CHARACTERISTICS AND DISTRIBUTION OF LAKES 613 
Mediterranean through two main arms and numerous subordinate 
channels. The lakes in the delta include Lake Mariut, 112 square 
miles in area, Lake Edku, 104 square miles, Lake Borollos, 266 
square miles, and Lake Menzala, 745 square miles, which stand in 
hollows left by the failure of the river to fill its delta region up to a 
uniform level. The continual accumulation of fine silt raises the bed 
and banks of the stream until it flows in a channel a little above the 
adjoining country ; thus a breach made during a flood overthrow 
diverts it to one side or the other, and in the new course so given 
the raising process and the breaking away are repeated. The various 
lines of flow are marked by higher deposits than the intervening 
spaces, and the interlacing of old channels encloses a very shallow, 
faintly marked basin. 
The most remote head-stream of the Congo is the Chambezi, River Congo, 
which rises on the western slope of the plateau between Lakes Nyasa 
and Tanganyika, and flows south-west into the marshy Lake 
Bangweolo. Near the south point of that lake the river makes its 
exit through a vast marsh with isolated lakelets. It then turns north 
through Lake Mweru and descends to the forest -clad basin of western 
equatorial Africa ; traversing this in a majestic northward curve, 
and receiving vast supplies of water from many great tributaries, it 
finally turns south-west and cuts a way to the Atlantic Ocean through 
the western highlands about latitude 6° South (see fig. 74). 
Both Mweru and Bangweolo are merely shallow depressions which 
have been turned into lakes by the Upper Congo. 
Lake Bangweolo, 3700 feet above sea-level, is of such uncertain 
area, owing to its shores being fringed with marsh and overgrown with 
papyrus, that it is useless to give any guess at the mileage of its open 
surface, but it must contain. Sir H. Johnston says, at least 1500 
square miles of navigable water. The rivers running to it often 
flow through narrow swamps, many of which seem to have been at 
one time shallow lakes whose shrunken remains still show at places, 
like Lake Moir, near Serenji. These small swamps become larger and 
more frequent as the rivers approach one another, and at last become 
one vast dead-level morass, which in its north-western part changes 
from a dense mass of papyrus reeds to a sheet of open water, and 
is then known as Lake Bangweolo. The lake has covered a much 
larger area eastwards and up the Lukula, Chambezi, and Mansya 
Rivers, for the rivers that pour in on its north and east sides have 
been piling mud in its shallow bed for centuries and extending their 
deltas into it. 
Lake Mweru, 3189 feet above the sea (Lemaire, 1901), is 68 miles 
long by 24 miles broad. 
