GENERAL 



197 



The western extension of the continent for thirty 

 degrees of longitude under the northern tropic, the 

 excessive heating of the atmosphere over the broiling 



?IG. 72. Mean Annual Rainfall of Africa. 



FIG. 73. Seasonal Distribution of Rainfall. 



Equator 



FIG. 74. Mean Temperature of Africa, reduced to sea-level. 



surface of that desert, and the existence of a sufficient 

 relief along the Guinea coast at sub-equatorial latitudes, 

 combine to produce a partly monsoon and partly 



