352 NATURAL HISTORY OF ARABIA. 



all the tombs and temples of Petra have been excavated. To 

 the southward it follows the whole extent of the great valley. 

 The summits of these cliffs are so irregular and grotesque, 

 that when seen from a distance they have the appearance of 

 volcanic mountains. Their naked perpendicular sides pre- 

 sent calcareous rocks, sandstone, and flint lying over each 

 other in horizontal layers. In several parts of the caravan- 

 route between Suez and Akaba, Burckhardt observed large 

 insulated masses of porous tufwacke. The famous Gebel 

 Mokkateb, or "Written Mountain, is of sandstone ; but at 

 Wady Borak the formation changes to porphyry, alternating 

 with strata of greenstone. 



The peninsula of Sinai exhibits a considerable diversity of 

 structures, differing in their ingredients from the ridges in 

 other parts of Arabia. On approaching the central summits 

 of the Sinai group, the traveller encounters abrupt cliffs of 

 granite from 600 to 800 feet in height, whose surface is 

 blackened by the sun. These precipices enclose the Holy 

 Mountain on three sides, leaving for a passage a narrow defile 

 about forty feet in breadth. The upper nucleus, including 

 the rugged peaks of St. Catherine, is composed almost entirely 

 of granite. Among the lower ridges porph\T)' and green- 

 stone begin to appear. In many places the latter takes the 

 nature of slate. The layers of the former are sometimes 

 verj' striking, running perpendicularly from the top to the 

 base of the mountain in strata of about twelve feet in width, 

 and projecting slightly from the other rocks. The porphyry 

 of Sinai, Burckhardt rem.arks, is usually a red indurated ar- 

 gillaceous substance. Some specimens had the appearance 

 of red felspar. In the argil are imbedded small cr^'stals of 

 hornblende or of mica, and thin pieces of quartz, the colour 

 of which is universally red. The granite is gray and of the 

 small-grained species, of which the Towara tribes manufac- 

 ture hand-mills, which they dispose of to the northern Arabs, 

 or export for sale. The intervening valleys are interspersed 

 with blocks of chalk- rock ; on each side, beds of red or white 

 sandstone present their smooth perpendicular surface. 



Shaw remarks, that on the route between Cairo and Suez 

 an infinite number of flints and pebbles are to be met with, 

 all of them superior to the Florentine marble, and frequently 

 equal to the Mocha stone in the variety of their figures and 

 representations, having the images of little trees, shrubs, or 



