486 
THE GEOLOGICAL HISTORY 
the Miocene. Otherwise, if we accept the conclusions that 
the augite andesite of Kikongo is a very ancient lava, which has 
nothing to do with the modern volcanic series, and that the 
phonolites of Lumbwa are of the same age as those of the 
Kapiti and Athi Plains, all the phonolites in the country were 
discharged after the Miocene. The whole volcanic history of 
British East Africa w T ould then be confined to the post-Miocene, 
and the oldest of the volcanoes would be Pliocene. It seems 
to me impossible that the whole volcanic history of British 
East Africa can be restricted within so short a time. 
The evidence of Mount Kenya is illuminating in this respect : 
Kenya is an old volcano in a very advanced stage of decay. 
Its peak appears from a distance as a mere rock pinnacle on 
the summit of a vast mound. Teleki, impressed by the curved, 
smoothed form of the valley subsequently named after him, 
regarded that as the extinct crater. But the crater of Kenya 
was long since destroyed. The mountain was at least 8000 
feet higher than it is now, and as it was worn down the crater 
was swept away. 
The peak is the plug of lava which solidified below the floor 
of the crater and choked up the throat of the volcano. 
The weathering of the volcanic rocks around the plug has 
produced two different types of rock scenery : there are rough 
crags and pinnacles due to ordinary subaerial denudation ; 
there are# smooth, rounded rock surfaces and blunted 
summits due to the abrading action of glaciers. The glaciers 
of Kenya were once more extensive, and flowed down the 
mountain for several thousand feet below their present level. 
The contrast between the jagged rocks, due to ordinary 
denudation, and the smooth slopes worn by the glaciers, are 
well shown in the beautiful photographs of Kenya by the 
Hon. Wm. MacGregor Ross, Dr. J. W. Arthur, and Dr. J. D. 
Melhuish. (Photographs, Figs. 2 and 8.) 
These glaciated surfaces show that the valleys had been 
cut down to their present depths at the time of the maximum 
extension of the glaciers. Not only had its eruptions ceased 
long before the formation of the volcanoes with well preserved 
craters — such as the Kibo summit of Mount Kilima Njaro, 
Longonot, Suswa or Meningai ; but Kenya had been reduced 
