CAB129-37 — Page 308

Page 308

incised water courses are not found, and outcrops are few and far between. The main rock of the area is a coarse granitic rock of the Basement complex. The soils of the area belong to. Milne's group of plateau soils (Milne, 1936, 1947). Three main types are of practical importance.

On the crests of higher ridges a red medium loam is found lying on the granite. A massive ironstone layer is often observed in the profile in immediate contact with the granite, and filling the inequalities in its surface. Apart from organic matter accumulation in the surface layers the profile is otherwise uniform. The greater part of the Region, however, is covered by a pallid grey leached sandy topsoil, darkened by organic matter in the surface layers, overlying at six to twelve inches a horizon of considerable depth, which may range from bright red to pale yellow in colour, depending largely on the position of the exposure on the long, gentle slopes. In the infilled drainage channels is found a complex range of dark coloured alluvial soils varying in texture at the surface from sands to stiff clays. The lower layers are almost always heavy.

Nodular calcium carbonate does not appear in the soils of these areas except in the bases of the great termite mounds, where the accumulations may reach a thickness of several feet. This is particularly the case in the drainage area south of Ussinge. A few analytical figures for these soil types are available (section 11). Borehole water is in general soft.

'

The Urambo Region shows two important broad types of vegetation. The main type, covering with its many variants almost all of the Region, is the Brachygstegia-Isoberlinia open woodland (“miombo"), which is here seen not far from the northermost limit of its extent. Pterocarpus angolensis ("mlinga or "muninga "), which in Rhodesia and South Africa is not a common miombo constituent, is the most important economic timber. The woodland is from 15 to 40 feet high, and has a grass covered floor. The trees are typically spaced from 10 to 30 feet apart, and in the dry season a light vehicle can travel anywhere in the woods. The leaf canopy, although nearly continuous, is not dense, so that the woodland is not dark. Fierce fires sweep annually through the woods in the dry season. This community is the home of several species of tsetse fly, and in many sections of the Urambo area the infestation is very heavy.

The second main vegetation type of the area is the seasonally swampy grassland of the drainage lines. At the margins of the grassland there is often a zone in which trees are restricted to the termite mounds, giving a parklike appearance.

Land of this general type extends over many thousands of square miles in western Tanganyika, but communication difficulties will probably limit the Urambo development to a small number of units for some time to come.

Southern Province areas, Tanganyika (General)

The vast areas proposed for development in the Southern Province are as yet imperfectly known and little reliable topographic work has been done. The whole area lies in a rainfall zone of 30 to 40 inches, falling in a single season from late November to May, and at altitudes between 1,500 and 2,000 feet above sea level.

Topographically much of the area is in an advanced stage of peneplanation, particularly in the lands north of the Mbemkuru river and to the east of the Liwale-Tunduru scarp. The soils are varied, and for the most part not so far advanced towards senescence as those of the Urambo Region. Many are indeed still in a stage of late maturity. The main plant formations can be included under the headings of Brachystegia-Isoberlinia open woodland ("miombo ") of several types, Combretum--other species light open savannah, and swamp or drainage line grasslands. Pterocarpus angolensis occurs in both miombo Page 308 of 1097

and savannah. Page 308 of 1097

101

T

163