He visited central Kenya in 1893 and again in 1919 and his 1896 book The Great Rift Valley is considered a classic.John Walter Gregory (Wikipedia)
John Walter Gregory, FRS, FRSE, FGS (27 January 1864 – 2 June 1932) was a British geologist and explorer, known principally for his work on glacial geology and on the geography and geology of Australia and East Africa.The Gregory Rift in the Great Rift Valley is named in his honour.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.
John Walter Gregory, The Great Rift Valley