The reader will observe, by referring once more to the map, that south of the great rainless region of which we are speaking, there lie groups and ranges of mountains in Abyssinia, called the Mountains of the Moon. These mountains are near the equator, and the relation which they sustain to the surrounding seas, and to currents of wind which blow in that quarter of the world, is such, that they bring down from the atmosphere, especially in certain seasons of the year, vast and continual torrents of rain. The water which thus falls drenches the mountain sides and deluges the valleys. There is a great portion of it which can not flow to the southward or eastward toward the sea, as the whole country consists, in those directions, of continuous tracts of elevated land. The rush of water thus turns to the northward, and, pressing on across the desert through the great central valley which we have referred to above, it finds an outlet, at last, in the Mediterranean, at a point two thousand miles distant from the place where the immense condenser drew it from the skies. The river thus created is the Nile. It is formed, in a word, by the surplus waters of a district inundated with rains, in their progress across a rainless desert, seeking the sea. If the surplus of water upon the Abyssinian mountains had been constant and uniform, the stream, in its passage across the desert, would have communicated very little fertility to the barren sands which it traversed. The immediate banks of the river would have, perhaps, been fringed with verdure, but the influence of the irrigation would have extended no farther than the water itself could have reached, by percolation through the sand. But the flow of the water is not thus uniform and steady. In a certain season of the year the rains are incessant, and they descend with such abundance and profusion as almost to inundate the districts where they fall. Immense torrents stream down the mountain sides; the valleys are deluged; plains turn into morasses, and morasses into lakes. In a word, the country becomes half submerged, and the accumulated mass of waters would rush with great force and violence down the central valley of the desert, which forms their only outlet, if the passage were narrow, and if it made any considerable descent in its course to the sea. It is, however, not narrow, and the descent is very small. The depression in the surface of the desert, through which the water flows, is from five to ten miles wide, and, though it is nearly two thousand miles from the rainy district across the desert to the sea, the country for the whole distance is almost level. There is only sufficient descent, especially for the last thousand miles, to determine a very gentle current to the northward in the waters of the stream.