PHYSICAL FEATURES. xlv 
The physical features of the escarpment of the Libyan plateau along the Nile are 
well illustrated by the views on Introd. PL VII., for which I am indebted to Professor 
Flinders Petrie. The portion of the escarpment defining the Nile Valley in Lower 
Egypt is markedly different from the escarpment at Naquada, below Thebes. In the 
former region, the plateau generally approaches the Nile as low rounded spurs about 
200 metres above sea-level, separated frequently by shallow valleys the floors of which 
are more or le.-s covered with loose stones, or it may be with fragments of shattered 
limestone, with accumulations of drifted sand, here and there, in the hollows. At 
Naquada, on the other hand, the escarpment has a very rugged configuration and rises 
to 500 metres above the sea. It is cut up into ridges separated by deep ravines, some 
of the latter of considerable length and depth, and presenting the appearance, remark- 
able in an almost rainless desert, as if they had recently contained running streams. 
Similar valleys occur throughout the escarpment, but none perhaps having the foregoing 
characters better defined than those of Naquada. Along these valleys vegetation 
generally finds its way and spreads on to the plateau, as has been illustrated by the 
itineraries of the travellers whose observations have been cited. Between the base of 
the escarpments and the alluvium, on both sides of the Nile, there is usually a fore- 
shore, so to speak, of shingly land supporting a straggling and sparse vegetation of 
ordinary desert plants, more or less merging with the vegetation of the alluvium. This 
foreshore, the wide plains that occasionally separate the elevated desert from the Nile, 
the escarpments with their valleys,- and the immediately adjoining surface of the 
plateau are the areas over which animal life is chiefly distributed, so that an enumera- 
tion of the species found on these areas would practically embrace the reptilian fauna 
of the Nile Valley. The annual submergence of the alluvium is the reason why so 
limited a number of species is found on the cultivated area. In the months when the 
fields are devoid of water and the soil is once again nearly dry, a number of lacertine 
genera are temporarily distributed over it, such as Agama, Acanthodactylus, Eremias, 
and Mabnia ; and along with them such genera of snakes as Eryx, Zamenis, Psammoplus, 
Tarbophis, and Naja. Certain mammals also which have their lairs, as a rule, among 
the rocks of the escarpments or on the neighbouring plateau, find a safe shelter and an 
abundant supply of food amid the fields of beans, cereals, and sugar-cane. 
The climate of the narrow area enclosed by the escarpments of the desert defining 
the course of the Nile differs but little from the climate of the great regions immediately 
to the east and west of the river. The rainfall is about the same in all, but in the 
lower part of the valley the climatic conditions of the Mediterranean basin occasionally 
make themselves felt. It cannot be said that the narrow valley is entirely devoid of 
rain, as seasons now and again recur when it falls in places in gentle showers. 
Frequently, however, years may pass without a drop of rain falling, and thus 
vegetation beyond the influence of the Nile floods becomes completely burned up with 
the exception of a few hardy acacia-trees, and consequently many of the small mammals 
die, whilst the larger forms are driven elsewhere in search of food. 
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