he waters are
held back for a distance of 140 miles up the course of the river. The
reservoir is filled during the months of January and February, and from
April to the end of August the water is let out for irrigation purposes
from the bottom of the reservoir, thus enabling the sediment, which
is of such value, to be carried out through the sluices. Four or five
waterings are allowed to percolate from it to the various regions which
are thus brought under cultivation, and besides this the main supply of
the river itself is artificially increased at the same time.

The dam has been constructed of granite ashlar taken from quarries near
Aswan. These quarries are the very same from which the ancient obelisks
were hewn. The amount of rock used was about one million tons in
weight. In building the dam it was found to be very difficult to lay the
foundation, since the bottom of the river proved to be unsound, although
in the preliminary reports it had been declared to be of solid granite.
In some instances it was found necessary to dig down for forty feet, in
order to lay a perfectly secure foundation on which the heavy wall could
be superimposed. This required much additional labour, and great risk
and damage was encountered during the progress of the work at the date
of the impending rise of the waters of the Nile. Rubble dams were
raised to ward off the waters from the point where it was necessary to
excavate. The holes were gradually filled with solid blocks of granite;
then the base of the structure, one hundred feet in width, was laid,
and the massive piers, capable of resisting the immense pressure of
the water during the height of the floods, were raised, and the whole
edifice was at length completed with great rapidity by the aid of
many thousand workmen, just before the rise in the Nile occurred. The
official opening of the dam took place on the 10th of December, 1902.

The dam at Aswan is the greatest irrigation project ever yet undertaken,
but is by no means the last one likely to be executed in relation to
the waters of the Nile. A smaller dam is to be constructed at Assiut,
in order to supply a system of irrigation in the neighbourhood of that
city, and also to carry water across to thousands of acres between this
region and Cairo. This project is planned somewhat after the design of
the barrage which is below Cairo.

It is impossible to forecast what engineering skill may have in
store for the future of Egyp