﻿Vol. 6 1.] CRETACEOUS SYSTEMS OF THE NILE VALLEY. 669 



equivalent of the White Chalk of the oases. The limestones appear 

 to be conformable to the underlying clays, which may themselves 

 form the continuation of the foliated argillaceous beds described 

 above. 



A little farther down stream, notably at Jebel Mayahi, near Ra- 

 ghama, on the right bank, the same marls and limestones (although 

 here the echinids and sponges were not noticed) are only separated 

 from highly-fossiliferous nummulitic and Operculina-Limestones, of 

 Lower Eocene age, by an 8-metre (26J-feet) band of clays. 1 The 

 Eocene limestone is much broken up, but the size and position of 

 the blocks preclude the possibility of their having been transported. 

 In all probability, they represent the remains of a once far more 

 extensive bed, which has been broken up and lowered by the 

 removal of the soft, easily-disintegrated clays below. 2 With the 

 masses of displaced Eocene limestone are huge angular boulders, 

 in a conglomerate of smaller fragments, largely mixed up with 

 pulverized clays from below. When the Pleistocene lake stood at 

 this level, the clays would have been easily removed, and the lime- 

 stones let down and partly broken up by the action of currents 

 and shore-waves. 



A short distance farther north, nearly opposite Eares, a ridge 

 trending eastwards from the river-bank is covered with big blocks 

 of Eocene limestone. The surfaces of the limestone show vermicular 

 sand-etching, and are pierced by numerous holes ; the latter seem 

 to be cavities left by the weathering-out of fossils, rather than to 

 be the work of boring mollusca, for which they might easily be 

 mistaken. In this locality the intervening clays appear to have 

 been entirely removed, the Eocene limestone lying almost directly 

 upon a white, shaly marly limestone. No fossils were collected in 

 the underlying rock, which, although closely resembling the 

 Echinocorys-Be&s farther south, may possibly belong to a somewhat 

 higher horizon. It may be the equivalent of the limestone which 

 immediately overlies the shales in the base of the cliffs at Thebes. 



The occurrence in the Kom-Ombo region of the Danian Echino- 

 corys-Chalk and of Eocene O^erculina-nummulitiG limestones at 

 river-level, can only be explained on the supposition of faulting of 

 some magnitude. Dr. Blanckenhorn (loc. cit.), without coming to 

 any very definite conclusions, discusses the question as to whether 

 the occurrence is to be explained by the (hypothetical) Eocene- 

 Cretaceous unconformity, or whether it is the result of post-Eocene 

 and pre-Pliocene disturbances. 



At Jebol Silsila, a few miles to the north, the much older 

 Nubian Sandstones form a range of hills rising to a considerably- 

 higher level. In the hill of El Borga, 30 kilometres (18| miles) 

 west of Kom Ombo, the Libyan Limestones overlying the Upper 



1 A list of the Eocene fossils occurring here is given by Dr. Max Blanckenhorn, 

 * Neues zur Geologie & Palaontologie iEgyptens : IV ' Zeitschr. d. Deutseh. 

 Geol. Oesellsch. vol. liii (1901) p. 326. 



2 Dr. Blanckenhorn (op. cit. pp. 327-29) calls especial attention to the part 

 which the disintegration of the soft Lower Eocene and Cretaceous clays has 

 played in the formation of portions of the Nile Valley. 



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