SANDS OF EGYPT. 
459 
siderable is the quantity yet remaining on the borders of 
Egypt, that a wall four or five feet high suffices for centuries 
to check its encroachments. This is obvious to the eye of 
every observer who prefers the true to the marvellous; but 
the old-world fable of the overwhelming of caravans by the 
fearful simoom—which even the Arabs no longer repeat, if 
indeed they are the authors of it—is so thoroughly rooted in 
the imagination of Christendom that most desert travellers, of 
the tourist class, think they shall disappoint the readers of 
their journals if they do not recount the particulars of their 
escape from being buried alive by a sand storm, and the pop¬ 
ular demand for a “ sensation 55 must be gratified accordingly.* 
be taken up by it, like dust; they only roll along the surface from which 
they are detached, and, though moving with great velocity, they rarely 
rise to a greater height than three or four inches .”—Memoire sur les Dunes , 
Annales des Fonts et Ghaussees , 1833, ler s6mestre, p. 148. 
Andresen says that a wind, having a velocity of forty feet per second, 
is strong enough to raise particles of sand as high as the face and eyes of a 
man, but that, in general, it rolls along the ground, and is scarcely ever 
thrown more than to the height of a couple of yards from the surface. 
Even in these cases, it is carried forward by a hopping, not a continuous, 
motion; for a very narrow sheet or channel of water stops the drift en¬ 
tirely, all the sand dropping into it until it is filled up. 
The character of the motion of sand drifts is well illustrated by an in¬ 
teresting fact not much noticed hitherto by travellers in the East. In 
situations where the sand is driven through depressions in rock beds, or 
over deposits of silicious pebbles, the surface of the stone is worn and 
smoothed much more effectually than it could be by running water, and 
you may pick up, in such localities, rounded, irregularly broken fragments 
of agate, which have received from the attrition of the sand as fine a polish 
as could be given them by the wheel of the lapidary. 
Very interesting observations on the polishing of hard stones by drift¬ 
ing sand will be found in the Geological Report of William P. Blake : Pa¬ 
cific Railroad Report , vol. v, pp. 92, 230, 231. The same geologist observes, 
p. 242, that the sand of the Colorado desert does not rise high in the air, 
but bounds along on the surface or only a few inches above it. 
* Wilkinson says that, in much experience in the most sandy parts of 
the Libyan desert, and much inquiry of the best native sources, he never 
saw or heard of any instance of danger to man or beast from the mere 
accumulation of sand transported by the wind. Chesney’s observations in 
