AFRICA by the separation of the river into the Rosetta and Damietta branches. The width of the Nile differs greatly in different sections ; there are many places where it is several miles broad. The average velocity of its current is 2J in. an hour. In Egypt the maximum height of the annual flood is between 30 and 35 ft., and is attained between the middle of September and the middle of October, the river being lowest in April and May. The lakes of Africa are closely associated with the continental river systems, especially in the case of the Nile. That river proceeds from a region of fresh-water lakes unrivalled except by the great lakes of N. America. Three of these lakes have been visited by Europeans, but no one of them has been completely explored. In 1858 Lake Tanganyi- ka (so called from a native word meaning the meeting place of waters) was discovered by R. F. Burton and J. H. Speke, captains in the British army, whose names have since become famous in the history of African exploration. It is a long and narrow sheet of water, situated between lat. 3 10' and 7 50' S., with its cen- tre in about Ion. 30 E. according to most of the authorities, although Kiepert places it con- siderably W. of that meridian. Burton esti- mates its total length at 250 m., its mean breadth at 20 m., and its altitude above the sea at 1,850 ft. Its waters are pure and deep. The Victoria N'yanza, which was seen by Speke in 1858, and subsequently visited by him in company with Oapt. Grant, lies some 200 m. N". E. of Lake Tanganyika, with a lofty moun- tain district intervening. Among its native names are Nyanja, Ukere, and Ukerewe. Ac- cording to Speke's observations in 1862, its height above the ocean is 3,308 ft. Its north- ern outlet, which flows over a picturesque cat- aract called Ripon Falls, in the immediate vicin- ity of the lake, was believed by Speke to be the veritable White Nile, although he was told by the natives that this stream passed into another vast inland sea, which they called the Luta Nzige. This statement was confirmed by the dis- coveries of Sir Samuel Baker and his wife in 1864, when they traversed the eastern shores of the Luta Nzige on which they bestowed the name Albert N'yanza traced its connection with the Victoria lake on the east, and beheld the Nile emerging from it on the north. This vast ex- panse is embosomed amid noble mountains of great beauty, and is 2,720 ft. above the level of the sea much lower than the Victoria N'yanza. Its area is unknown, though Baker estimated its width near the northern end at 60 m. Still another lake belonging to this aggregation and called Bahari Ngo, or Baringo, is supposed to lie E. of the Victoria N'yanza. Capt. Burton per- sistently asserts a belief that the latter will ul- timately be ascertained to be, not a single lake, but a vast marshy region of many lakes. Far removed from this system, in lat. 20 19' S. and Ion. 22 E., is Lake Ngami, about midway between the respective coasts of the continent. It is 3,713 ft. above the ocean, from 50 to 70 m. long, quite shallow, and supposed to be gradually contracting its shores. Livingstone discovered it in 1849, and followed its outlet, the river Zooga, some distance toward the dis- trict now known to be watered by the Limpopo. Ten years later Livingstone also discovered the more important Lake Nyassa, which is sit- uated about 300 m. from the E. coast and N. of the Zambesi delta, with which it is connect- ed by the river Shire. It lies in a valley sur- rounded by eminences, at a height above the sea of about 1,500 ft. Its width is from 20 to 60 m., and its entire length is estimated at not less than 200 m., although the northern ex- tremity has never yet been visited by white men. Its waters are very deep. In the clear, dry season their surface is ruffled by boisterous southeasterly gales, which render navigation perilous. Shirwa, a much smaller lake than N'yassa, but exceeding it in elevation by about 500 ft., is situated among the mountains on the S. E., 30 m. distant. The principal lake of Abyssinia is Tsana or Dembea, covering an area of 1,400 sq. m. in the centre of a plain over 6,000 ft. in altitude, on which the climate is that of perpetual spring. In the same coun- try is also the beautiful little lake of Ashangi, enclosed on all sides by mountains towering above the plateau on which it rests. The chief body of water in central Africa is Lake Tchad, which is extremely shallow, being only from 8 to 15 ft. in depth. Its area appears to vary somewhat in different seasons. Its eleva- tion above the sea is 840 ft. The geology of Abyssinia is better known than that of any other single region of Africa. The foundation of the plateau is metamorphic rock extending to a height of some 8,000 ft. above the sea, and surmounted principally by bedded traps, although in a few instances limestones and sandstones are enclosed between these forma- tions. A line of rocks of volcanic origin skirts the Red sea coast, along which there is also a fringe of coral, embracing Massowa and the neighboring islands. The precipitous gor- ges through which so many of the Abyssinian rivers flow have probably been worn down through the solid rock to their present depth by the ceaseless action of water exerted through enormous periods of time. The ra- vine of the Tacazze, one of the streams which unite to form the Blue Nile, is 3,000 ft. deep. A firm clay underlies the deserts of N. Africa. On the W. boundary of Egypt limestones oc- cur, and granite, sandstone, and argillaceous slates are found in Nubia. The deltas of all the great rivers are alluvial deposits. The geological structure of the S. African tableland, according to Murchison, is unique in having maintained the same terrestrial and lacustrine conditions since the secondary epoch. _ No fos- sil bones have been found in this territory ex- cept such as belong to species of animals which still inhabit it. There are tertiary rocks at the Mombas mission in Zanzibar, near the mouth of the Zambesi, and at the Cape ; but these
