﻿Vol. 6 1.] PETROLOGY OF ROCKS PROM THE CONGO FREE STATE. 655 



In the Nile Territory the rocks are all more or less metamorphic, 

 but the country shows here and there peaks of granite (such as 

 Mount Loka, the Dinkala Hills, and Kodjokadji) piercing through 

 the stratified series of gneiss, quartzites, and mica-schists. 



Recent eruptive rocks are comparatively rare, such being found 

 only at Redjaf. These are dykes of basic andesitic rock, which 

 intersect the gneissose series. 



Similarly to the greater part of Equatorial Africa, this area 

 appears to be devoid of fossils, although it is possible that further 

 and more competent search may yet reveal some. 



It will be seen that the foregoing observations tend to confirm 

 the views already held as to the geological features of this portion 

 of the Congo Basin ; the granitic and metamorphic primary rocks 

 are present across the whole country from east to west and from 

 north to south, uncovered by any other rocks except the alluvial 

 clays and sands and the nearly-related ferruginous rocks ; the grey 

 and red sandstones, so prominent in the regions lying west, south, 

 and east of the Uelle Basin, are conspicuously absent. 



V. Petrological Notes. By J. Allen Howe, B.Sc, F.G.S. 



Rocks from the Neighbourhood of Buta. 



Specimen No. 48. 1 — This is a fine-grained, chocolate-coloured, 

 laminated mudstone containing minute flakes of mica. There is no 

 trace of any fossil, unless one or two microscopic pellets may be 

 taken to represent coprolites. 



No. 42, Rubi River. — From large blocks apparently embedded in 

 the clayey alluvium of the river. 



It is a compact cream-coloured rock, with well-marked oolitic 

 structure. In the thin slice, opaque, dull, spherical grains are seen 

 in a fairly-large amount of granular crystalline calcite, which forms 

 the matrix. The grains are fairly uniform in size, and all possess a 

 well-defiued concentric structure ; there is no trace of any radial 

 structure, and the material is too dusty in character to give a cross 

 in polarized light. The centres of the grains are usually filled with 

 more or less clear granular calcite, and no organic or clastic bodies 

 have been noticed in them. There are several compound grains, 

 one large grain enclosing one or two smaller ones. (See PI. XLIV, 

 fig. 2.) 



The rock is suggestive of an oolite formed from a calcareous 

 spring, but there is nothing to show that organisms have taken any 

 part in its formation. In places the rock includes small pellets of 

 grey clay [52], and where this is present the limestone tends to 

 assume a stylolitic structure. 



1 These numerals refer to the microscope-slides and rocks deposited in the 

 Museum of Practical Geology, Jermyn Street, London. 



