72 Dr. John Ball—The Nile Valley and Gulf of Suez. 
sandstone-beds come to the surface, until near the centre of the valley 
one comes on Carboniferous rocks in the form of thin limestone-beds, 
intercalated in the sandstones, with abundance of such characteristic 
fossils as Spirdfer and Productus. There is no apparent unconformity 
anywhere in the series. ‘The upper sandstone beds, which are devoid 
of fossils, may therefore be here, as in the Nile Valley, of Cretaceous 
age, though the lower ones are certainly Carboniferous. ‘The apparent 
absence of any unconformity between Cretaceous and Carboniferous 
is a very striking fact; but it is not material to the argument con- 
cerning structure, the great point in this connexion being the absolute 
proof, furnished by the succession of fossiliferous beds, and their dips, 
that the Wadi Araba is an eroded anticline, and thus the very opposite 
of a rift or trough-fault. 
Another very significant feature of the valley is the way in which 
great masses of the hard Eocene lmestones have been let down by 
landslips at the faces of the limiting scarps, often forcing the softer 
Cretaceous beds below them outwards into highly-tilted, or even 
‘nearly vertical, positions. ‘Two causes may have worked to produce 
this. The softer, lower beds may have been eroded out so as to under- 
cut the upper, harder ones, and bring about their fall; cracking of the 
beds may have occurred during the formation of the anticline, which 
would help in the separation of the masses. Further, it would appear 
at least a possible explanation that the stresses set up by the daily 
expansion and contraction of the plateau-surface under the influence of 
the enormous diurnal variation of temperature may have produced 
clefts near the free edges of the plateaux ; and masses detached in this 
way on even a slight slope would tend to creep lower and lower under 
continual expansion and contraction. But whatever the cause of this 
faulting-down at the face, it is at least certain that it is only land- 
slipping on a large scale, and has nothing to do with the main 
tectonic structure of the valley. The Wadi Araba is an eroded 
anticline, its limiting scarps showing in places a step-like structure, 
due to local slipping down of the hard upper strata at the cliff-face. 
I have dwelt thus long on the Wadi Araba, because, while it 
presents the same phenomena as the Nile Valley and the Gulf of Suez 
on a magnificent scale, it possesses also the advantage, not shared by 
them, of being entirely exposed, so that one can examine its floor 
with the same care and detail as its sides. If the floor of the Wadi 
Araba were covered with alluvium or water, we should have an almost- 
exact resemblance to the Gulf of Suez and the Nile Valley. 
Turning now to the Gulf of Suez, which lies in close connexion 
with the Wadi Araba, though at right angles to it, an exactly similar, 
albeit somewhat more restricted, series of observations can be made. 
Leaving the Wadi Araba, I journeyed northwards along the coast, 
skirting the scarps of the North Galala plateau, which in places come 
so abruptly down to the sea that camels have to wade through the sea 
to round the bluffs. The Carboniferous beds, with their characteristic 
erinoids, were traced as far north as 29° 30’ of latitude, showing 
clearly that the eastern foot of the North Galala plateau exposes 
Carboniferous strata at its base. The North Galala plateau is thus 
thrust upwards along the western shore of the gulf, the beds dipping ~ 
