The Bahr-el-Abiad, or White river, as the main stream of the Nile is called, issues' from the northern extremity of this lake, between lat. 2° and 3° N., at an altitude of 2,720 ft., and flows northward through a mountainous and rocky region, over four cataracts, to Gondokoro, in lat. 5° 54' N. Here it emerges into a plain and becomes navigable without serious interruption as far as the upper i Nubian cataract. Near lat. 9° 30' N. it receives the tributary Bahr-el-Gazal from the west - an important river, not yet fully explored. The Blue Nile, or Bahr-el-Azrek, from the lofty plateau of Abyssinia, joins the White river at Khartoom; and still further N. it receives the Atbara from the same country. Below this point tropical rains are unknown, and not a single tributary, not even a rivulet, enters the Nile. For more than 1,000 m. it alone irrigates the long green valley which without it would be as barren as the bordering desert. In Nubia it descends over three successive falls, each of which is in reality merely a series of rapids, and which are known respectively as the first, second, and third cataracts, the first named and northernmost being at Syene, on the boundary between Egypt and Nubia, about 700 m. from the Mediterranean and (500 ft. above its surface.

The delta begins 90 m. from the sea, 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 2 1/2 m. 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 lon. 30° E. according to most of the authorities, although Kiepert places it con- siderably W. of that meridian.

Barton 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 vicinity 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 discoveries 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 persistently asserts a belief that the latter will ultimately 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 lon. 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 bo gradually contracting its shores. Livingstone discovered it in 1849, and followed its outlet, the river Zooga, some distance toward the district now known to be watered by the Limpopo. Ten years later Livingstone also discovered the more important Lake N'yassa, which is situated about 300 m. from the E. coast and N. of the Zambesi delta, with which it is connected by the river Shire. It lies in a valley surrounded 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 extremity 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 country 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 elevation 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 formations.