10 [ No. 99 GEOGRAPHY will probably give them considerable economic impor tance in the future.

To the north -west of the Bia Mountains, and between them and the Hakannson Mountains, lies the lowland which is generally known as the rift-valley of Upemba. Lakes Upemba and Kisali are the largest remnants of the great lake which once occupied this region, but there are, in all, about thirty -five fluvial lagoons along the course of the Lualaba, and at times of high water much of the land is converted into marsh . The soil is fertile and the vegetation rich , but the district is unhealthy.

To the east of the Kundelungu lies the Mweru Luapula valley, where there are considerable tracts of alluvial soil. Many fertile districts exist along the course of the Luapula and to the south -west of Lake Mweru . Notwithstanding its heightover 3,000 ft. the country has a tropical climate, and much of it is covered with forest.

On the west of Lake Tanganyika from the Luvua to the Lukuga extends the mountainous region of the Marungu , which may be regarded as a transition zone between the Katanga proper and the Eastern Highlands.

Southern Kasai Basin.—To the west of the Katanga region the land merges into the Kasai country. This region is on the whole one of the least known parts of the Congo, but its general structure is comparatively simple. From the KasaiandSankuru rivers the land rises gradually to the plateau of South Africa. This plateau is much dissected by the numerous rivers which rise upon it and flow northward to join the Kasai.

On the plateau, where the land rises to an elevation of over 3,000 ft. , the rivers usually flow in shallow de pressions within which they expand or contract accord ing to the season of the year. Their banks are often marshy, and the intervening lands are also badly drained . As they go northward the rivers cut deeper