PEOCEEDIJTGS OF GEOLOGICAL SOCIETIES. 
4G5 
"On the Geology of the Egyptian Desert." By Mr. H. Duckworth, 
F.G.S. — Egypt, with its desert tracts, covers an area of about 100,000 
square miles. In form it is an irregular parellelogram, the longest axis of 
which runs north and south. It is that desert tract, east of the Nile, 
which forms the subject of this communication, generally known as the 
" Egyptain Desert," and which, from its connection with the Overland 
Eoute and the Suez Caual scheme, has had more than an ordinary amount 
of attention directed to it. The desert wliich stretches between Cairo and 
Suez is more varied in aspect than those who are acquainted with it might 
be disposed to believe, the ground being everywhere broken up into a series 
of undulating tracts, or shallow ravines, called by the Arabs " Wadis," 
whilst the mountain ranges of Jebel Mukattara, Jebel !tleibun, and Jebel 
Attakah, form a complete barrier towards the south. The surface of the 
land presents generally the appearance of a gravelly beach, pebbles and 
angular fragments of jasper, chert, quartz, gypsum, and sandstone being 
largely intermingled with sand. Vegetation its not altogether absent, and 
in the Wadis several ligneous and herbaceous plants are found, among 
which are the Acacia jiigyptiaca, the Astrac/alus kamosus, and the JFa- 
gonia latifolia {Sieleri et tumidus). The height of the desert varies con- 
siderably, but its extreme elevation above the sea may be stated at about 
i 700 feet. Its general character is that of an elevated plateau, rising towards 
! the centre and gradually sinking until it terminates in bold escarpments 
on the banks of the Nile on one side, and on the shores of the Red Sea on 
the other. These cliffs are composed for the most part of Nummulitic 
limestone, which we find extensively developed throughout Egypt and 
Nubia and a great part of the Sinaitic peninsula. Overlying this limestone 
are patches of a sandstone formation, associated with calcareous gypsums 
and saline marls, and stretching from the Mediterranean Sea far into the 
Nubian and Libyan deserts. The absence of its bods at certain points 
has evidently been caused by denudation, and the sands and gravels of the 
desert may be regarded as the debris of this formation. The beds of this 
sandstone vary in thickness from a few inches to 180 to 200 feet. Silici- 
fied monocotyledonous wood is found in great abundance in this deposit, 
especiall}' in the vicinity of Cairo, where the remains are so well preserved, 
and of such magnitude, as to be popularly known as the " Petrified Forest." 
The wood-stems in question are invariably found in a horizontal position, 
and there is no evidence to show that they originally flourished in siiu. 
I Professor linger, of Vienna, states that the trees belong, without excep- 
' tion, to one species, for which he proposes the provisional name Nicolia 
^gyptiaca ; and further, that the sandstone in which they occur is strictly 
analogous to a formation containing wood-stems near Gleischenburg, in 
Styria. He supposes the masses of wood to have been drifted into a basin 
separated from the main sea, and filled with water saturated with silica, — 
an hypothesis which appears to me extremely probable. 
" On the Composition of Black Sandstone occurring in the Trias around 
Liverpool." By Mr. A. Norman Tate, F.C.S. — These deposits are found 
in the sandstone of Flaybrick, Storeton, Toxteth Park, and other places. 
The author's attention was directed to them by Mr. Morton, and he has 
since examined them chemically to ascertain their composition. On treat- 
ing them with hydrochloric acid, chlorine gas was evolved, and the dark- 
coloured portion dissolved, leaving a residue of white sand. A quantitative 
analysis showed that, next to silica, the principal ingredient was peroxide 
of manganese. One sample contained as much as 10 per cent, of that sub- 
stance, whilst in others the quantity did not exceed 3-5 per cent. To the 
I presence of this peroxide of manganese the black colour is evidently due. 
! VOL. VI. 3 o 
