Vol. 67.] THE GEOLOGY OF CYEENAICA. 603 



but I only remember finding quartz-pebbles once, and sand-grains in 

 the limestone are rare. Some of the limestones are argillaceous, or 

 include layers of marl ; and this material is composed of a very tine 

 clay. We saw no representatives of the terrestrial and freshwater 

 deposits of Egypt, or of the abundant sandstones and clays found 

 in the corresponding rocks of Tunisia. 



The Cyrenaican limestones must have been deposited mainly in 

 water of moderate depth. The rocks which indicate the deepest 

 water are the fine-grained chalky Globigerina Limestones, which 

 form the upper part of the Apollonia Limestones, west of Ptolemeta, 

 and are also exposed at the Wadi Nag'r. During the deposition of 

 the Slouta Series the sea was shallower near Slonta than at Cyrene, 

 for clastic material becomes more abundant as the beds are traced 

 south wards ; hence land doubtless existed in that direction, and 

 if no considerable river discharged on that coast it need not have 

 been far away. The widespread coral-reef limestones near the 

 top of the Slonta Series indicate a shallowing of the sea, and the 

 area may have been raised above sea-level daring Lower Oligocene 

 times ; for the Slonta Series of Priabonian age is apparently suc- 

 ceeded by Aquitanian limestones. 



Another gap succeeded the Aquitanian ; for the next beds are 

 shallow-water Middle Miocene limestones, which are widely deve- 

 loped on the coastal plains east of Benghazi, and are preserved in 

 occasional fragments on the summit of the Cyrenaican plateau. 



The Cyrenaican sequence resembles the Maltese in the persistence 

 of marine conditions. The Maltese beds, however, began later, 

 as the oldest is Tongrian, while the latest is Tortonian. The 

 Globigerina Limestones of Malta were probably laid down in 

 deeper sea — Sir John Murray's estimate for them is 1000 fathoms — 

 than any in Cyrenaica ; but the chalky limestones of the Apollonia 

 Series were probably formed in water not much shallower. The 

 long continuity of a variable marine series is a feature 

 common to the geology of both Malta and Cyrenaica. 



V. The Tectonic Geology. 



The two essential facts in the structural geology of Cyrenaica 

 are, that pre-Kainozoic rocks are unknown there i ; and that all its 

 rocks are marine limestones, which, although raised in places to 

 2500 feet above sea-level, are, except in the vicinity of the main fault, 

 still horizontal or inclined in broad shallow folds. The country, 

 therefore, has no resemblance either in composition or in structure 

 to the Atlas Mountains. It is essentially a block of Eocene 

 Limestone, capped by some outliers of Oligocene and 

 Miocene, and flanked by Pleistocene. The Eocene rocks, 

 which form the great mass of the country, resemble those of Egypt ; 

 but I saw no representative of the Bartonian and Oligocene terres- 

 trial deposits found in Egypt, as in the Eayum. 



1 The most likely position for Cretaceous rocks is on the lower part of the 

 Tokra scarp. 



Q.J.G. S. No. 268. 2t 



