﻿Vol. 6 I.] ON ROCKS FROM THE CONGO FREE STATE. 663 



and in relation to the surrounding rocks, but as it was found in 

 an isolated lump, it is not safe to do more than mention the occur- 

 rence. No fossils have been seen in the thin section of this rock. 



Summary. 



The results of the examination of the rocks from the Uelle Basin 

 and the Lado Enclave may be briefly summarized as follows : — 

 In the extreme western part of the region, about Buta on the River 

 Rubi, are the only ' post-primary ' rocks — to use Cornet's expression 

 - — observed in the whole region ; that is, if we leave out of account 

 the chert in loose blocks found near Suronga. Nothing else has 

 been seen that would represent the Kundulungu Beds of Cornet or 

 the Karagwe Series of the East- African Lake-District. 



Prom Djabbir and the Lipodongu Falls on the Rubi River, as far 

 as Bomokandi and Poko, if not somewhat farther, granite of fairly- 

 normal type predominates. 



Farther east, mica-schists and quartzites set in, and include 

 the remarkable iron-mountains of the central area — comprising 

 the mountains of Angba, Mandjana, and Madjema, and the groups 

 about Mount Tena and Mount Gaima. 



In the south-eastern corner of the region examined, about the head- 

 waters of the Bomokandi and Uelle-Kibali Rivers, there appears to 

 be a complex massif ofdiabasic rock in various stages of freshness 

 or of extreme crushing, along with microcline-granite-gneisses 

 and chloritic phyllites. 



Northward, along the boundary of the Congo State and the Bahr- 

 el-Ghazal, a series of very coarse gneisses occurs (pegmatoid 

 gneiss), with large mica-, felspar-, and quartz-elements and local 

 developments rich in tourmaline, kyanite, and garnet. 



From the Nile about Dufile, down the river as far as Lado, 

 quartz-schists, mica-schists, and microcline-gneiss are 

 the only rocks collected, with the two exceptions of the basic 

 andesite from the dykes south of Redjaf, and an amphibolite 

 from a point midway between Loka and Kodjokadji. 



No attempt has been made in these notes to correlate the rocks 

 with others from surrounding regions, as the necessary imperfections 

 of the field-evidence prevent any such effort from being of much 

 value ; we have, therefore, been contented to place on record a few 

 isolated facts, in the hope that they may be of use to future workers 

 in this area. It may be pointed out, however, that the crystalline 

 rocks of the eastern portion of the area described appear to be 

 analogous in every way to the rocks of the same age in Uganda, 

 British East Africa. 



Special references were not needed, as there has hitherto been no 

 more than a brief mention of the geology of the greater part of 

 the district here described, but we append a short list of papers 

 dealing more or less directly with the neighbouring areas. 



