While cutting a way through the bamboos we suddenly stumbled upon a block of lava (andesite). I was delighted to see it, for I had not previously seen as much as a pebble since we left Laikipia. As I examined it, my interest was roused.
The Great Rift Valley: Being the Narrative of a Journey to Mount Kenya and Lake Baringo with Some Account of the Geology, Natural History, Anthropology and Future Prospects of British East Africa, Psychology Press, 1968 , p. 158