bare hill-slopes may be heated up to 140 deg. or more when
the sun bathes them, while during the night the radiation out to space
is so intense that the temperature sinks to freezing-point. Through
these continual alternations the rocks expand and contract repeatedly,
fissures are formed and fragments are detached and fall down. The
hardest rocks resist longest, and therefore they stand up like strange
walls and towers amidst the great desolation.

If we go another step westwards we come to the land of the Tuaregs.
There, too, we find hilly tracts and _hammadas_, sandy deserts and
oases, and in favourable spots excellent pastures. We have already
noticed in Timbuktu this small, sturdy desert people, easily recognised
by the veil which hides the lower part of the face. All Tuaregs wear
such a veil, and call those who do not "fly-mouths." They are powerfully
built, and of dark complexion, being of mixed negro blood from all the
slaves they have kidnapped in the Sudan. They are as dry and lean as the
ground on which they live, and nature in their country obliges them to
lead a nomad life. Wide, simple, and dreary is the desert, and simple
and free is the nomad's life. The hard struggle for existence has
sharpened their senses. They are acute observers, clever, crafty, and
artful. Distance is of no account to them, for they do not know what it
is to be tired. They fly on their swift dromedaries over half the
Sahara, and are a terror to their settled neighbours and to caravans. On
their raids they cover immense distances in a short time. To ride from
the heart of their country to the Sudan after booty is child's play to
them. They have made existence in many oases quite unendurable. What use
is it to till fields and rear palms when the Tuaregs always reap the
harvest? The French have had many fights with the Tuaregs, and the
railway which was to pass through their country and connect Algiers with
Timbuktu is still only a cherished project. Yet this tribe which has so
bravely defended its freedom against the stranger does not number more
than half a million people. The Tuaregs are not born to be slaves, and
we cannot but admire their thirst for freedom, their pride, and their
courage.

The desert here exhibits the difficult art of living. Even animals and
plants which are assigned to the desert are provided with special
faculties. Some of the animals, snakes and lizards for instance, can
live without water. Dromedaries can g