396 



NATURAL HISTORY OF ARABIA. 



chalk. This arises from the large portion of white fel- 

 spar in it, and the minute particles of hornblende and 

 mica. Towards the middle of the mountain and between 

 the granite rocks are broad strata of brittle black slate, 

 mixed with layers of quartz, felspar, and micaceous 

 schistus. The quartz includes thin strata of mica of the 

 most brilliant white colour, which is quite dazzling in 

 the sun, and forms a striking contrast with the blackened 

 surface of the slate and the red granite. 



The hills that branch off from this great chain between 

 Medina and Mecca differ little in their formation. Gra- 

 nite, both of the gray and red species, limestone, and por- 

 phyry, are the prevailing rocks. Ohud, famous for one 

 of Mohammed's battles, consists of different-coloured gra- 

 nite. On its sides Burckhardt found flint, but no lava. 

 Its entire extent from west to east is about four miles. 

 The lowest range above Jidda, which is seldom more 

 than 400 or 500 feet high, is calcareous ; but the rock 

 soon changes into gneiss and a species of granite, with 

 schorl in the place of felspar, accompanied by masses of 

 quartz and some mica. This formation continues with 

 little variety as far as the vicinity of Gebel Nour, near 

 Mecca, where granite begins. The mountains enclosing 

 the valley of Muna are composed of variously-coloured 

 granite, mixed in a few places with strata of greenstone, 

 trap, and porphyry schistus. Although there are some 

 beds of hornblende, felspar, mica, and schorl, to be found 

 accidentally among them ; yet, according to AH Bey, 

 quartz forms in general the principal masses. Their beds 

 are oblique, and in different angles of declination, dip- 

 ping westward from thirty to forty-five degrees. White 

 marble is said to be found in the neighbourhood ; and 

 some travellers suppose that there is abundance of valuable 

 minerals, which are only hid because the inhabitants want 

 skill or enterprise to discover them. 



The geological description of the country northward of 

 Hejaz applies, with little variation, to the lofty chain that 

 extends along the coast for nearly 1800 miles, from Mecca 

 to Muscat; except that, in the ridge behind Tehama, 

 schistus and basalt predominate, instead of granite. At 

 Kahhme, near Beit el Fakih, Niebuhr saw a hill com- 

 posed entirely of pentagonal basaltic columns, each about 

 eight inches in diameter, and so uniformly regular, that 

 they might be mistaken for the work of art. They rise 

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