THE RAINFALL 153 



rising to 60 inches in very wet seasons. There are 

 also indications that much heavier rains have fallen in 

 the far distant past, but it would be hard to account 

 for this present decreased volume by anything for 

 which man may be held responsible. In portions 

 of Central Africa with which 1 am familiar, the 

 rainfall has, without question, greatly decreased 

 by reason of the wholesale destruction of the forests 

 which attracted it. The natives cut down the trees 

 over a considerable area, and, as soon as the trunks 

 are sufficiently dry for the purpose, set fire to them, 

 the resulting piles of snowy ashes going far to 

 increase the richness of the soU. After having 

 gathered in one or two crops, the clearing is 

 regarded as exhausted, and a move is made to 

 another locality where again the forest is sacrificed. 

 I consider that this process of consistent denudation 

 which has been going on through the ages is re- 

 sponsible for many an unproductive, arid waste, for 

 once destroyed, the greater forest growths have dis- 

 appeared for ever ; they are replaced by the smaller 

 stunted trees which are of no value as attractors of 

 rain. This, however, cannot be said of the higher 

 elevations of the Barue, which are still covered 

 with an exuberant growth of forest. The trees, it 

 is true, are not, as a whole, very impressive in point 

 of size, but this is accounted for, as I have 

 previously pointed out, by the phenomenal unpro- 

 ductiveness of the stone dust which here does duty 

 for soU. 



The geological formation is not unlike that of the 

 region of Manica, of the Shir^ Highlands, and of 

 various other portions of the same volcanic plateau 



