Vol. 67.] THE GEOLOGY OF CYRENAICA. 601 



The Nummulites and Operculina libyca, which lived from the 

 Lower Libyan to the Miocene, have therefore a somewhat variable 

 range in age, and their distribution must be influenced by bathy- 

 metric conditions. 



Above the Priabonian or Upper Eocene rocks of Cyrenaica there 

 appears to be a gap in the succession, as the next beds recognized 

 belong to the Upper Oligocene or Aquitanian. The limestones of 

 Wadi Umzigga and Birlibah contain Lepidocyclina elephantina, 

 which Mr. Chapman assigns to the Middle or Upper Oligocene 

 (Stampian or Aquitanian); the mollusca from the same limestone 

 are identified by Mr. Newton as Aquitanian : hence the rocks may 

 be accepted as Aquitanian. They are, therefore, of nearly the same 

 age as the limestones at Cyrene, which are the best representatives 

 in Cyrenaica of the Aquitanian Series. 



At Gubah, west of Wadi Umzigga, the rocks are Miocene, and 

 probably Helvetian ; and as I found an Echinoid of that age near 

 Birlibah, there are apparently Miocene outliers on the Lepidocyclina 

 Limestones. 



The Miocene rocks were not once seen resting directly upon the 

 older rocks. They form the plains at the foot of the Tokra scarp, 

 east of Benghazi ; but there they have been faulted down against 

 the Lower Eocene beds. Some shelly limestones, from which 

 Mr. Newton has identified the Miocene Anadara turonica, occur on 

 the divide between the plain of Merj and the wadis leading to the 

 coast near Ptolemeta. They lie upon the Apollonia Limestone. 

 The Gubah Limestones are also probably faulted down against the 

 rock which forms the plateau near Zawiah Charrah ; but we 

 obtained no definite evidence as to their relations, as we had been 

 asked to travel quickty and with special care to avoid arousing 

 suspicion during that stage of the journey. 



The sequence of rocks in Cyrenaica is, therefore, more varied 

 and complex than was anticipated. The Miocene rocks, instead 

 of occupying the whole country, are sparsely represented, and 

 Cyrenaica consists essentially of a vast block of 

 Eocene limestone. This rock is capped by some outliers of 

 Oligocene and Miocene; while some Miocene limestones have 

 been faulted against its western foot, and it is fringed by low- 

 level, marine, Pleistocene limestones. 



The suggested classification and correlation of the Cyrenaican 

 beds and their relations to those of Egypt, Tunis, and Malta, are 

 shown in the table on p. 602. 



The stratigraphical succession in Cyrenaica differs, therefore, 

 from that in Egypt and Tunisia, owing to the continuity of the 

 marine rocks in Cyrenaica and their deposition farther from land. 

 The most striking feature in their lithology is the paucity in 

 mechanically-derived sediment — a fact brought out clearly by a 

 careful study of a series of microscopic sections made by Mr. D. P. 

 Macdonald. The series must include nearly 3000 feet of strata, 

 which consist of limestones almost entirely composed of organically 

 formed material. There are occasional beds of limestone-breccia. 



