150 
THE DESICCATION OF AFKICA 
central portion is everywhere covered with great areas of 
water-loving vegetation, such as rush and other plants, which 
require shallow but permanent water. Thus evaporation is 
arrested. These areas imperceptibly merge with the sudd 
of the lake, chiefly composed of papyrus, of which there are 
huge floating islands interspersed by areas of open water. 
On the south and east sides of the lake it is just about 
impossible to say when the lake proper is reached. On the 
north-west shores the lake is bounded by cliffs, rising in places 
to about fifty feet with sand beaches below. There are square 
miles of open water, too deep generally for aquatic plants and 
evidently kept clear of floating sudd by the prevailing winds 
from the north extremity, and very rapid desiccation is thus 
not so apparent in this Bangueulu basin of granite and allied 
rock which has decomposed into the impermeable kaolin 
clay. In two places I found outcrop ridges of granite near 
the lake laid bare by running water. A strange sight where 
stone is otherwise absent. 
The Luapula River, which forms the Belgo-British boundary, 
is a large river 500 to 600 yards wide in parts. It is flanked 
for the most part by large lagoons and swamps, especially on 
the Belgian side. Nevertheless, examination of the adjacent 
country leaves no doubt that these lagoons are but remnants 
of extensive chains of lakes through which the river has run 
as a drain, like water draining from a mud flat. After leaving 
Bangueulu and turning north it flows over a rock bed of hori- 
zontal strata, which produce short falls and rapids for about 
half its length. From thence onwards to Lake Mweru, lagoons 
and swamps are much in evidence, and through which the 
river runs. 
Lake Mweru , — This well-defined lake, some seventy miles 
long by about thirty wide, does not show signs of extreme 
shrinkage, although a slight rise in its present level would again 
inundate its old western extension, now a fertile plain about 
twenty miles by ten. Within a mile of the north-east end 
are dry flats and diminishing swamps, but the height of the 
intervening land ridges leads to the conclusion that these 
flats belong to the Luvna and Lualaba (Upper Congo) system 
of drainage. The same can be said of the Choma river and 
