572 PROE. J. W. GREGORY ON [Nov. I9II, 



18. Contributions to the Geology of Cyrenaica. By Prof. J. W. 

 Gregory and others. (Read March 8th, 1911.) 



[Plates XLII-XLIX.] 



(A) The Geology of Cyrenaica. By John Walter Gregory, 

 D.Sc, F.R.S., F.G.S., Professor of Geology in the University 

 of Glasgow. 



[Plate XLII — Map and Sections.] 



Contents. 



Page 



I. Introduction 572 



II. Field-Observations 578 



(a) The Neighbourhood of Derna. 

 (//) Derna to Cyrene. 



(c) Mersa Susa (Apollonia) to Slonta. 



(d) Slonta to Messa. 



(e) Messa to Merj. 



(f) Merj to Ptolemeta. 

 {g) Merj to Benghazi. 



III. Lists of Fossils 594 



IV. Classification and Correlation of the Cyrenaican Rocks 593 



V. The Tectonic Geology 603 



VI. The Wadis, and Possible Variations in Pleistocene 



Climate 608 



VII. The Composition of the Soils 612 



VIII. Summary of Conclusions 614 



I. Introduction. 



Cyrenaica, a province of Eastern Tripoli, is the projection on the 

 northern coast of Africa between the Gulf of Sidra (the Greater 

 Syrtis) on the west and the Bay of Bomba on the east. The name 

 is sometimes used to include Marmarica and the Libyan coast, as 

 far as the still undetermined western frontier of Egypt ; but the 

 restriction of Cyrenaica to the wide foreland occupied by the famous 

 Greek colony whose capital was Cyrene renders it a more natural 

 geographical division. It is thus equivalent to the Gebel el Akdar — 

 the Green Hills — of Arab nomenclature ; while the Gebel el Akabah 

 — the Abrupt Hills, — its eastward continuation between the Bay of 

 Bomba and the Bay of Salum, 1 is the plateau of Marmarica. 



Cyrenaica, as thus restricted, is a land of great classical interest: 

 it includes the ancient Pentapolis ; the city of Cyrene stood on the 

 northern edge of its plateau ; and the Garden of the Hesperides and 

 the Biver Lethe lay in hollows in the limestone on its coastal plain. 



i The spelling of most of the Egyptian place-names is adoj3ted from the 

 recent map of Egypt published by the Geological Survey of that country. 



