XVIII THE CRATERS OF THE RIFT VALLEY 235 
because lions were known to lurk about the long grass, 
and he thought it advisable to reach Nakuru before the 
sun went down. 
It interested me very much to find craters existing in 
the Rift Valley with their sides clothed with tall grass, 
the floor of the crater occupied with a forest, and the 
whole basin large enough to afford food and shelter for 
herds of wild animals, some of them—rhinoceros and 
elephant—being the biggest mammals living on this 
planet to-day. 
The most common fate of the crater of an extinct 
volcano in Europe is to become a receptacle for water. 
Two of the best examples are Lakes Albano and Nemi 
near Rome. It is, however, historical that toward the 
end of the seventeenth century the crater walls of 
Vesuvius were hung with trees and brushwood; its floor 
was a grassy plain on which cattle grazed and the wild 
boar lurked in the thickets. 
Mount Elgon is an extinct volcano with a base forty 
miles in diameter. The greatest altitude at the rim is 
14,200 feet. The crater, eight miles in diameter, is 
crossed by a native track from north to south. Snow 
falls on the highest points of this mountain, but does 
not lie long. Joseph Thomson discovered this mountain 
in 1883 and described it as an outpost of the great 
central lava-field of Masailand. This explorer also 
reached the remarkable caves on the southern slope 
which have puzzled everyone who has visited them since 
his day. The upper slopes of Elgon are clothed with 
dense forests formed in part of bamboos : the lower 
slopes are very fertile and bananas grow abundantly. 
There are no active volcanic signs at the southern 
extremity of the Rift Valley ; near the equatorial section 
of this meridional trench there are a few indications in 
the shape of steam-vents and hot springs. There is a 
steam-veut on Longonot, and some very active jets on 
Donyo Burn, and one is reported on Menengai. There are 
hot springs at the southern end of Baringo, also sulphur 
