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Bo re ep 
356 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
desert, drifted chiefly by the khamsin and the whirlwinds that fre- 
quently raise it up in vast moving columns from the surface of the 
surrounding wastes. These excavations and mounds are so numerous 
as to have obliterated the original outline of the ridge, a circumstance 
which, coupled with the dark colour of the rock and crystalline aspect 
of some varieties, has probably induced M. Linant to consider it of 
volcanic origin. The rock is composed of beds of pudding-stone and 
grit (a, a, fig. 9) passing to a compact crystalline sandstone, varying 
from a deep blood-red to yellow and white. From its generally dark 
red aspect this ridge has obtamed the Arab name of ‘‘Gebel Ahmar,” 
i.e. the Red Mountain. The pudding-stone imbeds pebbles of the 
same size and nature as those found in the bed contaming the fossil 
wood, fragments of which are here found among the quarries. It 
once formed, doubtless, a continuous portion now separated by the 
valley (B, fig. 9) just alluded to. 
Near the southern extremity of the ridge stand two cliffs of sand- 
stone higher than the rest; the one of a deep red and yellow colour 
and compact; the other white, more granular, and crystalime. In 
the former, one of those vertical clefts often seen in sandstones, pro- 
duced probably by contraction durmg the process of consolidation, 
has caused the displacement of a large mass of rock, but there is no- 
thing resembling the effect of voleanic agency. The rock reposes in ~ 
horizontal beds on the surface of the limestone already mentioned 
(c, c, fig. 9). The sandstone near the junction-line passes into an 
ochreous reddish and yellow clay containing veins of fibrous gypsum, 
incrustations of muriate of soda, and selenite. Barytes are said to be 
found in this layer. 
Both the limestone and sandstone abound in caverns, the resort of 
the hyzenas that nightly prowl among the burial-grounds without the 
walls of Cairo. One of these dens into which I descended contained 
the recent dung of this animal, mtermingled with human and other 
bones. 
The shallow valley (8, fig. 9), already mentioned, appears to have 
been hollowed out by the erosive action of water, which has not how- 
ever been so great as to destroy the entire bed of sandstone, portions 
of which, firmer than the rest (6, 6), have successfully resisted 
the current. The softer intermediate parts of the bed have been 
carried away, leaving the subjacent limestone denuded in some places. 
Around these and some waterworn blocks of the same rock the drifted 
sand has collected, forming dome-shaped and conical knolls, which 
impart a somewhat volcanic aspect to the surface. Around others 
was found a deposit of a stiff gypseous marl. Many of these knolls 
have not escaped the hands of the Egyptian quarriers. The harder 
and more compact varieties were used for statuary and architectural 
purposes, while the looser gritty beds were hewn into millstones. 
The more argillaceous beds in the limestone are broken up for whet- 
stones, while a fine greyish variety of clay is used by the women of 
Cairo for washing. 
I shall now conclude with a few remarks drawn from a considera- 
tion of the geological position of the petrifaction-bed. 
