Mr. Doughty on the Geology of Arabia. 325 



the rocks need not be referred to the introduction of any intrusive 

 rock, but to a more general agency, namely, that which produced 

 the ancient axis of elevation off the east coast of Cornwall, in the 

 line of the Eddystone, and parallel to the general granitic axis of 

 the Cornish peninsula. 



2. " Outline of the Geology of Arabia." By C. M. Doughty, Esq. 

 Communicated by Prof. T. G. Bonney, D.Sc, E.R.S., Sec. G.S. 



The author described the general outline of the geology of a 

 considerable district in the western part of Arabia, over which he 

 had travelled. It was not in his power to enter into details, espe- 

 cially as regarded the sedimentary rocks, because the circumstances 

 under which his journey was undertaken made it impossible to 

 bring back specimens. There was, however, considerable simpli- 

 city in the geological structure of the country. The igneous rocks 

 consisted of granites and basalts, the latter breaking through the 

 former. The sedimentary rocks, which are newer than the granites 

 and, in fact, rest upon them, consist of — 



(a) A yellowish sandstone, with stains of a reddish or greenish 

 colour and veins of ironstone. In this, for example, the rock- 

 tombs <kc. of Petra have been excavated. These sandstones, in the 

 author's opinion, may be traced as far as Medina, and occur all 

 about Kasim. They often weather in a singular way ; pebbles are 

 scarce in them ; fossils he had not seen. 



(b) The limestone contains bands of flint, and appears to be 

 identical with that which occurs in Palestine, and is, he thinks, 

 probably of Cretaceous age. 



(c) Of much later date is a coarse flat gravel which overspreads 

 a considerable tract of country, as, for example, at Mount Seir in 

 Edom, altogether about 250 square miles. The flints are doubtless 

 derived from the limestone, and are often polished by drifting sand. 

 It occurs on plateaux at very considerable elevations above the sea, 

 sometimes forming the highest ground in the neighbourhood ; and 

 sections had shown this gravel to be more than 20 feet deep. In 

 it the author had discovered two or three flint weapons of palaeo- 

 lithic type, rude, but very like those of Hoxne or St. Acheul. 



The granite by its aspect and mode of occurrence recalls that of 

 Sinai. It is cut by dykes of basalt ; now and then the author had 

 observed other intrusive igneous rocks, which he must be content to 

 classify as traps. The dykes of basalt, however, were not the only 

 modes of occurrence of this rock; there were considerable flows of 

 basaltic lavas and occasional small craters. These volcanic districts 

 bear the name of Harra ; the principal are the Aneyrid, the Khay- 

 bar, and the Kesshub. The last lies between JN'ejd Arabia and the 

 Mecca country. These masses of lava &c. are comparatively modern ; 

 eruption, indeed, has in one or two localities occurred in historic 

 times, and steam has been seen to issue from certain craters. 



