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The Ndale volcanic field extends over an area of about 10x20 km (Geological Survey of Uganda 1:250,000 map 'Fort Portal'). The area is defined on the map as consisting of 'Volcanics: mainly tuffs with minor lavas': between 20 and 30 craters are indicated. Although an extensive field very little has been published on it. Holmes and Harwood (1932) describe a single specimen, which is a lithic tuff grading into agglomerate. This rock comprises fragments of basement rocks up to 2-3 cm across, lapilli of 'porphyritic melilite basalt' and isolated crystals, all cemented by calcite. The lapilli, which are as much as a centimetre in diameter, contain phenocrysts of olivine, biotite, melilite and rare aegirine-augite in a groundmass of opaque minerals, perovskite, augite and melilite in a brown glass. The term basalt is clearly inappropriate for this rock. It is likely that the rocks of this field are similar to those of Katwe-Kikorongo (No. 5) and Bunyaruguru (No. 6).
Fort Portal: 1:250,000 geological map, Geological Survey of Uganda, 1962. HOLMES, A. and HARWOOD, H.F. 1932. Petrology of the volcanic fields east and south-east of Ruwenzori, Uganda. Quarterly Journal of the Geological Society of London, 88: 370-442.