The mountainous edge of the table-land, with its terminal projections, Senegambia and Abyssinia, which separate the northern from the southern deserts, are the principal source of running water in Africa. Various rivers have their origin in these mountainous regions, of which the Nile and the Niger yield in size only to some of the great Asiatic and American rivers. In importance and historical interest the Nile is inferior to none. Two large rivers unite their streams to form the Nile—the Bahr-el-Abiad, or White Nile, and the Bahr-el-Azrek, or Blue Nile; but the latter is so far inferior to the Bahr-el-Abiad that it may almost be regarded as a tributary. The main stream has never been ascended by any traveller above 4° 42ʹ 42ʺ north latitude, where a ledge of gneiss crossing it arrested the progress of the second expedition sent by the Viceroy of Egypt to discover its source. Bahr-el-Abiad, or the true Nile, is supposed, from the report of the natives, to rise, under the name of the Tubiri, at a comparatively small distance from the sea, in the country of Mono Moézi, which is a continuation of the high plateau of Abyssinia, situate to the north of the great Lake Zambéze, or N’yassi. The natives say that it flows from the lake itself; at all events it seems to be pretty certain that its origin is in the mountainous or hilly country of Mono Moézi, a word which in all the languages of that part of Africa signifies the Moon: hence, the Nile has been said, since the days of Ptolemy, to rise in the Mountains of the Moon. Amidst many windings it takes a general direction towards the N.E. to the 14th northern parallel, whence it follows the same course till its junction near Khartum with the Blue Nile in the plains of Sennaar. The Shoaberri and Godjeb, the chief affluents of the White Nile, come from the east; the former makes a great circuit round the country of Berri before it falls into the Nile, and the Godjeb, which has its origin in the great forest already mentioned, in the Galla country, south of Abyssinia, makes a similar spiral détour round Kaffa, and under the name of Subat joins the Nile, which it enlarges to nearly double its size.