Lieut. Newbold on the Geology of Egypt. 221 
interior being partly filled with grit and conglomerate ; and he men- 
tions cases in which all ligneous structure had disappeared. The 
silicified wood varies in character from a white opake crust, which 
crumbles when handled, to agate and flint, and in colour from white 
to grey, brown and red. No decided seed-vessels or traces of leaves 
have been found. 
The author then describes the structure of Gebel Ahmar, situated 
on the northern limit of the ‘* Fossil Forest,” and of the intervening 
valley. Gebel Ahmar is an irregular ridge, a mile in length and 
half a mile in breadth, rising to the height of about 150 feet above 
the general level of the desert, and it is composed of conglomerate, 
grit and sandstone, the prevailing colour of the strata being red 
(Gebel Ahmar, Red Mountain). 
The stone has been so extensively quarried, and the mounds of 
rubbish are so numerous, that the original outline of the ridge has 
been obliterated; and its present rugged, conical aspect is due to 
those causes, and not to a supposed volcanic origin. The sandstone 
reposes, as elsewhere, on the marine limestone, passing near the 
line of junction into an ochreous, reddish and yellow clay, which 
contains veins of fibrous gypsum, selenite, salt, and, it is said, ba~ 
rytes. 
Both the sandstone and limestone abound in caverns, ‘‘ the resort 
of the hyznas that nightly prowl among the burial-grounds without 
the walls of Cairo. One of these dens, into which” Mr. Newbold 
descended, “ contained the recent dung of the unimal intermingled 
with human and other bones.” 
The valley which intervenes between Gebel Ahmar and the “ Fossil 
Forest” is excavated in the sandstone, the subjacent limestone being 
in some places exposed. 
The following inferences are drawn by Mr. Newbold from the 
phznomena presented by the deposit of petrified trees :— 
(1.) He is of opinion that this part of Egypt has twice formed 
the bed of the ocean, and been twice elevated above the surface of 
the water. 
(2.) That the fossil trees lived between these epochs, when they 
were submerged or drifted into the ocean, and were covered up bya 
bed of rolled pebbles or sand; and that they were afterwards raised 
to their present position. 
(3.) ‘That the elevation of the strata was effected gently and gra- 
dually, as the horizontal position is maintained. 
(4.) The retiring water is supposed to have removed the looser 
portions of the once continuous strata, and to have dispersed them 
with fragments of the fossil trees over the surface of the Egyptian 
and Libyan deserts, constituting the present accumulations of gravel 
and saline sands, 
(5.) From the little-worn aspect of the trunks, as well as the an- 
gularity and “nice adaptation” of many of the fractured portions 
near Cairo, it is inferred, that, in that locality at least, the specimens 
rest at no great distance from the spot on which they were silicified ; 
and from the vertical position of a few of the trunks, that they pro- 
