SANDS OF EGYPT. 533 



the quantity yet remaining on tlie borders of Egypt, that a waU 

 four or five feet high suffices for centuries to check its encroach- 

 ments. This is obvious to the eye of every observer who prefers 

 the true to the marvellous ; but the old-world fable of the over- 

 whelming 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 disap- 

 point the readers of their journals if they do not recount the 

 particulars of their escape from being buried aHve by a sand- 

 storm, and the popular demand for a " sensation " must be grati- 

 fied accordingly.* 



Another circumstance is necessary to be considered in estimat- 

 ing the danger to which the arable lands of Egypt are exposed. 

 The prevailing wind in the valley of the Kile and its borders is 



esting 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 I have picked up, in such 

 localities, rounded, irregularly broken fragments of agate, which had received 

 from the attrition of the sand as fine a polish as could be given them by the 

 wheel of the lapidary. The polish of the granite rocks at the First Cataract 

 of the Nile is due to the silicious slime transported by the water, and it must 

 have required coimtless ages to effect it. The smoothness of river pebbles is 

 due to a similar cause, combined with the attrition of the pebbles against each 

 other. 



Very interesting observations, by Blake, on the polishing of hard stones by 

 drifting sand will be found in the Pacific Bailroad Report, vol. v., pp. 92, 

 230, 231. 



The grinding and polishing power of sand has lately received a new and 

 most ingenious application in America. Jets of sand, and even of small par- 

 ticles of softer substances, thrown with a certain force, are found capable of 

 cutting the hardest minerals and metals. A block of corundum, some inches 

 thick, has been bored through in a few minutes by this process, and it prom- 

 ises to be highly useful in glass-cutting and other similar operations. 



* 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 Arabia, and the 

 testimony of the Bedouins he consulted, are to the same purpose. The dan- 

 gers of the simoom are of a different character, though they are certainly 

 aggravated by the blinding effects of the light particles of dust and sand 

 borne along by it, and by that of the inhalation of them upon the respiration. 



