8o SCIENCE IN AFRICA 



Territories are dealt with by Raeburn and Brynmor Jones (1934) 

 in their volumes on the Chad basin. 



The question of water-supply in the north of the Gold Coast has 

 not yet been investigated, except during a preliminary survey of 

 conditions by Mr. Cooper, one of the government geologists. The 

 conditions there are in some ways similar to those of northern 

 Nigeria, since the agricultural progress of a large population is 

 held back for want of water. It is interesting to note that the 

 veterinary department at Pong-Tamale has opened up several 

 billigers or water reservoirs used by a former native civilization in 

 the northern Gold Coast. These are caverns hollowed out in 

 impervious strata below a hard layer of laterite concretions, a few 

 feet thick, at ground level. During the rainy seasons the caverns 

 are flooded, and the water can be drawn upon for domestic pur- 

 poses and for stock. Billigers are known over a large area, and, 

 though entirely disused and choked with earth and debris, their 

 renovation may contribute materially to the welfare of cattle- 

 owning peoples in that district. 



In French West Africa the public works department, with 

 advice from geologists, has worked steadily at well-sinking, in the 

 Sudan and Niger colonies along the southern border of the Sahara, 

 Moreover, the great irrigation developments on the Middle Niger 

 at Macina and Sotuba have necessitated a full organization for 

 hydrographic studies, and the Office du Niger maintains a staff 

 of experts. M. Belime, the Director of the office, has published 

 (1928) a short account of early work on the Middle Niger. For 

 the past ten years or so the levels and flow of the Middle Niger 

 have been fully recorded as a preliminary to the great engineering 

 works now in progress, but the results have not yet been pub- 

 lished. 



In other parts of French West Africa, E. de Martonne (1928) 

 made a study of the upper Gambia, and more recently A. Minot 

 (1934) and others have studied the Senegal River in detail with a 

 view to irrigation schemes. Colonel Tilho, whose work is referred 

 to in Chapter IV, has also contributed much data on the hydro- 

 logy of the Niger, Senegal, and Lake Chad basins, and he has 

 shown how several of the major water-courses in this part of Africa 

 have been profoundly changed in recent geological times. It is 



