244 EAST AFRICAN FLORA AND FAUNA part iii 



a paper on " The Glacial Geology of Mount Kenya," ^ which 

 deals with both the causes of the greater glaciation and some 

 of its results. The former has been referred to in a previous 

 chapter, but the latter must be considered in relation to the 

 changes in the flora. 



In the paper quoted it is shown that the glaciers once 

 extended for over 5400 feet below their present limits, and it 

 is suggested that this was due to the level of the whole country 

 having been much higher than at present. Whether this were 

 the cause or not, there can be no doubt that the Alpine flora, 

 which now descends on Kenya to the level of 10,400 feet, 

 must have been driven as far as the glaciers advanced. It 

 would thus have reached the contour line, which now stands 

 5000 feet above the sea. Other effects would have tended in 

 the same direction. The greater extent of the snowfields 

 must have increased the rainfall on the surrounding country. 

 Moreover, on the mountains there does not appear to be any 

 division of the year into wet and dry periods, as there is on 

 the plains ; the heavier rainfall would therefore have been all 

 the more effective, as it would have been distributed throughout 

 the year. The rainfall on the_ plains would also have been 

 increased in another way. In all mountainous countries, more 

 rain falls on one particular zone than either above or below it. 

 At present, in British East Africa, this " zone of maximum 

 rainfall" occurs between the levels of 7000 and 11,000 feet, 

 and thus only includes parts of the highest mountains, and not 

 the plains. But during the period of greater elevation of the 

 country, the maximum rainfall would have occurred at a 

 relatively lower level, and probably most of the surface of the 

 high plateaux was included in this zone. In much of the 

 country in which the rainfall is now scanty and uncertain, it 

 would therefore have been regular in distribution and con- 

 siderable in amount. 



The results on the vegetation of the district must have 

 been very great. The air being damper, it would no longer be 

 necessary for the plants to guard themselves against the drain 

 of moisture caused by the process of transpiration. The desert 

 scrub, which now covers the country, would have been replaced 

 by a less specialised and more normal type of vegetation ; the 



^ Quart. Joiirn. Geol. Soc. vol. 1. (1894), pp. 515-530. 



