682 SYDNEY H. BALL AND MILLARD K. SHALER 



square miles, or greater than that of all the United States east of 

 the Mississippi River. 



The zone of the Maniema is situated in the Upper Congo region, 

 and includes that part of the Lualaba (Congo) Valley between 

 latitudes 3 and 5 degrees south. The principal state post in the 

 zone is Kasongo (Fig. i). 



TOPOGEAPHY AND DEAINAGE 



From north to south, Africa is made up of three topographic 

 elements: the Atlas Mountains, a highly accentuated region of 

 closely folded rock; the Soudan and Sahara desert region, a more 

 or less accidented plain in which the rocks are, in the main, flat- 

 lying; and the central and southern tablelands with the Abyssinian 

 plateau, consisting of intensely folded older, and horizontal younger 

 rocks. 



The Belgian Congo lies within the plateau region, and consists 

 from west to east of: (i) a narrow coastal plain, which faces the 

 Atlantic Ocean, rising to (2) an ancient mountain range, now eroded 

 to an intensely dissected plateau, and frequently referred to as the 

 Crystal Mountains (the higher domes reach an altitude of 2,300 

 feet; through the hard rocks of this plateau the mighty Congo 

 rushes in a series of rapids, and low waterfalls, the non-navigable 

 stretch between the Lower and Upper Congo rivers) ; (3) the great 

 interior region, a basin whose slopes rise gently from Lake Leopold 

 II (altitude 1,110 feet). The limits of the basin to the north 

 (altitudes from 2,500 to 4,200 feet) and to the south (from 4,000 

 to 5,000 feet) are comparatively low, but to the east rise the Eastern 

 Frontier Mountains, in height averaging about one mile above sea- 

 level. Certain peaks like the volcanic Ruwenzori (altitude 16,800 

 feet) rise to altitudes exceeding 15,000. These mountains are in 

 part due to folding, but largely to north-and-south faulting with 

 which are genetically connected important volcanic phenomena. 



The Congo River and its tributaries drain the Belgian Congo 

 with the exception of a small area in the extreme northeastern 

 part, the waters of which find their way into the Nile. The princi- 

 pal affluents of the Congo are the Kasai, Sankuru, and Ubangi. 

 It is 4,640 kilometers in length, and the sixth longest river in the 

 world. 



