Geographical Notes

Abstract

IN a previous number we referred to the return of M. Edouard Dupont, Director of the Brussels Natural History Museum, from his visit to the Congo for the purpose of scientific exploration. Some of the results of his visit he described the other day to the Belgian Society of Engineers. M. Dupont pointed out that the African interior is drained mainly by four great rivers—the Nile, the Niger, the Zambezi, and the Congo—each of which has to break through the low range that bounds the interior somewhat saucer-shaped table land. The Congo, before making its great final effort, is to some extent dammed back into the reservoir known as Stanley Pool. M. Dupont's journey extended from the mouth of the river to the embouchure of the Kassai. The subsoil of the Lower Congo he found to be a soft and impure limestone covered with sand and clay. The mountainous region begins before arriving at Boma, and may be divided into three sections, according to the composition and aspect of the rocks. There is in the first place granite, gneiss, mica-schist, quartzite, and amphibolic rocks, in strongly inclined beds, and extending from Fetish Rock, below Boma, to the neighbourhood of Isanghila. The river from Vivi rushes in a series of cataracts through a gorge 55 miles long. Then follow schists and sandstones; and a little beyond Isanghila, at the great bend of the Congo, appear masses of limestone, very similar to those of the Meuse, and which alternate with the schists for about 35 miles. Then follow schists and red sandstones to beyond Manyanga. At Isanghila the banks rise into walls, some 700 feet high, of rough-grained, almost horizontal sandstone. This ends at Stanley Pool, where begins the Upper Congo. There is an immediate change in the strata. Some coherent sandstones show themselves at the base of the new deposits, and are topped by a great mass of soft sandstone, of the whiteness of chalk. M. Dupont traced these new rocks to the mouth of the Kassai, where there was nothing to indicate that they soon came to an end. He believes, on the contrary, that they constitute the subsoil of the greater part of the Upper Congo. M. Dupont is convinced, from his observations on the Congo, that the waters in the interior of Central Africa were at one time accumulated in a great lake, of which Stanley Pool is the last remnant. Gradually rising to the height of the mountains that bordered the plateau, they at last overtopped them, and, rushing down towards the Atlantic, gradually scooped out the channel now occupied by the Lower Congo. Stanley Pool, he considers, is the final stage of this supposed great internal lake.