are

The distribution of Karroo rocks in the Mafungabusi and the conditions under which they were accumulated frequently found to be matters on which some information is desirable, in order that a comparison may be made with the succession of the same system of rocks in the Wankie coalfield (3)* some 160 miles to the west, and with the Upper Karroo strata to the north-west of Bulawayo (4 and 5), which are the only localities that have been mapped by the Geological Survey in detail. A part of the Mafungabusi is included in the traverses that formed the basis of the introductory paper to the geology of the region by the writer in 1903 (1), while Mr. C. E. Parsons in 1903 gave a section, with notes of a route he had made from Gwelo to the Zambezi.

As the writer had made journeys across the region many years ago and taken route maps and geological notes on each occasion it has been suggested that he should look up these records for publication. Fragmentary as each single section must be owing to the circumstances in which it was made, the piecing together of the whole presents evidence on which the conclusions around it in this paper may be reasonably based. But it is not presented as being incapable of error.

II. PHYSICAL FEATURES.

The region known as the Mafungabusi lies in the Zambezi basin and on the west of the Umniati River.† It includes the head-streams of the Sesami and Bume Rivers, flowing northnorth-west, the Ngondomo vlei circling round the south, and several eastward running tributaries of the Umniati, namely, the Mzongwe, Nyoripakwe and Paruka. Cartographically it is placed between 17° 40′ 00′′ S. and 18° 20' 00" S., while the meridian of 28° 45′ 00′′ E. cuts through its centre.

*

The numbers in brackets refer to the papers listed in the References at the end of this memoir. These papers are discussed in Section V of this memoir.

In many Rhodesian rivers the name applied to different parts of its course varies. This river is known as Umniati as far as its confluence with the Umfuli, then as the Sanyati. Ume, Bume and Ome (Omay) are local terms for the other river referred to.

that faces the lower lying ground on the north-west and east. On the map attached hereto (Fig. 1) this tableland appears as a wedge pushing between the valleys and forming the watershed of the Bume and Umniati Rivers, the point being

The name is, however, more generally applied to the remnant of a dissected tableland of sedimentary and volcanic rocks that in the south overlap on to the uplands of crystalline schists, the northern margin being defined by an escarpment

formed by a conical hall, named Chidomwe, and which is separated by a wind-gap from the larger Denamwe Hill. A broken chain of flat-topped outliers of mesa type, extending eighteen miles to the north-west, shows that once the tableland continued over a considerable region in that direction, but which has since been cut back by erosion to the line of its present margin, that now stretches many miles to the southwest, where it had been previously mapped by me as the "Great Escarpment" (1). This feature includes the Mafungabusi Mountain, the wedge-shaped block described above. A view of the eastern side of this dissected plateau, taken from the Mzongwe Drift, is given in Fig. 2.

To the north-north-east of the mountain the flat country is continuous, with wide mopani forests and baobabs. The soil is deep and cold, and there are frequent patches of wellrounded pebbles and occasional pans. The area seems to be a plain that has resulted from the disintegration and denudation of Karroo beds. Pre-Karroo sedimentary rocks appear in the Umniati around Impali village and at the junction of the Umtanji, and form the floor of the Karroo area in this vicinity.

West of the mountains there is a great change from the above-mentioned conditions. Erosion is here relative to the Bume River sytem, 2,600 feet in altitude in the basin around Gorodema, or to the Sesami River system in the Inyoka country, and in both of which it has denuded the Matabola beds, so that there are exposed large areas of clays and coals. These rocks give rise to the cold, sun-cracked soils so favoured by mopani forests, or covered by short thorn and a species of burr or "rats-bane." Alluvial deposits in the river banks and creeks are favourable, to_rich jungle growth, but under cultivation these patches produce good crops of corn and tobacco. Soils from the basaltic rocks and the lighter sandy ground from the Forest sandstone are clad with almost impenetrable brakes and baobab trees, but when put to the test and cultivated, as by the Inyoka Tobacco Company, yield very fine tobacco. Native-grown "Inyoka tobacco" put up into conical loaves, has long been desired by the Matabele. The lower altitude and the shutting off by the mountains of the cool south-east breeze of the plateau seem to account for the climatic change necessary to a more tropical botanical development.

Many permanent springs emerge at the base of the basalt, but the water is absorbed into sandy stream courses after passing but a short distance.

There were at one time several wagon roads into the neighbourhood, but they are fallen into disuse owing to the prevalence of the tsetse fly. Rob's Drift, on the Umniati, is the terminus of a road from Gatooma. In the absence of roads, travellers have to make use of the native footpaths, and those which were traversed by the writer are marked in the map.