president's address. 21 



Harris, who travelled in the thirties and forties of last century 

 with wagons and had little difficulty in crossing the Limpopo and 

 other rivers as they came to them, do not suggest that there has 

 been a great change.'" 



The Middle Kalahari. 



It is beyond my purpose here to discuss the very incomplete 

 evidence we yet have about the existing features of the middle 

 Kalahari with the Makarakari and Ngami basins. They probably 

 are flat regions with ill-defined drainage, in which heavy rains 

 produce extensive flooding; they are probably typical results of 

 an arid climate, the duration of which is to be measured in 

 geological periods; had they been a country with heavy precipi- 

 tation throughout a long period of recent date, one would expect 

 a definite drainage towards the Zambesi, Limpopo or other direc- 

 tion to have been established, whereas there still seems to be 

 indecision, as instanced by the stoppage of the flow of the Tauche 

 by the reed rafts of the natives.'* The supposed recent drainage 

 of the area by the sudden opening of the Batoka Gorge is contra- 

 dicted by the gradually increased bevelling of the edge of the 

 gorge and the progressively increasing length of the tributaries 

 below the falls. '^ 



Conclusions. 



The conclusions these various lines of evidence point to are 

 that dui'ing post-Cretaceous times the climate of South Africa 

 has fluctuated within rather narrow limits ; that there has not 

 been a Pluvial period, if by that term is implied a long period of 

 much greater rainfall over the whole country; that a general 

 lowering of temperature in the Pleistocene may have given the 

 Karroo and Southern Kalahari rivers longer periods of flow, but 

 that this more humid era in those regions had come to an end 

 long before human evidence can be drawn upon for an account 

 of it; and that South Africa, like North Africa, the Americas and 

 Australia,*" bears witness to a shifting of the climatic belts in 

 Pleistocene and subsequent times. 



NOTES. 



(1) P. C. Sutherland, " On the Geology of Natal (South Africa), being 

 a Paper read before the Natural History Association of Natal, on the 

 •27th June, 1868." Durban, 1868. It is of interest to note that Dr. 

 Sutherland's opinion was supported and apparently prompted by Andrew 

 Ramsay's explanation of the Clent breccias of Permian age. which was a 

 mistaken one. The latest paper on the Karroo glacial ion is " The 

 Carboniferous Glaciation of South Africa," V)y Dr. A. L. du Toit, Trans. 

 Geol. Soc. S.A. XXIV, 188-227, a comprehensive summary of the facts and 

 an explanation on the lines of Wegener's hypothesis. 



(2) F. B. Taylor. " Bearing of the Tertiary Mountain Belt on the 

 Origin of the Earth's Plan," Bull. Geol Soc. America, XXI, 179-226. 1910. 



A. Wegener. " Die Enstehung der Kontinente und Ozeane," 1915, 2nd 

 edition, 1920; also a summary by that author in "Discovery" for May, 

 1922. 



