A CENTRAL AFRICAN GLACIER OF TRIASSIC AGE 695 



The laminae of the shale are concentric with the form of the 

 bowlders, being slightly arched over, and greatly bowed under 

 them, as if they had been dropped from considerable heights into a 

 plastic mass. 



Within the limits defined these bowlders occur at numerous 

 localities, as shown in Fig. 2, at stratigraphic positions from 0-200 

 feet above the base of the formation. Two exceptions should be 

 noted: At Bena Tomba, latitude 4° 30' S., on the bank of the 

 Lufubu River, and at Tubila on the Lualaba, latitude 1° 30' S., 

 bowlders of older rocks lie upon the surface. The underlying 

 rock is the Lubilache shale. The source of these bowlders is not 

 known; they may have weathered from the shale, or they may have 

 been carried to the points named by the natives, by whom such 

 hard rocks are used in grinding foodstuffs. 



The largest bowlder noted is of granite and was found by Smith, 

 about one mile north of the Luila River. This bowlder measured 

 5X3X3^ feet. Numerous other large bowlders were noted in the 

 shale northeast of Kasongo. 



From the fineness of the inclosing shale, the size of these bowlders, 

 and their great distance in many cases from their source, it is 

 evident that they were dropped from some object floating on the 

 surface of the body of water in which the Lubilache was deposited. 

 They could have been transported in but one of two ways: (i) 

 by being imbedded in the roots of floating trees, or (2) by being 

 carried by icebergs. 



That bowlders of such enormous weight could be transported in 

 the roots of floating trees is improbable. Furthermore, the shales 

 of the Lubilache are practically barren of vegetable remains, par- 

 ticularly fossil tree trunks; absolutely none of the latter having been 

 noted. The bowlders are numerous along the Lualaba and are 

 known nowhere else in the formation. It is scarcely conceivable 

 that the shores of this portion of the basin of deposition were alone 

 bordered by trees capable, when swept into the lake, of trans- 

 porting bowlders of several tons weight in their roots. Moreover, 

 fragments imbedded in tree roots are usually not only angular 

 or subangular, but also small and of weathered rock; while in all 

 cases the erratic bowlders of the Lubilache shale are rounded or 



