The two grand affluents of Abyssinia are, the Blue Nile and the
Atbara, which join the main stream respectively in N. lat. 15
degrees 30 minutes and 17 degrees 37 minutes. These rivers,
although streams of extreme grandeur during the period of the
Abyssinian rains, from the middle of June until September, are
reduced during the dry months to utter insignificance; the Blue
Nile becoming so shallow as to be unnavigable, and the Atbara
perfectly dry. At that time the water supply of Abyssinia having
ceased, Egypt depends solely upon the equatorial lakes and the
affluents of the White Nile, until the rainy season shall again
have flooded the two great Abyssinian arteries. That flood occurs
suddenly about the 20th of June, and the grand rush of water
pouring down the Blue Nile and the Atbara into the parent
channel, inundates Lower Egypt, and is the cause of its extreme
fertility.

Not only is the inundation the effect of the Abyssinian rains,
but the deposit of mud that has formed the Delta, and which is
annually precipitated by the rising waters, is also due to the
Abyssinian streams, more especially to the river Atbara, which,
known as the Bahr el Aswat (Black River), carries a larger
proportion of soil than any other tributary of the Nile;
therefore, to the Atbara, above all other rivers, must the wealth
and fertility of Egypt be attributed.

It may thus be stated: The equatorial lakes FEED Egypt; but the
Abyssinian rivers CAUSE THE INUNDATION.

This being a concise summary of the Nile system, I shall describe
twelve months' exploration, during which I examined every