112 SCIENCE IN AFRICA 



while the British Isles were buried under ice, the Sahara was in 

 large measure green, populous, and fertile. At the same time the 

 snow-line on the equatorial mountains was much lower than at 

 present, the drainage systems were strikingly different, and the 

 equatorial lakes were very much larger than now. Furthermore, 

 it has been shown, especially in eastern Africa, by the work of 

 Wayland (1935), Leakey (1931 and 1935), and Nilsson (1935), 

 that the pluvial epoch was not a continuous time of intensive 

 rains and snows, but was divided into a series of pluvial periods 

 separated by arid interpluvials when the climate was much drier 

 than it is to-day. The importance of these arid periods, especially 

 in relation to past and present fauna, has been stressed by Fuchs 

 (1934) and Worthington (1933). 



A question of significance for the study of changes in climate 

 throughout the world, is whether the series of pluvial periods in 

 Africa were contemporaneous with the series of glacial and inter- 

 glacial periods in the northern hemisphere. This question is not 

 yet settled. It has been discussed by several authorities, notably 

 by Brooks (1931). Whether the desiccation that has since over- 

 taken the Sahara and affected all equatorial Africa is yet com- 

 pleted on the geological time scale, we have no definite means of 

 knowing, but several experts are of the opinion that Africa is even 

 now emerging from the last pluvial period, and is still undergoing 

 a steady change to drier conditions, though not without oscilla- 

 tions and temporary damp phases. Wayland and Leakey in 

 particular reach this conclusion from their studies of prehistoric 

 climates in Uganda and Kenya. On the other hand, J. D. Falconer 

 (1911 and 1937), who has discussed the geological evidence for 

 climatic change in Northern Nigeria, concludes that the desert 

 pulsates with an expansion and contraction of its margins and that 

 the most recent movement has been one of contraction, with the 

 consequent spread of more humid conditions over the country 

 between Lake Chad and the River Niger. This question is further 

 discussed in the next section. 



Turning to changes in climate on a smaller scale, which may be 

 recognizable in the records collected since the European came to 

 Africa, there is also a considerable literature, some of which is 

 referred to in a valuable paper, devoted mainly to the European 



