692 SYDNEY H. BALL AND MILLARD K. SEALER 



are usually well rounded; the larger are angular or only roughly 

 rounded; the medium-sized bowlders, those from 2 to 6 inches in 

 length, are three or four cornered and often striated. 



The striations are especially well seen on dense, close-textured 

 rocks, quartzite for example (Plate I). These can scarcely be 

 other than glacial striations. While through desert erosion some- 

 what similar scratches are produced, they are too abundant here 

 on a single bowlder, and the familiar tiny crescentric fractures 

 (nicks), caused by the striking of one bowlder by another in de- 

 scending the cloud-burst swept valleys of arid regions, are 

 absent. 



With but shght variations this description would answer for the 

 exposures on the Lualaba River at the Kitete Rapids where the 

 Lubilache is in contact with quartzite; at Bena Songo and Bena 

 MatabaH Rapids; at Plana Mulambo where the Lubilache lies on 

 slaty quartzite more or less folded; and at Mulambo Shamola. The 

 principal and most constant differences He in a shght variation in 

 the character of the matrix, which varies in color from whitish yellow 

 to greenish gray or dark gray, and in the degree of consolidation. 

 The matrix, which is usually incoherent, is well consolidated at Plana 

 Mulambo and Mulambo Shamola. At Bena Songo the irregular 

 distribution of the bowlders is well seen, many occurring for 100 

 feet laterally, and none in the next 100 feet. 



Where the underlying older rocks are exposed the bowlders 

 derived from them are more abundant and more angular than the 

 bowlders of other varieties. The bowlders and pebbles consist of 

 quartzite, of granites and gneisses, of limestones, etc. It is worthy 

 of note that at the most northerly of these outcrops of basal con- 

 glomerates at Mulambo Shamola, the larger pebbles are but six 

 inches in diameter. There are at all other localities great bowlders 

 two to three feet in diameter, of rocks not known to occur in the 

 immediate vicinity, that is, large bowlders which have been trans- 

 ported considerable distances. Typical examples of the contact 

 of these basal beds with the older rocks are seen in Fig. 3, A and B 

 representing respectively the contact with quartzite at the head of 

 the Kitete Rapids, and the contact with slaty quartzite at Plana 

 Mulambo. 



