Vol. 67.] THE GEOLOGY OF CYRENAICA. 581 



form a small hill between the path and the shore. This chert- 

 bearing rock is also well exposed in the banks of the Wadi Nagr, 

 where it is represented by a soft chalk-like limestone with lines 

 of flat chert-nodules, dipping 5° northwards. This chert-bearing 

 limestone extends along the foot of the cliffs, to the west of our 

 camp. 



West of the wadi, Dr. Trotter collected a fossil which Mr. Newton 

 has determined as Lucina cf. noJcbahensis Oppenh., in a limestone 

 free from Nummulites. Tf this specimen were in situ, then, as at 

 Bint, east of Derna, Upper Eocene rocks are faulted down at the 

 foot of the plateau-scarp. 



Tig. 2. — Section in the plateau-face at Wadi Nagr, 

 west of Derna. 



S. 



Brown Limestone 



Ltthothamnron Lim csfflnn 



N. 



Feet 

 -iooo 



8oo 



White Derna 



Limestone with 



Nummulites gizeliensis 



Chalky limestone with chert-nodules 



Sea-level 



The sequence of the rocks in this district may be observed in the 

 ascent of the Okbah or Aukubah, the Arab name for the cliff which 

 forms the northern face of the plateau. The rocks are well exposed 

 there, except that some bands are covered by an efflorescent lime- 

 stone-crust. The chalky chert-bearing limestone passes gradually 

 up into a harder limestone with chert-nodules, which is succeeded 

 by the cream-coloured N.-curvispira Limestone : this, being very 

 soft, has been carved into caves, and is in places overhung by the 

 rock above. At about 500 feet above sea-level the slope becomes 

 steeper, up a cliff of the brown-weathering limestones (the Slonta 

 Limestones), which begin with a layer of limestone full of small 

 foraminifera, succeeded by a white limestone with Orthophragmina 

 pratti and Operculina, which continues up to the height of about 

 630 feet. It is succeeded by a pinkish limestone, 30 feet thick, 

 containing nullipores and some foraminifera, among which Mr. 

 Chapman has identified Nummulites curvispira and Truncatulina ; 

 so he refers the brown limestones to the Middle Eocene. At 660 

 feet is a band of white marl, followed by the typical brown-weather- 

 ing limestone, which continues to the edge of the plateau at about 

 750 feet. (See fig. 2, above.) 



