Geology of West-Central Sinai. 83 



Cretaceous and Eocene periods was followed by a geocratic movement 

 in Oligocene times, when the fluvio-marine beds of the Fayum were 

 formed with the remarkable deposits containing mammalian remains 

 at their base. To this succeeded another hydrocratic movement in 

 Miocene times. Miocene deposits occur in northern Egypt, on the 

 borders of the Gulf of Suez, and in the neighbourhood of Has 

 Mohammed. They occur at different levels and sometimes have the 

 character of beach deposits. Did the earlier Miocene deposits 

 advance over a planed down surface of older rocks ? This is 

 suggested by Dr. Ball^s work, for it is impossible to avoid the 

 conclusion that the Cretaceous and Eocene deposits once extended 

 over the whole area. Moreover, a small patch of Miocene strata, 

 wedged in between two faults just north of Gebel Sarbut el Gamal, 

 is represented on the map as resting both on Nubian Sandstone and 

 on Cenomanian, whereas Miocene rests on Campanian, without 

 any intervention of Eocene on the mountain itself, of which it forms 

 the summit. 



As evidence of the great differences of level at which Miocene 

 rocks occur, it may be pointed out that the boring for oil at Gebel 

 Zeit 1 ended at a depth of about 1,100 metres below sea-level in 

 rocks which are supposed to be of Miocene age, whereas the top of 

 Gebel Sarbut el Gamal is 642 metres above the sea, making 

 a difference of 1,742 metres. How far these differences of level are 

 to be accounted for by deposition at different times while geographical 

 evolution was going on, and how far they are due to movements of 

 elevation and depression affecting large areas or to faults subsequent 

 to deposition, cannot be determined with precision at present, but 

 the last-mentioned cause has certainly played an important part. 

 Basalt sills and dykes occur at many points in the district. They 

 are all referred by the author to the Miocene period. 



The ores of manganese and iron (pyrolusite, psilomelane, wad, 

 and haematite) occur at the junction of the Carboniferous Limestone 

 and the underlying sandstone in certain places. They form irregular 

 deposits which are only found in the neighbourhood of faults and 

 become thicker and richer as the faults are approached. Where they 

 occur certain dolomitic limestones, containing small amounts of 

 manganese and iron, have partially or wholly disappeared, and it is 

 suggested that the circulation of water along the fault fissures has 

 removed the carbonates of lime and magnesia from the limestones 

 and left behind the manganese and iron as oxides. The principal 

 objection to this theory is that the amount of manganese in the 

 dolomites which have been analysed is very small — less than ^ per 

 cent. Is it possible that beds much richer in carbonate of 

 manganese, like those occurring in Merionethshire, are present but 

 not exposed ? 



In these days, when there is a marked recrudescence of old 

 superstitions, not confined to geology, it is interesting to note that 

 Dr. Ball, so far as this district is concerned, attributes the surface 

 inequalities directly to erosion. After pointing out that valleys 



1 Explanatory notes to accompany the Geological Map of Egypt by W. F. 

 Hume, Cairo, 1912. 



