t, the Nile mud is black enough to have given the land itself its
oldest name, Kem, or Kemi, which has the same meaning of "black." At
Khartum, where the White Nile joins the Blue Nile, the main branch has
a fall from its upper level in the region of the tropical lakes, four
thousand feet above the sea, to twelve hundred feet, while traversing
a distance of twenty-three hundred miles. From Khartum to the sea the
distance through which the waters of the Nile wend their way is about
eighteen hundred and forty miles. During the greater part of this course
the flow is level, the average descent being about eight inches per
mile. If it were not, therefore, for the obstruction met with in the
Nubian section, the course of the Nile would be everywhere navigable.
Although no perennial affluents enter the main stream lower down
than Khartum, the volume of the Nile remains with little diminution
throughout the entire distance to the Mediterranean. During the period
of low water the amount of water in different localities is still
uniform, notwithstanding all the irrigation, infiltration, and
evaporation constantly taking place. The only explanation which has been
given to this phenomenon is that there are hidden wells in the bed of
the Nile, and from their flow the waste is ever renewed.

As the earth revolves from west to east, the waters of the Nile tend
to be driven upon the right bank on the west, where the current is
constantly eating away the sandstone and limestone cliffs. For
this reason the left side of the river is far more fertile and well
cultivated than the right bank. Below Ombos the valley is narrowly
constructed, being but thirteen hundred yards in width, the cliffs
overhanging the river on either side, but at Thebes it broadens out to
nine or ten miles, and farther up, in the Keneh district, the valley is
twelve or fifteen miles in width. The river here approaches within sixty
miles of the Red Sea, and it is believed that a branch of the Nile once
flowed out into the sea in this direction.

[Illustration: 237.jpg THE PLAIN OF THEBES]

Seventy miles below Keneh the Nile throws from its left bank the Bahr
Yusef branch, a small current of 350 feet in breadth, which flows for
hundreds of miles through the broader strip of alluvial land between the
main stream and the Libyan escarpments. In the Beni-Suef district this
stream again bifurcates, the chief branch continuing to wind along the
Nile Valley to a point above