— 17 — 
reached its most westerly position and from there turns northwards 
along the Marrah hills in Darfur, dividing the scanty waters of the 
Bahr-el-Arab and its tributaries from the rivers draining into Lake 
Chad. From the Marrah hills the watershed travels in a north-easterly 
direction to a point close to the Nile on the 20th parallel of latitude near 
Hannek. 
Of the lands enclosed within this watershed, all that are drained 
directly into the Main Nile are desert. There are occasional showers, 
and some of the valleys and ravines carry water for a few hours every 
year, others every second, third or fourth year, but they contribute 
practically nothing to the volume of the Nile. The rains generally 
come in the winter when the Nile is falling every day, and the steady 
fall of the Nile is never arrested by the waters of any or all of these 
watercourses. The country west of the White Nile past Kordofan and 
Darfur to the Marrah hills is steppe land producing scanty grasses and 
forests of low accacias in the south, and rising to a general height 
of about 600 metres at the Marrah hills. The lands drained by the 
Gazelle river and the Albert Nile north of Gondokoro are flat plains or 
swamps in the north and east, and wooded and broken ground in the 
west and south-west, where the tributaries of the Gazelle river rise in 
the Blue mountains at a general height of 1500 metres. The upper 
waters of the Sobat and its tributaries drain the well wooded and culti- 
vated mountain masses of Gallaland and then traverse the marshes and 
flat lands which lie east of the Sudd region. The Blue Nile and its upper 
tributaries drain the choicest portions of the high Abyssinian mountain 
plateau lying over 2000 metres above sea level, and rising in places 
to 2500 metres and upwards. The lower courses of the Blue Nile, 
the Rahad and the Dinder are through the black cotton soil plains of 
the eastern Sudan, which are either wooded or covered with dense grass 
in the south. The Atbara and its tributaries in their upper courses 
drain the northern slopes of the Abyssinian plateau, and traverse the 
level plains of the eastern Sudan in a direction parallel to the Blue 
Nile. 
The Albert Nile and its tributaries between Gondokoro and Lake 
Albert traverse the broken and hilly country which is cut through by 
the Albert Nile at the Fola and succeeding rapids. The catchment 
basins of Lakes Victoria and Albert are the undulating hills, the flat 
marshy valleys, the great lakes and, in parts, high hills which constitute 
2 
