﻿650 ME. G. F. J. PEEUMONT ON THE GEOLOGY OF THE [ Aug. I905, 



to be the simplest hypothesis that could suggest itself, from the 

 geological aspect of the country, but that as yet too little information 

 is available, and my observations are too incomplete, to advance 

 more precise conclusions. 



No fossils have been found in these limonitic conglomerates, so far 

 as I am aware. 



A practical aspect of their occurrence is that they constitute an 

 excellent material, always ready to hand, for the making of hard 

 roads. This should be of importance to the Congo State Govern- 

 ment, who are, I believe, now engaged in constructing such roads. 



The superficial limonitic formation described is not exclusively 

 confined to the Uelle district, and similar rocks are found in many 

 parts of Africa, on the western coast, and in most districts of the 

 Congo. Referring to the Katanga, and quoting the eminent 

 authority of Dr. E. Dupont in support, the learned geologist Cornet 

 describes it as follows T : — 



1 These deposits are generally of a yellowish-red or brick colour, due to a 

 large proportion of hydrated oxide of iron. It is this hydrated oxide of iron 

 which, in concreting in the mass of the material, principally near the base, 

 gives rise to beds, lumps, or nodules often embedding rolled pebbles in a sort 

 of impure limonite of cellulous and scoriaceous aspect. The proportion of 

 iron contained is often sufficient to allow of its being used as iron- ore by the 

 natives. Where the superficial action of water has taken off the soft parts 

 of the deposit, the scoriaceous limonite appears in isolated blocks on the 

 surface, or constituting floors often of considerable extent. . . . This scoria'ceous 

 limonite is more especially found where the subsoil is made up of practically- 

 impermeable rocks.' 



Dr. Cornet gives the name of ' red deposit ' to this formation in 

 the Congo, and remarks, very justly, that its only point of resem- 

 blance to typical laterite lies in the possession of a brick-red colour. 



Arebi — Mount G-aima. 



The south-eastern portion of the district, comprised between the 

 Uelle-Kibali and the Bomokandi Rivers, forms a hilly and even 

 mountainous country with Arebi for a centre, averaging in altitude 

 nearly 3000 feet. At the headwaters of the Uelle-Kibali, near 

 Lake Albert and the Mle Territories, the ground is still higher, 

 and there probably exceeds 3600 feet in average altitude. This 

 hilly zone appears to be entirely granitic in nature, and some 

 prominent mountains, such, for instance, as Mount Tiberi (4210 

 feet above sea-level), are solid masses of granite. The whole extent 

 of country west of Arebi towards Gumbari, and north towards 

 Mount Combe, is granitic. Nearer Arebi, a little farther north, 

 rocks more basic in appearance are occasionally met with. At the 

 junction of the Motu and Arebi rivers a phyllite was observed, 

 in a small outcrop striking north-north-west and south-south-east, 

 with an easterly dip. 



1 Ann. Soc. geol. de Belg. vol. xxi (1892-94) Mem. pp. 230 & 231. 



