DESERT. FOSSIL-FOREST. 299 
more, rarely, individual trees lay isolated, frequently 70 feet 
long, some 120, and it is said even 140. Their colour is gene- 
rally dark reddish-brown: they are all chalcedony and agate 
of a coarse description, with the rings of the wood well preserved. 
The sandy limestone (full of shells) and soil of the Desert are 
white; so that this fossil vegetation contrasted curiously with the 
general appearance of the country. Here the Pacha had sunk 
a pit for coal, sapiently concluding that so much fossil-wood above- 
ground indicated no less below. He however did not get 
through the limestone rock, which is subjacent to the formation 
to which I presume the fossil-wood belongs. Contrasted with 
the surrounding sterility, this record of a once luxuriant vege- 
tation is a very impressive object, for it is not confined to 
a few miles only of Desert, but (I am given to understand) 
extends forty or fifty in one direction. Ido not at all suppose 
that these forests ever characterized the Desert, or the land now 
replaced by desert, in its present relation to the general features of 
Egypt. On the contrary, I expect that the fossil-trees were 
imbedded in layers of conglomerate and sandstone which have 
been gradually destroyed by the ocean, leaving the silicified trees to 
resist, for the greater part, the action of that surf by which the 
softer rock was triturated, forming the sand and pebbles of the 
Desert. About one hundred miles above Cairo the sandstone 
rocks commence and the limestone ceases; and as on the Nile 
behind Cairo detached masses of the same sandstone rock as the 
statue of Memphis is cut from occur, so it appears probable that — 
this pebbly bed with fossil-trees belonged to that series of rocks, - 
all of which, south of lat. 29°, are washed away, leaving only the - 
agatized trees, all grievously water-worn, many being ground up - 
with the sand into pebbles. A white snail was very abundant 
everywhere, feeding on the Zygophylla and cruciferous plants. 
This mollusk does not occur south of 29°, i.e., of the limit of 
the limestone. 
After lading my sorry beasts with as many specimens as they could 
conveniently carry, we turned back and arrived late in the evening — — 
at Cairo, thoroughly tired, drenched with perspiration, and very — — 
: 2L2 : 
