THE GEOLOGY OF SINAI. 
19 
which gives them a peculiar castellated appearance. The strati- 
fication of this sandstone appears always to be perfectly hori- 
zontal, and there can therefore he little doubt that it was 
deposited after the upheaval of the igneous rocks; an addi- 
tional proof that this was the case is also afforded by the 
absence of change in the nature of the sandstone, whenever it 
is found in close proximity to the granite. An equal absence 
of change is also to be observed where the limestone occurs in 
contact with the same rocks. The limestone apparently was 
deposited previously to the sandstone ; an enormous denudation, 
however, must have taken place before the deposition of the 
latter ; for masses of limestone, showing no signs of upheaval, 
occasionally occur at a much higher level than the sandstone ; 
the thickness of the stratum of sandstone which was subse- 
quently deposited must have exceeded 2,000 feet. Whether 
the denudation that has since taken place has been caused by ter- 
restrial or marine agency, is a question that has yet to be solved. 
Considerable masses of sandstone occurring which contain a 
large percentage of calcareous matter render it probable that that 
rock was in process of formation while the limestone was still 
undergoing disintegration. Some slight upheaval of the igneous 
rocks appears to have taken place between the deposition of the 
limestone and the sandstone rocks, since the stratification of the 
former occasionally appears slightly disturbed, while that of the 
latter, which rests upon it, retains its horizontal position ; but 
this upheaval must have been very gradual and local. The 
only traces of active volcanic agency which are now to be found 
in the peninsula are the boiling sulphur-springs and hot caves 
of Jebel Hummam, the traditional baths of King Pharoah, and 
two warm springs which burst from the foot of a hill a little to 
the north of Tor, and are held in great repute by the Arabs 
for their medicinal powers. 
The sandstone formation is especially interesting, as having 
formed the great mining district of the ancient Egyptians in 
Sinai, as is attested by the numerous tablets of hieroglyphics 
which are found at Wady Mughara, and Serabit-el-Kadim. The 
aspect of the sandstone mountains is very different to that of the 
limestone and granite mountains. The limestone mountains 
present a tubular summit and steep sloping sides ; the granite 
mountains may be recognised almost at any distance by their 
bold jagged peaks ; the sandstone mountains form with their 
sides a series of steps, and are frequently pyramidal in shape. 
The sandstone is generally of a reddish ferruginous colour, 
though its surface is for the most part covered with a dark 
brown oxide of iron, which is apparently formed by the decom- 
position of the rock. The Egyptian mines which have as yet 
been discovered are all turquoise mines, with the exception, 
VOL. VI. —NO. XXII. I) 
