The mountain-tops may rise 2000 or 3000 feet above their flanks, along which we wind, going perpetually up and down the steep ridges of which the country is but a succession.
Looking at the geology of the district, the plateaux on each side of the Rovuma are masses of grey sandstone, capped with masses of ferruginous conglomerate; apparently an aqueous deposit.

When we ascend the Rovuma about sixty miles, a great many pieces and blocks of silicified wood appear on the surface of the soil at the bottom of the slope up the plateaux.

This in Africa is a sure indication of the presence of coal beneath, but it was not observed cropping out; the plateaux are cut up in various directions by wadys well supplied with grass and trees on deep and somewhat sandy soil: but at the confluence of the Loendi highlands they appear in the far distance.

In the sands of the Loendi pieces of coal are quite common.[16] Before reaching the confluence of the Rovuma and Loendi, or say about ninety miles from the sea, the plateau is succeeded by a more level country, having detached granitic masses shooting up some 500 or 700 feet.

The sandstone of the plateau has at first been hardened, then quite metamorphosed into a chocolate-coloured schist.