18 
rOPULAll SCIENCE REVIEW. 
of stones and rubble generally fills the lower portion of their 
beds, and under this the water flows unseen, except in times of 
floods, or when, as in Wady Feiran, or in Wady Hibran, it is 
forced to the surface by rocky barriers narrowing and contracting 
their courses. It is not, however, till one wanders over the 
mountain on foot, or visits the Arab encampments towards even- 
ing, and sees the bundles of herbs which the men and children 
bring home for the camels and goats, that one can form any just 
estimation of the amount of vegetation which the rocks conceal. 
The mere passer-by also is apt to overlook the quantity of 
pasturage afforded by many of the wadies; this evidently 
varies much, according to the season of the year, and the 
amount of rain which falls in the winter months, and it is 
sometimes increased in an almost miraculous manner by the 
heavy rains accompanying thunderstorms at other times. 
So far I have spoken only of the rocks of this central district 
under the general term “ granitic I will now endeavour to 
describe their geological features more accurately. They appear 
to be principally composed of syenite, especially in the more 
elevated districts, such as Mount St. Catharine, Jebel Musa, and 
Jebel Serbal ; but hornblendic, quartzose, and porphyritic rocks 
are not uncommon. The mountains are frequently seamed from 
top to bottom with veins of porphyry, greenstone, and basalt, 
which gives them a peculiar striped appearance, and adds much 
to their beauty. This is especially remarkable on the east of the 
well-known Wady Mokatteb, and in some of the wadies on the 
road between Jebel Musa and Akaba. Felspar and porphyry 
occur largely near Ras Mohammed, and gneiss and mica-schist 
are found in the neighbourhood of Wady Mokatteb. The rock of 
Moses, which lies in the Wady Leja, near Jebel Musa, and 
which tradition says followed the Children of Israel in their 
wanderings through the desert, is a mass of granite, with 
crystals of white and pink felspar and quartz, across which 
runs diagonally a vein of pure felspar, containing ten or 
twelve cracks in its surface, which are said to be the mouths 
from which the water flowed for the different tribes. This 
rock is exactly fourteen feet in height and seventeen feet in 
breadth at its broadest part. The veins which seam the moun- 
tains have frequently been described as rich in metallic ores. 
This appears, however, to be a mistake. Cretaceous limestone, 
with numerous bands of flints, occurs in large masses in the 
north-west of the Tur district, in conjunction with sand- 
stone, and also on the north-west of Jebel Serbal : at the latter 
spot nummulitic limestone also occurs ; near Tor and Ras Mo- 
hammed a limestone of a more recent formation is found. 
In several parts of the peninsula the granitic mountains are 
capped by a stratum of sandstone of considerable thickness. 
