84 Problems of Economic Biology in East Africa 



to Kilimanjaro in the soutli. This is the shorter arm of the Great Rift ; 

 the other, and longer, passes to the westward and embraces lakes Tan- 

 ganyika and Nyassa. 



The Uganda Railway crosses the Rift Valley at an angle and at the 

 point where it crosses the two escarpments, the western or Mau escarp- 

 ment is slightly higher (8320 feet) than the eastern or Kikuyu escarpment 

 which is just under 8000 feet (see vertical diagram). Along the western 

 rim of the escarpment between latitude and 1 S. lies the Aberdare range 

 which runs for a distance of 30 miles due north and south, and attains 

 a height of 13,000 feet. The average height of the two escarpments is 

 between 2000 and 3000 feet above the floor of the valley, itself some 

 6000 to 7000 feet above sea level, where it is crossed by the railway. The 

 drop is always steep and in some places almost precipitous. It will be 

 seen from the diagram that the land rises rapidly from the coast and that 



Ml 



580 500 400 300 200 100 



550 450 350 250 150 50 



Fig. 1. Vertical diagram of Uganda Railway. 



a comparatively short distance along the railway in the direction of 

 Victoria Nyanza the altitude increases very considerably. The meteoro- 

 logical conditions along the course of the railway are very varied. Thus 

 at Mombasa the annual rainfall is between 60 and 70 inches, but 60 miles 

 inland, at Mackinnon Road Station (1300 feet) the average fall is not 

 much more than 10 inches. Again Nairobi (5500 feet) has an annual 

 rainfall of 30 inches, but 25 miles farther along the line Limuru (7500 feet) 

 records an average rainfall of 70 inches. The different climatic conditions 

 at these two places as a result of altitude are remarkable and exert a 

 marked influence upon the spread of fungous diseases. 



It is proposed to discuss shortly the most important problems of the 



