438 
THE GEOLOGICAL HISTORY 
vast plateau eruptions, which gave rise to the Lumbwa phono- 
lites and the later basalts. Fresh faults widened the Rift 
Valley, and these movements led to the building up of great 
trachyte mountains in the floor of the Rift Valley, including 
Lorgasailik, Suswa, Longonot, and Meningai. Some of these 
latest eruptions must have been quite modern. It is difficult 
to regard, for example, the north-eastern lava flow of Meningai 
as having been discharged more than a couple of centuries ago. 
Mr. Hobley regards the bare volcano that he discovered to 
the west of the Njorowa Gorge as not more than a century old. 
There are traditions among the natives of eruptions in modern 
times ; thus the formation of the Simbi Crater is said to have 
happened eighty years ago. Mrs. Ulyett, of Makalia, tells 
me that, according to a native once employed there, the 
mountains discharged fire a few generations back. The Masai 
appear to have no traditions of eruptions ; but they are 
nomads and pastoralists, and would have had no shambas 
devastated and homes destroyed, so negative evidence in 
their case is of little weight. 
The conclusion that Kenya was dead and dissected before 
the beginning of the Pleistocene, is based on the natural as- 
sumption that the former greater size of the Kenyan glaciers 
was during ‘ the Great Ice Age ’ in Europe ; for at that period 
the rain-carrying cyclones, which normally cross southern 
Europe and the Mediterranean, would have been deflected to 
a more southerly route by the anticyclonic conditions then 
dominant over north-western Europe. 
Kenya, probably, then had a heavier snowfall as its share 
of the increased precipitation over northern Africa ; and after 
the disappearance of the glaciers from north-western Europe 
they dwindled on Kenya as part of that widespread desiccation 
of northern Africa, which led to the gradual reduction in the 
size of the lakes and the disappearance of Lake Suess from the 
basin south of Longonot. 
The history of the East African lakes shows that the earlier 
stages of the volcanic activity in East Africa were passed 
through a long time ago. The surface of Lake Naivasha stood 
150 feet above its present level when it overflowed southward 
down the Njorowa Gorge. The entrance of the gorge (Fig. 4) 
