I Introduction. Mount Kenya, the greatest mountain in British East Africa, was discovered by Ludwig Krapf, 2 when on December 3rd, 1849, he saw its two-horned summit from a hill above the Wakamba village of Kitui. No suggestion as to the structure of Kenya was made until 1883, when Joseph Thomson, after a view of the mountain across the Laikipia plateau, described it as the denuded remnant of an old volcano. ‘The peak,’ he tells us, ‘without a doubt represents the column of lava which closed the volcanic life of the mountain . . . . The crater has been gradually washed away.’ The first definite geological information about Kenya we owe to Count S. Teleki, who was the first European to reach the mountain; in 1887 he climbed the western slopes to the height, of about 13,800 feet, and brought back some rock-specimens which have been described in detail in a valuable memoir by A. Rosiwal. This petrologist determined the specimens as augite-andesite, andesitepitehstone (hyalo-andesite), and phonolite, and thus proved the volcanic nature of the mountain. Teleki's account of the structure of Mount Kenya differed, however, from that of !Fnomson. The former climbed through the forest-belt from Ndoro and entered a valley, which I have named the Teleki Valley (see map, P1. X); he followed this eastward until it suddenly bent northward and expanded into two great glacier-filled valleys, on the southern and south-western sides of the central peak. The high western wall of the Tyndall Glacier, the main