The northern half of the Kericho area (Binge, 1962) is dominated by the Tinderet volcano, which is described separately (No. 085-00-047), while the southern part and most of the Sotik district (Schoeman, 1949) to the south are covered by plateau phonolites with lesser areas of tuff and nephelinite. The sources of the plateau lavas lie to the west in the Molo (No. 085-00-049) and Mau (No. 085-00-050) areas but the source of the earliest volcanic rocks, a sequence of tuffs, is not clear. The phonolites of the Sotik area were not subdivided by Schoeman (1949) whereas Binge (1962) distinguished, excluding rocks of the Tinderet centre, Kericho phonolites, phonolites of Kenya type, trachytoid phonolites and a large area of phonolitic nephelinites. The phonolitic nephelinites are defined as having a nepheline:orthoclase ratio exceeding 2:1 and, compared with the phonolites, they contain more nepheline phenocrysts while phenocrysts of aegirine-augite and titanite are present; katophorite and aenigmatite are sparse. The phonolites also contain alkali feldspar and nepheline phenocrysts and katophorite and aenigmatite are abundant, the latter sometimes being dominant; pyroxene, biotite and olivine are rare constituents. Binge (1962) gives whole rock analyses of a range of lavas.
BINGE, F.W. 1962. Geology of the Kericho area. Report, Geological Survey of Kenya, 50: 1-67.SCHOEMAN, J.J. 1949. Geology of the Sotik area. Report, Geological Survey of Kenya, 16: 1-39.