686 SYDNEY H. BALL AND MILLARD K. SEALER 



places, the summits of the greater elevations of this ancient sur- 

 face. While the contact is poorly exposed, the basal beds are 

 seen to be nowhere coarsely conglomeratic nor to contain many 

 pebbles. The well-rounded pebbles consist of quartz, chert, and 

 granite, all probably derived from the so-called pre-Cambrian 

 series. They are usually confined to the twenty feet immediately 

 above the contact, although in instances they occur considerably 

 higher. 



Between Luebo and Lusuna, where the base of the series is not 

 seen, conglomeratic beds or lenses were noted interbedded with 

 sandstone. In the Lualaba Valley within the zone of the Maniema 

 a basal conglomerate, which will be described later, is frequently 

 exposed in the valleys of the streams. 



The vertical range between the base and top of the Lubilache 

 is probably somewhat greater than 1,500 feet. At no one locality 

 however, known to the writers, is this entire thickness exposed. 

 In the upper Kasai region, between Luebo and Djoka Punda, 

 monadnocks, principally of massive red sandstone of this series, 

 rise 400 feet above the general plateau level, and 700 feet above 

 the river at the places named, thus exposing approximately 700 

 feet of this formation. 



In the Maniema the base of the series is considerably higher 

 than in the Kasai region, the base averaging 2,000 feet in the former 

 and 1,550 feet in the latter region. As the beds were deposited in 

 what appears to have been one and the same lake, this difference 

 in elevation is due probably to north-and-south faults parallel to 

 Tanganyika Lake. These successively have raised the country 

 from west to east upward. Evidence of this is seen in the isolated 

 outlier of sandstone in the Luiko Valley, later to be described (see 

 p. 691). 



Initial dips up to 5 or even 10 degrees were noted in the zone 

 of the Maniema, particularly where the sandstone occupies ancient 

 fjords extending up into the old mountains, and a slight initial 

 dip occurs away from the mountain masses toward the center of 

 the larger basins of deposition. For the most part, however, the 

 formation is essentially fiat-lying, and with few exceptions the dip 

 can be measured only in feet per mile and not in degrees. 



