578 THE GEOLOGY OP THE NORTHEEN ETBAI. 



of ' Stonehenge' given them by the Expedition. Here, at 1550 feet 

 above sea-level, is the edge of the sandstone-plain. The ' cataract ' 

 rock swells and bulges up through the rapidly-thinning metamor- 

 phosed edge of the sandstone. 



The Mikbia ' divide ' is the * cataract ' formation, rising at a 

 gradually increasing angle, till at 2450 feet it is perpendicular, 

 following the Wadi Mikbia to the east, the line passes through a 

 great variety of vertical schists, and finally a plain of ' cataract ' 

 rock slopes right down to the sea, where, just at the edge, are two 

 recent sandstone and limestone banks, and, in the sea itself, coral 

 supporting mangrove forests. 



Abu Gurdi is a huge truncated cone of compact granite which 

 deflects the eastward drainage to the north. It is surrounded by 

 vertical schists and a mass of schistose rocks in thin layers inclined 

 at every angle with the horizon. But seawards these schists give 

 way to ' cataract ' rock. East of the watershed for 60 miles to the 

 north, ' cataract ' rock, with ridges of vertical schists and a narrow 

 fringe of recent limestones and sandstones, is a brief geological 

 description of the country. 



§ 3. The "Wadi Jemal Area. 



The catchment-basin of the "Wadi Jemal is the next matter for 

 description. Approaching from the sea the tall porphyry peaks of 

 Hullus, the cliff is seen to rise steeply for 2000 feet and abruptly 

 for 1000 feet more. Climbing (if it were possible) over these peaks, 

 which rise to a height of 4500 feet, the traveller drops into a deep 

 ravine running north-west, at the source of which are, since many 

 generations of mankind, the broad shady trees and well-fed cattle of 

 the patriarchs Abdullah and Xoraim. 



From east to west the ridge is only six miles across, and the descent 

 from the western cliff by the Helgeit Pass is but little less steep than 

 the eastern cliff. The ridge of igneous rock is, as has been said, 

 hollow-backed between the porphyry peaks. The Arab simile is apt, 

 • — a camel-saddle. At Hullus, in the little craggy ravine from which 

 arises the "Wadi Jemal, are some highly picturesque caverns and clefts 

 in the rugged cliffs. 



The "Wadi Jemal, a fissure between the porphyry on the east and 

 the metamorphosed sandstone-edge on the west, runs north-west for 

 the first six miles, curving round the broad base of the granite peak 

 of Hamata, known in a.d. 800 as the ' Karkashenda,' the huge 

 mountain south of the Emerald Mines. It is here (in the "Wadi 

 Jemal) that sandstone metamorphosis can be seen in every stage. 

 The "Wadi Hullus, which becomes the Jemal in its lower course, 

 bends to the west after running twenty miles. But the traveller 

 mounts to his right (the porphyry wall has long disappeared) over a 

 low ' divide' and enters the "Wadi Durunkat, which forms a chord of 

 the arc of the Jemal, into which it falls in latitude 24° 35' IST. Here 

 it meets the Nugrus, Hafafit, and Sikait coming from the north-west, 

 and all form a fine well-timbered valley, which has carried so much 



