PEESIDE^-TIAL ADDRESS SECTION C. 61 



neigliboiiiiug' valleys, whereas imburned veld has a surface 

 moisture of its own, aft'ectino- not only the local dry-blanket, 

 but also improving matters in these neighl)ourino' valleys. 



A very marked case of moisture cut oft: by the ocean 

 T^inds being' intercepted by a mountain range is the Zambesi 

 delta, including the country from Inhambane to Mocambique, 

 which, being- screened from direct long distance ocean Avinds 

 by Madagascar, has a forest flora of an exceedingh- xerophytic 

 leguminous type up to the foothills of the mountains, a con- 

 dition one would hardly expect in such a climate as this area, 

 otherwise enjoys. 



Eaix from the Xorth. 



The rains coming from the north with the annual southern 

 journey of the sun and of the tropical cloud-belt act much in 

 the same way as those from off the sea {i.e., the moisture is 

 carried in a temperature and pressure which can maintain it 

 until cold air or mountains intercept, when rain falls or 

 moisture is deposited). In this way much of the country has 

 a perpetual dry-blanket, in a large area so arid that the name 

 Kalahari Desert has been applied to it, though not by any 

 means unfit to carry xerophytic vegetation, and it is a notable 

 feature that from Johannesburg to Pretoria northward and 

 westward hill slopes having northern aspects have better 

 ligneous vegetation than other slopes, which is the reverse of 

 what happens further south and east. But the presence of 

 that dry-blanket there, as elsewhere, usually brings rain in 

 torrents for a short time only, and seldom as a continuous drizzle 

 rain, when it does happen to rain. 



Xature of the Raixfall. 



The Senate Select Committee arrived at the conclusion : 

 " That all aA'nilable evidence goes to prove that there has 

 been no definite diminution in the rainfall of South Africa 

 during- historic times." But that there has been variation in 

 the distribution and nature of the rainfall is admitted, as also 

 increased desiccation. 



Nothing is proA-ed one way or the other in regard to the 

 total annual rainfall, nor can be for a long time, since the 

 long-period recording stations are mostly on or near the coast, 

 and in the south-west or in the Karroo, while the longest-period 

 station is the Royal Observatory, Capetown, which, being both 

 a coast station and one directly included in the south-west 

 winter rain area, is in no way affected by the eastern causes, 

 or by biotic influences at work throughout South Africa. 



But increased desiccation produces conditions less inducive 

 to rainfall and to repeated precipitation, and it is difficiilt to 

 conceive how desiccation can become more pronounced without 

 the rainfall in these dTy localities being affected also. 



The Senate Select Committee further states : " The evidence 

 as to the progress of erosion and desiccation has been most 

 definite, and the irresistible conclusion is that many parts of 

 the Union, in spite of the apparent constancy of the total 

 amount of the rainfall, have been slowly, but surely, drying 



