CAIRO TO KISUMU made so that the water can be let in and out and allowed to pass through at will.

It is at flood time that the Nile valley gets its rich feed of Abyssinian mud. This is brought down in part by the Blue Nile, but more abundantly by the Atbara, or Black Nile. It is carried by the inundation all over Egypt and by means of irrigation conducted to nearly every farm. After the floods subside the muddy waters grow clear again. The Blue Nile and the Black Nile become almost dry, and the white water of the main, or Victoria Nile, is about all that Egypt has. It is this white water that is stored up by the Aswan Dam, and it feeds the country in much the same way as our irrigation canals do, with water only and not with a thick mixture of water and mud as in the times of the overflow.

For thousands of years these rivers have been pouring down through this Nile valley; but whenever the rains have been scanty in the highlands of Abyssinia and in Central Africa the main stream has not been high enough to reach the whole country. Most of the lands could be inundated only once a year, and if the Nile was especially low some could have no water at all. By the present system Egypt has water all the year round, and enough to make it produce two or three crops every twelve months.

I have been much interested in the irrigation works of the past. The whole of the Nile valley above Cairo is cut up into a series of basins. For six hundred or seven hundred miles north of this point the valley slopes very gradually and, in order to save the water, dikes have been made across it and embankments run parallel with the river, turning the whole country into a series of basin-like terraces, each containing from five thousand to fifteen 130