

 The straight north-easterly trending coast-line, broken only 

 by Port Natal, has been determined mainly by down-warping 

 of the seaward side of Natal in Cretaceous times along a 

 nearly parallel hinge-line, situated some distance inland, such 

 having been accompanied b}' minor folding and by con- 

 siderable faulting in the coastal portion. The sculpturing 

 of the surface is of the same pattern throughout, and the 

 general slope for a short distance back has a value of between 

 Ih and 3 degrees, so that the thousand-foot contour is attained 

 within from 5 to 10 miles usually, though the gradient over the 

 next thousand feet is less. The rivers are ai'ranged at right 

 angles to the coast-line, and taken in order from south to 

 north consist of the Umtamvuna, Umzimkulu, Umzumbi, 

 Umtwalumi, Umzinto, Umkomaas, Illovo, Umlazi, Umgeni, 

 Umhloti, Tongaat, Umvoti and Tugela. They have cut deeply 

 into the general surface and flow in picturesque gorges, 

 between each pair of Avhich the ground generally rises rathei- 

 regulai^ly inland, advantage having been taken of this fact 

 in the construction of roads and railways. Occasionall}^ 

 ground belonging to the coastal belt and well below the 

 thousand-foot contour is partially or wholly severed from 

 the dissected plateau inland, as, for example, within the 

 Umtwalumi valley. 



