PHYSICAL ASPECTS OF ADEN. 
27 
materials. The rock encloses numerous shells and corals of species 
existing in the Arabian Sea. 1 
As to the origin and age of the two peninsulas, there are only a few 
facts which may serve as a basis for further conclusions. 
Although our geological knowledge of Arabia is lamentably deficient, 
we know from the researches of Carter and Blanford in the south, and 
from the observations of Blunt and others in the north, that Arabia 
must be considered as the eastern portion of the great Saharan desert 
plateau. As in the Egyptian deserts, the basis of the country consists 
of crystalline rocks, overlain by horizontal sedimentary formations of 
Cretaceous and Eocene age. 2 If Arabia may be regarded geologically 
as part of the African plateau, it is evident that the Bed Sea must have 
been formed by subsidence of the country in comparatively recent times, 
with great probability at the beginning of the Middle Pliocene*, 
Whether the formation of the volcanoes in Aden and along the coast 
between Tair and Perim was immediately connected with the disappear- 
ance of that vast stretch of firm land, or whether it dates back to a more 
recent terrestrial convulsion, is difficult to decide from the scanty 
geological data we possess regarding the countries of the Red Sea. 3 
On leaving Aden we come on a low-lying sandy plain, on which 
generally nothing but a small scrubby bush will grow. The water 
which is to be met with at a depth below the surface varying from 3 to 
about 18 feet throughout this^tract, is directly influenced by the rise and 
fall of tide. It is, of course, brackish to a degree, being in fact almost, 
if not quite, simple sea-water. This tract of sand extends nearly to 
Shaikh Othman north, and skirts the foreshore of Aden Bay and the coast- 
line eastward, as far as El Konis, extending inland in a belt of varying 
thickness, sometimes running right up into the sand-drift, at others only 
a few hundred yards from the sea-coast. 
Between this salt belt and the hills is an alluvial plain falling from 
the hills towards the sea, with a slope near the foot of the hills of about 
30 feet in a mile, easing off to about 17 feet in a mile, till it reaches 
the salt belt, which is very nearly dead level. The soil of this part of 
the country is composed of a sandy clay, very retentive of moisture, and 
capable of high cultivation. Throughout this alluvial tract of country 
a slightly brackish, but drinkable water, is met with at a depth of from 
60-70 feet. The water-bearing stratum seems nearly parallel to the 
1 Burr, F. : 1. c., p. 84. 
2 Geographical Journal, Yol. 32 (1908), p. 568. 
8 Suess, E. : Das Antlitz der Erde. I, p. 474. 
Lapparent, A. dc. : Geographie Physique. Paris, 1896, p. 528. 
