XVIII THE CRATERS OE THE RIFT VALLEY 227 
and Suswa ; and the Aberdare mountains with the 
high peak of Kinangop (13,214 ft.). 
The Rift Valley differs from the common kind of 
valley in the character of its lateral boundaries. In 
valleys, as a rule, tlie sides slope gradually from the 
(Uant Lobelias [L. Deckenii). 
high ground to the low, Imt in this valley 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 tumbling over. 
Steep boundaries of this kind are called “ escarpments ” ; 
Q 2 
