NEWBOLD ON THE GEOLOGY OF EGYPT. 325 
their pinnacles and dome-shaped masses render the aspect more varied 
and irregular. 
The deserts present a series of undulating plains; sometimes 
studded with low irregular hilly clusters, and covered for the most 
part with unproductive saline, often calcareous and gypseous, sand, 
marl, and gravel, the layers of which are broken up by the drainage- 
channels of the unfrequent rains, and often denuded from causes no 
longer in action. The existence of springs of fresh water, both in 
the desert and mountainous tracts, is marked by spots of the most 
refreshing verdure, known under the term Oases. These I am induced 
to regard simply as valleys or depressions supplied either from such 
springs, or from the drainage-water of the desert, that finds its way 
below the surface of the sands, and lodges in the impervious marl or 
clay-covered bottoms of the oases, keeping up a scanty, though 
almost constant, supply of water. In a few places, at low levels, the 
water appears to be supplied by percolation from the Nile. In a 
climate like that of Egypt, water alone, even on the sands of a desert, 
rapidly produces vegetation, from the successive decay and reproduc- 
tion of which a layer of vegetable mould results, that goes on in- 
creasing in depth and extent proportionate to the supply of water. 
The height of the desert varies considerably: the extreme eleva- 
tion attained between Suez and Cairo is about 700 feet above the 
ocean. Its general character between the Nile and Red Sea is that 
of an elevated plateau, with a flattish irregular superficies, rising 
towards the centre, and gradually sinking on either side till it termi- 
nates on the shores of the Red Sea and the borders of the Nile in 
abrupt escarpments or steep descents. 
The levels taken through the marshy and flat extent between 
Suez and Pelusium give a depth of 24 feet below the sea-level*. 
The aspect presented by the valley and delta of the Nile varies 
according to the seasons. During the inundation they exhibit a vast 
freshwater lake, whose surface is studded by a number of palm- 
shaded hamlets. After the subsidence of the waters, one sees a 
waving line of brilliant verdure winding through the sterile expanse 
of desert on either side of the upper part of the river, and girt in 
until it arrives at the verdant expanse of the delta, by white mural 
cliffs. The line of demarcation between the sandy desert and the 
dark alluvium of the Nile is abrupt and well-defined. After the 
grain is cut and carried off the ground, the charm is dispelled, and 
the eye turns away from the tedious prospect of one monotonous, 
brown, dusty, arid plain, through which the sluggish Nile slowly 
winds its straitened muddy course. The extreme flatness of the 
delta may be conceived from the circumstance of the canal, which 
unites Alexandria with the Nile, running its whole extent (about 
sixty miles) without a.single lock: and the whole superficies of 
Egypt, from the first cataracts to the Mediterranean, presents an in- 
clination to the north of only two inches per milet. The descent a 
little north of Assuan is as much as seven inches, but lessens as it 
approaches the delta. 
* Laborde, p. 263. + Mr. Wallace, quoted by Mr. St. John, Travels, p. 354. 
VOL. IV.—PART I. 2B 
