WEST AFRICA	453
African, and is obtained partly from the Katanga itself, and partly
from Ruanda and Urundi, Rhodesia, and Nyasaland. In order to
avoid the necessity of importing all the food-stuffs required by the
mining population, attempts are being made to develop farming on
European lines in some of the districts which are suitable for white
settlement, but progress in this direction is slow. In the northern
parts of the Katanga, important deposits of tin have been discovered
on the north-west slopes of the Mitumba and Kibara mountains;
they have been worked near Kiambi, but the output is still small.
Gold and diamonds axe also known to exist, and from one of the
copper mines near Kambove is now obtained nearly the whole of
the uranium from which the world's supply of radium is produced.
other regions. In Mayumbe, where climatic conditions are
rather more favourable to Europeans than in the Central Basin,
there are various plantations upon which cacao and other crops are
grown. The native population of the savannas and grasslands is
mainly engaged in the cultivation of cereals, and in the east in stock-
raising. In some of these districts cotton growing seems likely to
become an important pursuit. The valleys of the Uele and Ubangi
in the north and of the Kasai and Sankura in the south produce
a large part of the cotton crop of the colony, which was 110,000 tons
in 1937. Gold is found in various parts of the Congo, but the greater
part of the output comes from the placer deposits along the head-
streams of the Ituri, in the northern part of the Eastern Highlands.
Kilo is the centre of this mining area. Alluvial diamonds are obtained
in the southern Kasai and Sankuru regions, and the Belgian Congo
now ranks next to South Africa as a producer of precious stones.
Coal is found near Bukama.
communications. Within the colony, the Congo and its tribu-
taries, of which the most important are the Ubangi and the Kasai-
Sankuru, offer over 8,000 miles of waterway, the greater part of
which is navigable by steamers. Unfortunately, the fairway of
these rivers is often interrupted by falls and rapids, or obstructed
by sandbanks, and their courses require to be regularized, where
possible, before full advantage can be taken of them. The earlier
railways in the country were designed to link up the navigable
reaches of the Congo. One was constructed between Matadi and
Leopoldville to circumvent the series of rapids by which the Congo *
descends from the Central Basin to its estuary ; another runs from