Tinderet is a large volcano which is centred in the northern part of the Kericho area (No. 085-00-046) but extends northwards into the Kapsabet Plateau area (No. 085-00-030) and eastwards into the Molo area (No. 085-00-049). The eastern part of Tinderet is intercalated with the products of the Londiani volcano, which commenced eruption before cessation of activity at Tinderet (Binge, 1962). The complex has an east-west diameter of some 50 km and Tinderet rises to over 2,800 m, about 800 m above the surrounding country. Volcanic activity commenced with eruption of tuffs which pass upwards into at least 300 m of agglomerates composed mainly of nephelinite and melanephelinite (King et al., 1972). Plateau phonolites originating in the Mau area then flowed around the ash cone. A more intense phase of activity then commenced at Tinderet with the production of coarse nephelinitic agglomerates. Subsequently phonolitic nephelinite lavas were erupted from the Londiani centre, and these flowed westwards to overlie the Tinderet agglomerates. Activity continued with the production of further phonolite and melanephelinite and ended at Tinderet with eruption of analcime basanite and tephrite flows that cover most of the mountain with a distinctive feldsparphyric variety capping the summit area. Later Londiani phonolites infilled valleys eroded into Tinderet. The melanephelinites have pyroxene in excess of nepheline and amongst this group are melilite-melanephelinites and melilitites. According to Binge (1962) the melilite-rich rocks generally occur on the summits of small cone-shaped hills and may be intrusive. In some rocks the melilite is confined to the groundmass but in others it forms phenocrysts up to 2.5 mm long. The nephelinites contain phenocrysts of nepheline and aegirine-augite, rimmed by aegirine, with accessories including perovskite and, in some rocks, melanite. They grade into phonolitic nephelinites in which feldspar is present in the groundmass. The basanites contain olivine and augite phenocrysts and a groundmass characterised by the presence of analcime, while the tephrites are distinguished by greater abundance of analcime in the groundmass together with oligoclase, biotite, apatite and katophorite. A range of whole rock analyses are given by Binge (1962).Le Bas and Dixon (1965) first recognised that the limestone being quarried at Koru is carbonatite and subsequently Deans and Roberts (1984) demonstrated that the fossiliferous Koru limestones occurring around the northwestern and southwestern flanks of Tinderet are all carbonatitic. They describe in some detail three localities i.e. the Koru (Legetet), Songhor and Kipsesin-Ngeron areas, all of which include a range of carbonatite tuff, some water lain, and agglomerate horizons. All these rocks contain at least 50%, by volume, of primary carbonate and generally >90%. Clasts consist of carbonatite lava, sovite and alvikite together with crystals of apatite, magnetite, biotite and titanian garnet. Numerous textural variants of the carbonatitic rocks are illustrated by Deans and Roberts (1984) and certain rectangular pseudomorphs of calcite are interpreted by them as being after nyereite; however, this interpretation is not now generally accepted; they are usually considered to represent primary calcite phenocrysts. The carbonatite intrusion of Buru Hill near Tinderet is described separately (No. 085-00-048).