Kadam

The Kadam volcano has a diameter of some 35-40 km but its southern margin is not clear because of interdigitation with products of Mount Elgon (No. 24). The positions of the principal vents are not now apparent but radial dips of agglomerates near Obda, the present summit, and at a subsidiary summit Tebtho to the northeast suggest probable locations. Three quarters of the volcano is built of agglomerates which are essentially uniform throughout, and consist of blocks, up to many metres in diameter, in a matrix of smaller fragments and ash. The blocks are essentially of nephelinite and melanephelinite, but there are occasional angular fragments of basement gneiss. The igneous fragments consist of pyroxene and nepheline phenocrysts in a matrix of the same minerals, the proportions being generally about equal. Magnetite is abundant and titanite common while a green amphibole takes the place of pyroxene in some rocks. Phonolite blocks are not uncommon and are similar to the nephelinites but for the presence of twinned laths of orthoclase. Melilite occurs in some nephelinites. Tuffs are also present and the presence of fossil wood in some of them is taken by Trendall (1961) to indicate deposition in water. As well as pyroxene, nepheline and amphibole crystals the tuffs also contain quartz and microcline fragments that probably derive from the basement. Lava flows make up about one quarter of the volcano and may be up to 30 m thick. Most of the flows are nephelinite and melanephelinite of similar petrography to the agglomerates, with rather fewer of phonolite and melilite and olivine nephelinites. Dykes and plugs of the same rock types as the volcanic rocks occur throughout the volcanic succession. Dykes, sills and small irregular intrusions are distributed around the volcano, particularly to the north and east. The majority are of nephelinite but tinguaite and one dyke of basalt have also been mapped (Trendall, 1961).