Notices of Memoirs — The Oilfields of Egypt. 317 



be less than 3,000 and may be as much as 6,000 feet. Above this 

 great saliferous formation, which is generally unfossiliferous, occur 

 oyster beds containing Ostrcea virleti and an oyster of the crassissima 

 type. Pending a more detailed examination of tbe palseontological 

 evidence the beds from the flint-conglomerate up to and including the 

 oyster beds are grouped together as being of Plio-Mioeene age. They 

 all belong to the Mediterranean area and can be connected up to the 

 north with the Miocene deposits which occur between Suez and 

 Cairo. 



The oyster-beds are followed by strata containing the remains of 

 sea-urchins and Pectens now living in the Red Sea and Indian Ocean, 

 together with some forms which are apparently extinct. These 

 deposits are referred to as Plio-Pleistocene. They mark the invasion 

 of what had hitherto been a southward extension of the Medi- 

 terranean province by Erythraean forms of life. The plains are 

 largely covered by thick deposits of gravel, derived from the waste 

 of the hills. These are classed as recent, together with a raised 

 beach of corals and molluscs now living in the Red Sea. The beach 

 forms a marked feature on the Zeit and Jemsa coast at an average 

 height of 15 metres. 



Let us now consider the great saliferous formation, with which 

 the oil appears to be associated, in greater detail. Gypsum is the 

 most prominent rock at the surface. Salt in thick beds is only known 

 from the borings. The gypsum is interbedded with clays or marls, 

 and in some places, as in the Jemsa peninsula, with dolomitic lime- 

 stone. Vertical sections of four borings are given. They show 

 remarkable changes within short distances. Bore 11 passed through 

 alternations of gypsum and clays to a depth of about 500 feet ; 

 then through thick beds of salt, separated by thin beds of clay, 

 limestone, and gypsum, to a depth of 2,650 feet, where it ended in 

 salt. The total thickness of salt in this section was found to be 

 about 1,900 feet, or 600 metres. Bore 1, which was apparently 

 situated about one kilometre from Bore 11, is represented as being 

 entirely in limestone. It reached a depth of 1,300 feet. The other 

 two bores, less than 300 metres from Bore 1, were in gypsum, with 

 thin beds of clay and limestone. Speaking of the Jemsa oilfield, 

 Dr. Hume says: "Sections have been made of the area so as to 

 include the bore-profiles, but efforts to explain the present conditions 

 either as simple anticlines or synclines have ended in complete 

 failure. There is a provoking horizontality in the strata of the 

 eastern hill of Jemsa, immediately above the oil-belt on the east 

 coast. . . . What we do know is that the Jemsa borings which have 

 yielded profitable oil occupy a long thin band close to the sea, 

 parallel to the general fold movement of the country." 



The oil at Jemsa appears to have been obtained from the dolomitic 

 limestone which is porous, and therefore likely to form a good 

 reservoir rock. Fragments of a similar limestone are common on 

 the surface of the gypsum throughout the oilfield region. Dr. Hume 

 suggests that this feature, and also the great thickness of limestone 

 met with in some of the borings, may be due to the removal of 

 gypsum in solution from beds containing both carbonate and sulphate 



