xviii THE CRATERS OF THE RIFT VAELEY 227 



and Sii.swa ; and the Aberdare uioniitauis with the 

 high peak of Kinangop (13,214 ft.). 



Tlie Rift A^aJley ditiers from the common kind of 

 valley in the eharacter of its lateral boundaries. In 

 vallevs. as a rule, the sides slope gradually from the 



(jiunt Lobelias (L. Vcckeiiii). 



high ground to the low, Ijut in this ^-alley the sides 

 are, in places, as steep and abrupt as those of a grave : 

 indeed the traveller may suddenly come to the edge of 

 one of these steep walls and run a risk of tuml)ling over. 

 Steep boundaries of this kind are called " escarpments " ; 



