'298 JOURNEY TO CENTRAL AFRICA.

stretch their ridges across the middle of Africa, in latitudes where the latest travellers find a plain as level as the sea. A few words, therefore, concerning the character and relative position of the different countries of which I have occasion to speak, may make these sketches of African life and landscapes more intelligible to many readers.

As far as southern Nubia, with the exception of the Oases in the Libyan Desert, the Nile is the only agent of productiveness. Beyond the narrow limits of his bounteous valley, there is little except red sand and naked rock, from the Red Sea to the Atlantic. On reaching lat. 19°, however, a change takes place in the desert landscapes. Here the tropical rains, which are unknown in Egypt and Northern Nubia, fail every summer, though in diminished quantity. The dry, gravelly plains, nevertheless, exhibit a scattering growth of grass and thorny shrubs, and springs are frequently found among the mountain ranges. As we proceed southward, the vegetation increases in quantity ; the grass no longer keeps the level of the plain, but climbs the mountain-sides, and before reaching Khartoum, in lat. 15° 40; north, we have passed the limit of the Desert The wide plains stretching thence eastward to the Atbara, and westward beyond Kordofan, are savannas of rank grass, crossed here and there by belts of the thorny mimosa, and differing little in aspect from the plains of California during the dry season. The Arabs who inhabit them are herdsmen, and own vast flocks of camels and sheep. The Nile here is no longer the sole river, and loses his title of " The Sea," which he owns in Egypt. The Atbara, which flows down to him from the Abyssinian Alps, has many tributaries of its own , the Blue Nile, between Khartoum and Sennaar, receives the large