Petrology of the Volcanic Fields East and South-East of Ruwenzori, Uganda

Abstract

I. G eneral D escription of the V olcanic A reas U ntil 1891 the possibility was entertained that Ruwenzori, like the other high mountains of Central Africa, might be of volcanic origin. As a result of his explorations during that year, Dr. F. Stuhlmann (1894) showed that this preliminary suggestion was without foundation, adding that no signs of volcanic activity had been detected in the regions traversed. In 1894, however, G. F. Scott Elliot recognized three well-marked volcanic belts in the adjoining country east and southeast of Ruwenzori ( Elliot & Gregory, 1895, p. 674 ; Elliot, 1896, p. 168 ). He described the bedded tuffs, craters, and crater-lakes of Toro (fig. 1) as occurring in the Vijonga area (Lake Kijongo), north-west of Fort Portal; the Butanuka or Kyatwa area, south of Fort Portal, locally forming the boundary of the low Toro plains to the east; and the Katwe and Kaihura Straits area (north-west of the Kazinga Channel between Lakes George and Edward). It is remarkable that Stanley failed to recognize the volcanic origin of the famous salt-lake of the Katwe crater. He visited the locality in 1889 and commented on the deep depression and the salinity of the lake, and even recorded the occurrence of a spring of sulphurous water. Scott Elliot also indicated that Karimi Hill, south-west of Ruwenzori (now in Belgian territory), might be of volcanic origin, and suggested that the different belts of cones and craters were alined on fissures radiating outwards from the uplifted massif of Ruwenzori. The nature of Karimi Hill