﻿644 MR. G. F. J. PREUMONT (W THE GEOLOGY OE THE [Aug. I905, 



III. Geology. 

 Ibembo — Buta. Lipodongu. Itembiri — Rubi Basin. 



On leaving Ibembo, to proceed up the Itembiri Eiver, towards 

 Buta, the first rocks encountered are at the rapid of Go, where the 

 river changes its name into Eubi. 



The Buta Shales. — Beyond the junction of the Likati Eiver 

 with the Eubi, appears a formation of laminated shales horizontally 

 stratified, and cropping out on the river-banks. They are in 

 appearance quite unmetamorphosed, and in places seem to pass into 

 sandstone. They continue to be seen along the banks of the Eubi, 

 right up to Buta. 



Close to Buta, and apparently intercalated in the Buta Shales, is 

 a small outcrop of oolitic limestone in irregular masses, many 

 cubic yards in size, which are buried in a light-coloured clay-soil,, 

 forming here the southern bank of the Eubi. The forest, hereabouts 

 very aense, prevents one from making a detailed investigation, 

 and no information could be gathered as to the relative position of 

 this outcrop with regard to the neighbouring shales. It looks like 

 a local occurrence of no great extent. All along the Eubi Eiver 

 the Buta Shales are most regular in appearance, and quite horizontal 

 in position. They do not seem to extend to any considerable distance 

 northward or eastward, as, in following up the course of the Eiver 

 Eubi (a road which we travelled on the return-journey) they are only 

 traced for about 20 miles farther east, a little before reaching the 

 Palls of Lipodongu on the Eubi, where granite appears. 



Northward we followed the Buta Shales up to the Bali Eiver, 

 about 12 miles north, where we noticed an outcrop of soft grey 

 sandstone, apparently running north-westward and south-eastward. 



Granite. — Between the Bali and Libokwa, and about 30 miles 

 north of Buta, a well-defined massive ridge of granite appears, 

 running in a north-westerly and south-easterly direction ; and the 

 intervening country is made up of alluvium and clay in the depres- 

 sions, while upon the slight eminences a limonitic puddingstone is 

 often met with. From Libokwa to Bima on the Uelle, the same 

 granite and ferruginous rocks are also abundant. 



The altitude of the Eubi basin at Buta is about 1600 feet above 

 sea-level, and that of the Uelle at Bima is about 2000 feet. Since 

 the distance between the two places does not exceed 55 miles in a 

 bee-line, the ascent is remarkable, and makes the basin of the Uelle 

 much higher than that of the Eubi. The separation of the two basins 

 is well-defined by this ridge of granite running westward close to 

 the Uelle. South-eastward this granite-ridge appears to extend 

 in the direction of the Lipodongu Falls on the Eubi. 



In entering the Uelle Basin, therefore, the main fact 

 to be noticed is its granitic substratum. 



