nishes. Rarely, indeed, is nature absolutely a
niggard. Mostly she gives far more than is needed, but the improvidence
or the apathy of man allows her gifts to run to waste. Careful and
provident husbanding of her store will generally make it suffice for all
man's needs and requirements. Sometimes this has been effected in a
thirsty land by conducting all the rills and brooks that flow from the
highlands or hills into subterranean conduits, where they are shielded
from the sun's rays, and prolonging these ducts for miles upon miles,
till every drop of the precious fluid has been utilized for irrigation.
Such is the _kareez_ or _kanat_ system of Persia. In other places vast
efforts have been made to detain the abundant supply of rain which
nature commonly provides in the spring of the year, to store it, and
prevent it from flowing off down the river-courses to the sea, where it
is absolutely lost. For this purpose, either huge reservoirs must be
constructed by the hand of man, or else advantage must be taken of some
facility which nature offers for storing the water in convenient
situations. Valleys may be blocked by massive dams, and millions of
gallons thus imprisoned for future use, as is done in many parts of the
North of England, but for manufacturing and not for irrigation purposes.
Or naturally land-locked basins may be found, and the overflow of
streams at their flood-time turned into them and arrested, to be made
use of later in the year.

In Egypt the one and only valley was that of the Nile, and the one and
only stream that which had formed it, and flowed along it, at a lower or
higher level, ceaselessly. It might perhaps have been possible for
Egyptian engineering skill to have blocked the valley at Silsilis, or at
the Gebelein, and to have thus turned Upper Egypt into a huge reservoir
always full, and always capable of supplying Lower Egypt with enough
water to eke out a deficient inundation. But this could only have been
done by an enormous work, very difficult to construct, and at the
sacrifice of several hundred square miles of fertile territory, thickly
inhabited, which would have been covered permanently by the artificial
lake. Moreover, the Egyptians would have known that such an embankment
can under no circumstances be absolutely secure, and may have foreseen
that its rupture would spread destruction over the whole of the lower
country. Amenemhat, at any rate, did not venture to adopt so bold a
design