354 NATURAL HISTORY OF ARABIA. 



si;sts of granite ; the lower stratum is red ; at the top it is 

 almost white, so as to appear from a distance hke chalk. 

 This arises from the large portion of white felspar 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 httle in their formation. Granite, 

 both of the gray and red species, limestone, and porphyry are 

 the prevailing rocks. Ohud, famous for one of Mohammed's 

 battles, consists of different-coloured granite. 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 spe- 

 cies of granite, with schorl in the place of felspar, accompa- 

 nied 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 green- 

 stone, trap, and porphyry schistus. Although there are some 

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

 accidentally among them, yet, according to Ali Bey, quartz 

 forms in general the principal masses. Their beds are 

 obhque, and in different angles of declination, dipping west- 

 ward from thirty to forty-five degrees. White marble is said 

 to be found in the neighbourhood ; and some travellers sup 

 pose 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 httle 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, schis- 

 tus and basalt predominate, instead of granite. At Kahhme, 

 near Beit el Fakih, Niebuhr saw a hill composed entirely of 

 pentagonal basaltic columns, each about eight inches in diam- 



