The White Nile being at a considerable height when the Blue rushes down its steep slopes, presents its brother Nile with a soft cushion into which it plunges, and is restrained by the _vis inertiae_ of the more slowly moving river, and, both united, pass on to form the great inundation of the year in Lower Egypt.

The Blue River brings down the heavier portion of the Nile deposit, while the White River comes down with the black finely divided matter from thousands of square miles of forest in Manyuema, which probably gave the Nile its name, and is in fact the real fertilizing ingredient in the mud that is annually left.
Some of the rivers in Manyuema, as the Luia and Machila, are of inky blackness, and make the whole main stream of a very Nilotic hue.

An acquaintance with these dark flowing rivers, and scores of rills of water tinged as dark as strong tea, was all my reward for plunging through the terrible Manyuema mud or "glaur." _26th December, 1872._--Along among the usual low tree-covered hills of red and yellow and green schists--paths wet and slippery.

Came to the Lofubu, fifteen yards broad and very deep, water clear, flowing north-west to join Luena or Kisaka, as the Lopopussi goes west too into Lofubu it becomes large as we saw.

We crossed by a bridge, and the donkey swam with men on each side of him.