610 THE FRESH- WATER LOCHS OF SCOTLAND 
sheet of water of irregular outline, with low marshy shores, ranging 
in depth from 13 to 30 feet. It extends about 50 miles in an 
east-and-west direction, and towards the eastern end breaks up 
into several long arms which receive the waters of other lakes 
lying on the plain west of Mount Elgon. Two of these, Lake 
Salisbury and Lake Gedge, form one sheet in rainy weather. The 
River Mpologomia, which flows into Lake Choga, and is one mass 
of papyrus at its entrance to the lake, has been described as a 
backwash of the Nile, and has been mapped as a swamp ; but 
Purvis ^ says that after careful observation he has been able to map it 
as one of the chief rivers carrying off the waters from Mount Elgon 
to the lake, and thence to the Nile. 
Edward and Albert Nyanzas. — The Albert Edward ^ and 
Albert Nyanzas, and the Semliki River which connects them, lie in 
the western arm of the great depression of East Africa and drain to 
the Nile ; while Lakes Kivu and Tanganyika, farther south, send their 
surplus waters to the Congo. The dividing line between the north 
and south watersheds is now a range of volcanic cones which have 
blocked the valley between Lakes Kivu and Edward. It is 
believed that these are of comparatively recent origin, and that 
formerly Lake Kivu drained to the north — a view supported by the 
similarity observed between the living shells in Lake Kivu and the 
dead shells in the cuttings of the Ruchuru River flowing into 
Edward Nyanza, and also by the fact that the fauna of Lake 
Tanganyika is entirely distinct from that of Lake Kivu. Moreover, 
Lake Kivu is very deep, and the upper part of the gorge through 
which its outlet, the Rusisi, flows in leaving the lake is stated to be 
but little worn, so that the river is not of very great antiquity. 
When the volcanic dam north of Lake Kivu was first formed, its 
effects would be felt to the north much sooner than to the south, 
for it would mean that the whole drainage area of Kivu was cut off" 
from the Nile. There is evidence in history that on the Upper Nile 
there existed huge lakes which have now disappeared, and it is quite 
probable that the shrinkage of the upper waters of the great river of 
Egypt which appears to have taken place is directly connected 
with the formation of the Kivu dam. After this dam was formed, 
not only must the Nile supply have shrunk by the loss of the very 
large amount of water collected from the Kivu drainage area, but 
the water to the south of the volcanic dam must have slowly 
risen year after year, and probably century after century, until it 
1 Through Ugmida to Mount Elgon, p. 242, London, 1909. 
2 Albert Edward Nyanza is now to be called Edward Nyanza (or Lake 
Edward), so as to avoid confusion with Albert Nyanza (or Lake Albert). See 
Geogr. Journ., vol. xxxiv. p. 129, 1909. 
