576 THE GEOLOGr OF THE NOETHEEN ETBAI. 



42. Notes on the Geology of the Noetheen Etbai. Abridgment of 

 a paper by Eeistest A. Eloyee, Esq., E.L.S., E.G.S. (Eead 

 April 27th, 1892.) 



By the scientific expedition despatched by H.H. the Khedive in the 

 beginning of the year 1891 the whole country between the Eed Sea 

 and the Nile, and between Kos and Kosair on the north and Assuan 

 and Berenice on the south, was examined and mapped out. Close 

 attention was paid to the geology, for a study of which special 

 preparation had been made, and the simplicity with which the 

 formations are arranged enables a fairly correct picture to be drawn 

 of an area of 2300 square miles, although the time given to its 

 examination extended but little over three months. 



The Map which accompanies the present abridgment shows the 

 principal places mentioned in the text, and may be useful to any 

 one who may have time and opportunity to visit the country. 



§ 1. Kin^a-Kosaie-Beeenice. 



The principal feature is a long ridge of igneous rock running 

 N.N.W. and S.S.E. In this ridge, porphyry at times rises up into 

 lofty peaks. These are at Jebel Dukhan, where are the quarries of 

 the ' imperial red porphyry ' now worked by Mr. Brindley, F.G.S. 

 Next southwards come the porphyry peaks of HuUus, and south 

 again the peaks of Jebel Eerayeg, the TretreMnrvXav opos of Ptolemy. 

 Between these peaks the ridge is lower, granites and metamofphic 

 rocks alone appearing. The ridge runs near the sea, and the valleys 

 on the east are short, frequent, and deeply eroded, both from the 

 more frequent rains consequent on the sea-moisture, and from the 

 slopes being steeper on the eastern than on the western flank. 

 West of the watershed are four main drainage-basins, the Zeidun, 

 the Abbad, the Khareit, and the AUaki, which last reaches the Nile 

 some 30 miles south of Assuan. 



These run over a vast bed of sandstone which dips slightly 

 to the west and to the north, when it sinks under limestone.^ 

 What may have been the original thickness of this sandstone it 

 may be possible ^to conjecture from various circumstances which 

 will be hereinafter detailed, but it would seem that there is now no 

 great thickness of it left. 



Under the sandstone comes a bed of blue clay, absent or very 

 thin in the south, and increasing rapidly in thickness northwards. 

 This blue clay may represent the mica-slate of Jebel Zabara and 

 the slate-breccia of the Kina-Kosair road. Under the blue clay 

 comes a grey granitic rock. It is very coarse-grained, and composed 



^ In the latitude of Kosair, on both sides of the watershed, is seen limestone 

 bedded over sandstone over blue clay ; nor was any difference observed in the 

 sandstone or the limestone on either side of the watershed. 



