Dr. John Ball— The Gulf of Suez. 9 



northern part of Egypt, as is most likely, the Nile must have eroded 

 its channel 60 metres or more below its present level in order to reach 

 the sea ; we have thus a simple explanation why the bed-rock channel 

 of the Nile in Lower Egypt is so deep. 



A great part of the erosion of the Nile Valley, and a still greater 

 part of that of the Gulf of Suez, must have been accomplished 

 between the Miocene and Pliocene epochs, when the land was at its 

 maximum elevation. It is, indeed, likely that there has been 

 practically no erosion of the bed-rock main channel of the Nile in the 

 neighbourhood of Cairo, nor of the central line of the Gulf of Suez, 

 since Pliocene times; and this not because of any cessation of the 

 action of erosive forces in the district generally, but merely because 

 these forces have been unable to exert themselves in these particular 

 places ; for the bed-rock channel of the Nile near Cairo has never 

 since that time been above sea-level, and the Gulf of Suez has been 

 continually an arm of the sea. Erosion was, however, going on with 

 great vigour throughout the Pliocene and Pleistocene ages in all the 

 tracts which remained unsubmerged. In the case of the Nile Valley 

 the river continually cut backwards higher up its course, and the 

 lateral drainages to it were actively eroding their channels, while 

 there were doubtless migrations of the stream from side to side, 

 tending to the continual broadening of its valley, in which river 

 erosion was aided by weathering and landslips at the faces of the 

 confining scarps. In the case of the Gulf of Suez the lateral 

 drainages only have been active in erosion since the submergence of 

 the trunk channel, but the vast extent to which this action has gone 

 on is attested by the size of the Wadi Araba and the breadth of the 

 sloping plains, covered with sand and gravel, which stretch in most 

 places between the hills and the shores of the gulf. 



In Pliocene and early Pleistocene times a subsidence of the land 

 took place, submerging the lower part of the Nile Valley and the 

 whole Isthmus and Gulf of Suez. The Pliocene sea entered the Nile 

 Valley, deposited the Clypeaster sands near the pyramids, and gave 

 rise to the Pholas borings in the face of the Mokattam Hills. The 

 northern parts of the Nile Valley being submerged, the river would 

 have its velocity checked by entering the sea at an earlier point of its 

 course than formerly, and would thus be forced to deposit the sands 

 and gravels which now overlie the bed-rock in the lower reaches of 

 its channel. The sinking of the land to a depth of over 60 metres, 

 which is necessary to account for the Clypeaster sands, the Pholas 

 borings, and the old shore-line near Suez, must have submerged the 

 Isthmus of Suez, and brought about that connexion between the 

 Mediterranean and Red Seas which is evidenced by the mingling of 

 the two faunas. The same sinking accounts for the raised beaches 

 found along the shores of the gulf ; to explain the higher beach, 

 158 metres above present sea-level, we have only to assume, what is 

 indeed most likely, that the downward movement varied in amplitude 

 in different parts, and reached its maximum amount in the district 

 where this higher beach is found. 



In the later Pleistocene period subsidence ceased, and elevation of 

 the land set in. The Isthmus of Suez again became dry, and the two 



