A CENTRAL AFRICAN GLACIER OF TRIASSIC AGE 685 

 LUBILACHE FORMATION 



The Lubilache formation, in which the glacial features occur, 

 was first described by Dupont^ and named by Cornet^ from the 

 Lubilache (Sankuru) River, where it is typically developed. It is 

 the essentially flat-lying sandstone-shale series which covers the 

 central Congo basin, not rarely extends in tongues into the rim 

 plateau and mountain regions, and at several points crosses beyond 

 the Congo basin. In general this series is made up of sandstones 

 and shales in alternating beds, which grade into one another both 

 laterally and vertically. 



As a rule massive bedding predominates in the sandstones 

 as does a reddish color; grayish and white beds are, however, not 

 uncommon. 



In the lower Kasai region particularly, a quartzitic phase is 

 often developed in the sandstones by the deposition of secondary 

 silica by surface waters. In extreme instances this action results 

 in a rock almost cherty in character, which is often cellular, the 

 weathered surface being pitted. In the upper Kasai and Sankuru 

 regions this quartzitic phase is rare, the sandstones being medium 

 grained and having usually a saccharoidal texture. In the Lualaba 

 (Upper Congo) area hard, fine-grained maroon sandstones cemented 

 with a ferruginous pigment predominate. In all cases the sand- 

 stones are typically quartzose, although near the base of the forma- 

 tion at many places, feldspathic material is present. 



The shales are usually fissile and vary in color from greenish 

 gray to tan and drab. 



In the vicinity of Nyangwe, on the Lualaba River (Upper 

 Congo), shales, well exposed, are more or less bituminous, but 

 grade laterally both up and down the river into more arenaceous 

 beds. West of Kasongo, toward Lusunu, these beds are almost 

 sandstones. 



The basal beds of the formation are generally slightly con- 

 glomeratic. In the vicinity of the junction of the Lulua and Kasai 

 rivers the ancient erosional surface upon which the flat-lying 

 sandstones and shales were deposited undulated very gently. 

 The down-cutting of the stream valleys has exposed, at numerous 



' Dupont, op. cit. ^ Cornet, op. ciL, XXI, 211. 



