Vol. 67.] THE GEOLOGY OF CTRENAICA. 609 



great tract of lowland, extending from Egypt to the south of 

 Cyrenaica through the Oases of Siwa and Aujila, may have sunk at 

 the same time, or it may not have been raised by the Miocene up- 

 lift to the same extent as Cyrenaica. 



The maps of Cyrenaica, as for example that in Dr. Hildebrand's 

 * Cyrenai'ka ' pi. iii, represent the country as descending to the 

 south in two steep steps ; one of these steps is situated 25 miles 

 south of Slonta ; the other is much farther south, and it separates 

 the Libyan Plateau from the lowland of the Wadi Fareg and the 

 Oases of Siwa and Aujila, of which the former certainly and the 

 latter probably are below sea-level. This representation suggests 

 that the southern boundary of Cyrenaica consists of one or 

 two faults, of which at least the southern is connected with the 

 foundering of the Siwa-Anjila depression. The Slonta Arabs, how- 

 ever, assured us that the country passes gradually downwards into 

 the Aujila plain ; and if so, the Aujila district probably did not 

 share the Miocene uplift, which increased gradually northwards. 1 



The predominant dip of the beds in Northern Cyrenaica is north- 

 ward, and this direction continues as far south and west as the Wadi 

 Khumas and Messa. In Central and Southern Cyrenaica the pre- 

 dominant dip is southward, and it is probably the same in South- 

 eastern Cyrenaica. The main dip-slope, due to the Upper Miocene 

 movements, was therefore to the south. The consequent rivers 

 would, therefore, have carried whatever drainage there may have 

 been down the southern slopes of Cyrenaica through the Wadi el 

 Bah westwards to Benghazi, and through the Wadi el Ajara el Ttemla 

 eastwards to the Bay of Bomba. Along the line of our traverse the 

 most conspicuous drainage is to the north, although at Slonta and 

 Silene we crossed streams beginning with a southward course, and 

 the northern margin of the plateau has been notched by numerous 

 gullies cut by obsequent streams. The wadis in Northern Cyrenaica 

 are now deep canons forming the most picturesque features in the 

 scenery. Although some of the limestones, such as the typical rock 

 of the Derna Limestone, are very soft, the cliffs of the wadis are 

 sometimes vertical. These canons, such as the wadi west of Mersa 

 Susa (named by Smith & Porcher the Wadi Lebaiath, but my guide 

 called it the Wadi Dimi-ell), the Wadi Jebrail, and the great 

 Wadi Derna, are so large that they inevitably suggest the question, 

 whether they were not excavated by great perennial rivers, when 

 the country had a better water-supply and heavier rainfall than 

 at present. 2 



1 The evidence of the Arabs (see p. 586) agrees with the conclusion in 

 Dr. Hildebrand's text, op. cit. pp. 151-152: 'We do not yet know how the 

 whole Libyan plateau rises towards the north, whether it rises in terraces, 

 whether it slopes up gently, or whether our Cyrenaica is placed on it like a 

 dome. Only one thing almost all travellers have united in stating, that 

 Cyrenaica gradually sinks to the south and at last loses itself in the Libyan 

 Desert.' 



2 Corresponding to Dr. Blanckenhorn's ' Pluvial Period' in Egypt, 'Neues 

 zur Geologie & Palaontologie iEgyptens — IV. Das Pliocan- & Quartar- 

 zeitalter ' Zeitschr. Deutsch. Geol. Gesellsch. vol. liii (1901) p. 393 & table 

 facing p. 308. 



