130 
DESCRIPTIONS OF EGYPT. 
it is drifted from the interior of Africa. By im- 
peding the progress of this moving desolation, and 
rendering the incessant agency of the wind less 
dangerous, it has preserved the cultivated banks 
of the Nile from destruction, and permitted the 
natives, who attribute this effect to the talismanic 
power of the Sphinx of the Pyramids, to enjoy 
their dreams of superstitious credulity. In some 
places, however, the progress of the sands is 
marked in a picturesque manner, by the large and 
beautiful sycamores, originally rooted in the allu- 
vial soil, which wither in solitary grandeur on the 
arid downs, now covered with sand. In the val- 
ley of the dry river, various kinds of stones are 
found, which appear to have been brought from 
the primitive mountains of Upper Egypt ; as silex 
and siliceous stones, gypsum, quartz, and quart- 
zose crystallizations, geodes, jasper, and Egyptian 
pebbles. But the most curious production of the 
valley is the petrified wood in which it abounds. 
Andreossi found some entire trees, eighteen paces 
in length, in a state of petrifaction. In most in- 
stances, the wood is changed into agate ; but 
where the crystallization is more imperfect, that 
part which formed the substance of the wood ex- 
hibits a scaly texture, invested with a hard exter- 
nal envelope. Here Andreossi likewise found the 
vertebrae of a large fish, which appeared to be mi- 
neralized. Sicard asserts, that in this valley he 
