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, Maniça, Manhiça (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 35° along the major axis of the continent, between Lake Chad (north latitude 14° to 15°), and the Noka a Batletle or Hottentot Lake, known to the moderns as Ngami (south latitude 20° to 21°). 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.