The Charnockite Series of Uganda, British East Africa

Abstract

I. Introduction Though Sir Thomas Holland (1900, p. 131) counselled that the designation “charnockite series” should not be applied to apparently similar rocks outside India unless their genetic relationship with the type series could be proved, the striking parallelism between that series and the rocks to be described in this paper appears to justify reference to the latter as “the Uganda chamockite series”. The Uganda series comprises four main divisions—acid, intermediate, basic, and ultra-basic—and includes nearly all the types known in India. In Uganda, as in India, the sub-acid to basic types predominate. Hypersthene-bearing rocks were discovered at several localities in Bunyoro by E. J. Wayland and W. C. Simmons, and subsequently in Karamoja by Wayland and in the West Nile District by Simmons. A few of these rocks were provisionally identified in the field as “charnockites”, but the existence of a series of rock types akin to the charnockite series of India was not established until 1931, when I was able to make a complete petrological study of the collections. Hypersthene-bearing rocks were then found to be more abundant and more widely distributed than had hitherto been suspected, their occurrence being discovered in many new localities in each of the three main areas just mentioned. The present paper is based on a study of 110 specimens of the charnockite series, 10 representative rock analyses, nine analyses of minerals, and a large number of specimens of country rocks. II. Distribution and Mode of Occurrence The outcrops of the charnockite series