The Molo area lies on the western shoulder of the rift and is entirely covered by volcanic rocks together with lacustrine and fluviatile sediments derived from them (Jennings, 1971). The bulk of the volcanic rocks are pyroclastics, originating from several sources, with lavas less common but morphologically prominent. Lavas include phonolite, nephelinite, basalt, trachyte and quartz trachyte with the most undersaturated rocks being concentrated in the west of the area about the Londiani volcano, which is continuous with the Tinderet centre (No. 085-00-047). The oldest lavas are phonolites of Miocene age, which correlate with the Kericho phonolites of the Kericho area to the west (No. 085-00-046), and within which some olivine basalts are intercalated. The phonolite is characterised by phenocrysts of nepheline, feldspar and biotite with resorbed microphenocrysts of aegirine-augite fringed by aegirine set in a groundmass of feldspar, sodic amphibole and aenigmatite. The nephelinites range from phonolitic nephelinite containing feldspar phenocrysts through nephelinite, varieties of which contain minor melilite and perovskite, to olivine melanephelinite. Some of the quartz trachytes contain sodic amphibole and generally aenigmatite. Most of the tuffs of the Molo area are of ash-flow type (Jennings, 1971) with some welded units; they are generally trachytic or phonolitic in composition. Many individual units have been mapped by Jennings (1971) to whom reference should be made for further details.