If the surplus of water
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.
