SOME PROBLEMS OF RESEARCH 5 



Niger may be cited; vast areas of desert country are there being 

 put into intensive cultivation by the construction of barrages and 

 feeder canals, but there is no settled agricultural population in the 

 immediate neighbourhood. It is necessary, therefore, to convert 

 nomad pastoralists into fixed cultivators, and it is even proposed 

 to transplant some of the dense population of Algeria to this region, 

 separated as it is from their home by the Sahara Desert. Other 

 schemes have been suggested in the native reserves of East Africa; 

 for example a recent study of the Tana River showed how a large 

 area, at present ravaged by soil erosion, could be changed into 

 a centre of permanent settlement by an irrigation work. It is signifi- 

 cant here that nothing further can be done until the whole region 

 is mapped to a degree of accuracy far surpassing that of the present. 



Another question in which the measurement of Africa's surface 

 is all important, is that of the exploitation of mineral resources. 

 The momentous changes in environment which this has made are 

 more prominent in southern Africa than elsewhere, but there is 

 no reason to suppose that the rocks of South Africa are more rich 

 in valuable minerals than those of the tropical regions. The 

 greater degree of change so far produced in South Africa is due 

 solely to the greater efforts that have there been devoted to the 

 discovery of minerals. 



Of all environmental factors, water-supply is the most impor- 

 tant because it controls all plant and animal life. In general the 

 character of vegetation and the crops which can be raised are 

 determined not by the total rainfall so much as by its distribution 

 through the year. Thus the double maxima of rainfall occasioned 

 by the type of atmospheric circulation in tropical latitudes, where 

 the sun passes vertically overhead twice during the year, involve 

 a double climax in vegetable growth, and hence in agriculture. 

 Local climatic conditions, however, sometimes obliterate one of 

 the rain maxima in certain areas, such as the belt of country 

 between the Guinea lands and the Sahara, which includes the 

 French Sudan, the northern parts of Nigeria, the Gold Coast, 

 Dahomey, etc. In all this belt, human activity follows a single 

 cultivation cycle during the year. We can state that in any given 

 set of conditions which are constant from year to year, an agricul- 

 tural or pastoral people will evolve suitable methods of cultivation 



