AN (ECOLOGICAL SURVEY OF THK MIDLANDS OF NATAL. 489 



I. THE REGIONAL FACTORS. 



1. Edaphic Factors, 



The area dealt witli in this survey inchides roughly about 

 450 square miles, and may be taken as typical of the Midlands 

 of Natal. 



The rising ground to the west of Pietermaritzburg is com- 

 posed of Coal Measure Sandstones and arenaceous shales 

 (high veld). On the lower ground to the east, Ecca Shales 

 are exposed and mostly lie very near to the surface (low veld). 

 Below these is the Dwyka Conglomerate exposed at various 

 places near Pietermaritzburg (low veld). To the extreme 

 east of the area surveyed Table Mountain Sandstone appears 

 (high veld or transitional). 



The whole area is cut thi-ough everywhere by dolerite 

 dykes and sills, and the weathering of these adds greatly 

 to the fertility of the soil. 



While it is not difficult to find plants that are characteristic 

 of each of these geological formations, yet any attempt to 

 base any oecological classification on them must necessarily 

 fail, since the other factors — which in Natal are especially 

 important — must be taken into account. It is Avell also to 

 keep in mind the fact that the soil may bear little or no 

 relationship to the rocks immediately underneath. This is 

 particularly the case in the low veld. 



Of course the general topography of a country is determined 

 ultimately by the geological structure, and it is hoped that 

 throughout this paper due attention has been given to the 

 influence of topography in determining the plant formations. 



The general positions of the various geological strata have 

 been marked on the vegetation map. The detailed explana- 

 tion of the map is given at the end of this paper. 



The area is drained by the Umgeni river and its main 

 tributary, the Umsindusi. As in all other parts of Natal, 

 denudation is going on with extreme rapidity. The area 

 forms a portion of the second main terrace, but the Zwaartkop 



