th
faces in little hollows scooped in the sand.

Perhaps the full blast of the simoom may last an hour--perhaps two or
even three hours. In lighter strain it may continue a whole day. When,
finally, it ceases the air is thick with fine dust; one can see scarcely
a rod away. Sun and sky are hidden, and the blackness of a tornado or of
a London fog prevails. The fine dust floating in the air may not settle
for several days. Perhaps a week afterward there may be a haze that
partly obscures the sun. The dust, finer than the finest flour, pervades
everything in the desert. One's clothing is full of it; one's hair
becomes harsh and matted; the skin becomes rough, cracks and peels; the
eyes are inflamed; mouth, lips, and nostrils are swollen. But the great
bodily discomfort resulting from the simoom does not last forever; it
gives place to bodily irritation of some other sort, which is indeed a
grateful change merely because it is a change.

The sand dunes of the Sahara are interesting to those who are not
compelled to travel among them, but to the unfortunates who traverse
them they are almost heart-breaking. Imagine oneself standing on an
elevation a few hundred feet higher than the surrounding country. There
is but one landscape--waves upon waves of the loose rock waste, for
convenience called sand, as far as the eye can reach. Sometimes the
waves are in long windrows, but oftener they are short and choppy like
the surface waves of midocean.

Unlike the ocean waves, in which only the form moves forward, while the
water composing it moves up and down only, the sand dune and the
material of which it is composed are both moving in the direction of
the wind. A breeze even of five or six miles an hour will keep the
lighter surface dust moving freely, while a twelve-mile wind will not
only sweep along much larger particles but it also carries more of them.
And just as the surface, or "skin," friction forms waves at the surface
of water, it also piles the desert sand in wave-like dunes.

The loose bits of rock waste are carried along, up the windward slope of
the dune until they roll over its crest, where, no longer impelled by
the wind, they come to rest. Thus, the crest, built forward by new
material constantly added, is advancing. Valleys are filled; old stream
channels are obliterated; and the inequalities of the surface are
levelled off until the whole landscape is one of shifting, drifting
sand.

Notwithstanding all th