Chapter X. Notes on the Nzadi or Congo River.
The homogeneous form of the African continent causes a whimsical family resemblance, allowing for the difference of northern and southern hemispheres, in its four arterial streams - the Nile and Niger, the Congo and Zambeze. I neglect the Limpopo, called in its lower bed Espirito Santo, Manica, Manhica (Manyisa), and Delagoa River; the Cunene (Nourse) River, the Orange River, and others, which would be first-rate streams in Europe, but are mere dwarfs in the presence of the four African giants. The Nile and Niger, being mainly tenanted by Moslemized and comparatively civilized races, have long been known, more or less, to Europe. The Zambeze, owing to the heroic labours of Dr. Livingstone, is fast becoming familiar to the civilized world; and the Congo is in these days (1873) beginning at last to receive the attention which it deserves. It is one of the noblest known to the world. Whilst the Mississippi drains a basin of 1,244,000 English square miles, and at Carrollton, in Louisiana, discharges as its mean volume for the year 675,000 cubic feet of water per second, the Congo, with a valley area of 800,000 square miles, rolls at least 2,500,000 feet. Moreover, should it prove a fact that the Nzadi receives the Chambeze and its lakes, the Bangweolo (or Bemba), the Moero, near which stands the capital of the Cazembe, the Kamalondo, Lui or Ulenge, "Lake Lincoln" (Chibungo), and other unvisited waters, its area of drainage will nearly equal that of the Nile.
The four arteries all arise in inner regions of the secondary age, subtended east and west by ghats, or containing mountains mostly of palaeozoic or primary formation, the upheaval of earthquakes and volcanoes. These rims must present four distinct water-sheds. The sea-ward slopes discharge their superabundance direct to the ocean often in broad estuaries like the Gambia and the Gaboon, still only surface drains; whilst the counterslopes pour inland, forming a network of flooded plains, perennial swamps, streams, and lakes. The latter, when evaporation will not balance the supply to a "sink," "escape from the basin of the central plateau-lands, and enter the ocean through deep lateral gorges, formed at some ancient period of elevation and disturbance, when the containing chains were subject to transverse fractures." All four head in the region of tropical rains, the home of the negro proper, extending 35deg. along the major axis of the continent, between Lake Chad (north latitude 14deg. to 15deg.), and the Noka a Batletle or Hottentot Lake, known to the moderns as Ngami (south latitude 20deg. to 21deg.). Consequently all are provided with lacustrine reservoirs of greater or smaller extent, and are subject to periodical inundations, varying in season, according as the sun is north or south of the line. Those of the northern hemisphere swell with the "summer rains of Ethiopia," a fact known in the case of the Nile to Democritus of Abdera (5th cent. B.C.), to Agatharchidas of Cnidos (2nd cent. B.C.) to Pomponius Nida, to Strabo (xvii. 1), who traces it through Aristotle up to Homer's "heaven-descended stream" and to Pliny (v. 10). For the same reason the reverse is the case with the two southern arteries; their high water, with certain limitations in the case of the Congo, is in our winter.
By the condition of their courses, all the four magnates are broken into cataracts and rapids at the gates where they burst through the lateral chains; the Mosi-wa-tunya (smoke that thunders) of the Zambeze, and the Ripon Falls discovered by Captains Speke and Grant upon the higher Nile, are the latest acquisitions to geography, whilst the "Mai waterfall," reported to break the Upper Congo, still awaits exploration. This accident of form suggests a division of navigation on the maritime section and on the plateau-bed which, in due time, will be connected, like the St. Lawrence, by canals and railways. All but the Nzadi, and perhaps even this, have deltas, where the divided stream, deficient in water-shed, finds its sluggish way to the sea.
The largest delta at present known is the Nigerian, whose base measures 155 direct geographical miles between the Rivers Kontoro east, and Benin west. Pliny (v. 9) makes the Nile delta extend 170 Roman miles, from the Canopic or African to the Pelusiac or Asiatic mouth, respectively distant from the apex 146 and 166 miles; the modern feature has been reduced to 80 miles from east to west, and a maximum of 90 from north to south. The Zambeze extends 58 miles between the Kilimani or northern and the west Luabo, Cuama or southern outlet-at least, if these mouths are not to be detached. The Nzadi is the smallest, measuring a maximum of only 12 to 15 miles from the Malela or Bananal Creek to the mangrove ditches of the southern shore.