Vol. 67.] THE GEOLOGY OF CYRENAICA. 605 



rises in the Wadi Khumas to the height of nearly 1800 feet, and 

 its base is from 1000 to 1100 feet above sea-level near the plain of 

 Merj. The main dip is, therefore, from Western Cyrenaica east- 

 wards into Egypt; hence the Cyrenaican plateau may be regarded as 

 the western limb of the Egyptian geosyneline, of which the centre 

 is occupied by the Oiigocene basin on the west of the Eayum. 



In Cyrenaica, faults are more important than folds. 

 That some of the main geographical features of the country were 

 due to faulting was suggested by Spratt. 1 He attributed the sharp 

 bends of the coast, as at Ras el Tin, the Syrtis, and the Bay of Salum, 

 as also the variations in the level of the plateau, to the influence 

 of faults. This suggestion was repeated by Dr. Hildebrand 2 in 1904. 

 The general aspect of the country, as seen from the sea, appeared 

 consistent with this hypothesis, which was confirmed by the facts 

 discovered during our march. 



The faulting happened so long ago that the actual faults are 

 hidden ; for the scarps have been worn back, and the fault-lines 

 covered by talus. The existence of the faults was, however, proved 

 east of Benghazi and near Merj, for in both cases younger rocks 

 have been lowered against older members of the Cyrenaican sequence. 

 The Gubah Limestones have probably also been faulted down against 

 the Eocene limestones. 



I expected to find that the step-like descent from Cyrene to the 

 coast was due to two parallel step-faults, the upper cliff at Cyrene 

 being the scarp of one of them. The upper cliff is, however, an 

 escarpment. The platform at its foot is not a repetition of the 

 rock (the Cyrene Limestone) of the upper plateau, but an outcrop 

 of an older, harder limestone, which has resisted denudation. The 

 lower cliff, however, if we judge from the evidence collected near 

 Mersa Susa, is doubtless a fault-scarp; for Mr. Newton has identified 

 the fossils collected on the coastal plain at the foot of the cliff 

 (for list, see p. 597) as Priabonian in age, and they are lying 

 at the foot of cliffs of Lower Eocene chert. 



The faults of which I obtained definite evidence may be classified 

 into three main groups, the relations of which are shown in fig. 1 

 (PI. XLII) & text-fig. 4 (p. 604). 



The first group trends approximately east and west, and forms 

 the scarps seen from the sea behind Mersa Susa, and near Derna. 

 In both cases the evidence for the existence of the fault rests on 

 the identification of the Priabonian limestones at the foot of the 

 cliffs, and lying against the Lower Eocene rocks. It appears 

 probable that the coast-line east of Has al Hilil may be due to the 

 same fault ; and it appears natural to suggest that the long straight 

 lines of the coast in Marmarica, and of the north and south sides 

 of Crete, may also have been determined by faults with the same 

 general trend. (See map, fig. 4.) 



The fault east of Derna, which appears to determine the position 



1 T. A. B. Spratt, ' Travels & Besearches in Crete ' vol. ii (1865) App. iv, 

 pp. 375-76. 



2 G-. Hildebrand, ' Cyrena'ika als Gebiet kiinftiger Besiedelung ' 1904, p. 7. 



2t2 



