Vol. 67.] THE GEOLOGY OF CTRENAICA. 589 



yielding the large Nummulites curvispira. The track from Bigratah 

 to the plain of Merj crosses a low pass at the height of 1120 feet 

 above sea-level, where the chert-bearing limestones crop out from 

 beneath the Derna Limestones. 



The plain of Merj is an alluvial plain exceeding 50 square miles 

 in area ; it is bounded on the south-east by an escarpment of the 

 Derna Limestone resting upon the chert-bearing limestone. The 

 town of Merj (generally regarded as the ancient Barca 1 ) is situated 

 on a small rise, due to the outcrop of a Priabonian limestone. 

 The plain is bounded on the south-east by a long straight cliff, 

 which has a trend of 52°, and is continued south-westwards along 

 the plain of Silene. This long scarp is formed mainly of Derna 

 Limestone : the cherty limestone is exposed beneath that rock in 

 the north-eastern part of the scarp, near Bigratah. The beds are 

 here dipping south-westwards so that the chert-bearing limestone 

 disappears below the surface ; the beds then become horizontal, 

 and then dip south-westwards to a low syncline, of which the axis 

 meets the scarp south-south-east from Merj. Some 5 miles south- 

 west is another low anticline ; it is followed by another syncline, 

 and the dip continues to the north-east as far as the wide breach 

 in the fault-scarp made by the Wadi Jebril. So far as I could tell 

 from a distant view, the beds again dip south-westwards, become 

 horizontal, and then the scarp becomes quite low. A higher 

 scarp could be seen behind it, and, judging by its white face, it 

 may also be formed of Derna Limestone. 



The long cliff that forms the south-eastern boundary of the 

 plains of Merj and Silene has the aspect of a fault-scarp, for it is 

 remarkably straight in direction ; the only projections from it are 

 talus-fans opposite the wadis ; there are no spurs or outliers, such 

 as would be expected in an escarpment due to denudation ; and its 

 course is not affected by the changes of dip in the limestone. 



That this hill-line is a fault-scarp is also shown by the palaeonto- 

 logical evidence. The limestone at the wells of Merj contains 

 Pecten arcuatus Brocchi, Lacina cf. pharaonis Bellardi, and Vulsella 

 crispata Fischer, and, according to Mr. Newton's determinations, is 

 therefore Priabonian. The characteristic nummulite of the Wells 

 of Merj is identified by Mr. Chapman as N. rjizehensis var. lyelli, 

 whereas the species in the cream-coloured limestone of the Merj 

 scarp is iV. gizehensis typica. Hence the evidence of the foramini- 

 fera agrees with that of the mollusca, that the limestones at Merj, 

 which occur at levels ranging from 835 to 850 feet, belong to a 

 higher horizon than the limestone at the level of 1000 to 1240 feet 

 in the hills. 2 miles south of the town. 



1 Barca, however, was at Ptoletneta, according to Smith & Porcher, ' History 

 of the Eecent Discoveries at Cyrene ' 1864, p. 4, and Gr. Dennis, ' On Recent 

 Excavations in the Greek Cemeteries of the Cyrenaica ' Trans. R. Soc. Lit. 

 ser. 2, vol. ix (1870) pp. 141, 156. 



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