552 SANDS OF EGYPT. 
Northern Africa, additions are constantly made to the mass by 
the prevalence of sea-winds, which transport, or, to speak more 
precisely, roll the finer beach-sand to considerable distances 
into the interior. But this is a very slow process, and the ex- 
ageerations of travellers have diffused a vast deal of popular 
error on the subject. 
Sands of Egypt. 
In the narrow valley of the Nile—which, above its bifurea- 
tion near Cairo, is, throughout Egypt and Nubia, generally 
bounded by precipitous cliffs—wherever a ravine or other con- 
siderable depression occurs in the wall of rock, one sees what 
seems a stream of desert sand pouring down, and common 
observers have hence concluded that the whole valley is in 
danger of being buried under a stratum of infertile soil. The 
ancient Egyptians apprehended this, and erected walls, often 
of unburnt brick, across the outlet of gorges and lateral val- 
leys, to check the flow of the sand-streams. In later ages, 
these walls have mostly fallen into decay, and no preventive 
measures against such encroachments are now resorted to. But 
the extent of the mischief to the soil of Egypt, and the future 
danger from this source, have been much overrated. The sand 
on the borders of the Nile is neither elevated so high by the 
wind, nor transported by that agency in so great masses, as is 
popularly supposed; and of that which is actually lifted or 
rolled and finally deposited by air-currents, a considerable 
rock, and when the sun parcheth them, the wind carries off the dust, and 
other sand is there none in that land.” — Viaggio, pp. 69, 70. 
In Arabia Petrza, when a wind, powerful enough to scour down below the 
ordinary surface of the desert and lay bare a fresh bed of stones, is followed 
by a sudden burst of sunshine, the dark agate pebbles are often cracked and 
broken by the heat ; and this is the true explanation of the occurrence of the 
fragments in situations where the action of fire is not probable. If the frag- 
ments are small enough to be rolled by the winds, they are in time ground 
down to sand and contribute to the stock of that material which covers the 
face of the desert, though the sand thus formed is but an infinitesimal pro- 
portion of the whole. 
