of the Deposits of the Nile Delta, obtained by Boring. 35 



summer of 1885 by Mr. T. E. Cornish, C.M.G., Director of the 

 Alexandria Waterworks, gave a section very similar to that at 

 Zagazig. The object of this boring was to obtain a supply of fresh 

 water for the town of Rosetta, but success not having been attained 

 when a depth of 153 feet 4 inches from the surface had been reached, 

 it was found too costly to carry the work farther. 



Tor details of this interesting boring the Royal Society's Commit- 

 tee is indebted to Sir Colin Scott Moncrieff, R.B., K.C.M.Gr., at that 

 time Under-Secretary of State for the Public Works Department of 

 the Egyptian Government. The boring was carried down by a 

 5-inch tube, the surface being 9 feet 4 inches above mean sea level. 

 Various beds of sand and mud, the latter containing in some places 

 impure lignite, were found down to the depth of 143 feet 8 inches 

 from the surface, but at this latter depth a mass of " coarse sand 

 and pebbles " was found, which was followed down for about 10 feet. 

 No specimens from the boring have reached this country. 



It will thus be seen that in the case of the Zagazig boring we find 

 at the depth of 115 feet 8 inches (89 feet below sea level) a 

 sudden change from the blown sand and alluvial mud of the Nile 

 delta to masses of shingle and sand, and that the same change is 

 found to take place at the Rosetta boring at a depth of 143 feet 

 8 inches (134 feet 4 inches below sea level). That these shingle 

 beds were deposited under totally different conditions to those which 

 prevailed while the delta deposits were laid down, and that they 

 were in fact the product of ordinary fluviatile action, can scarcely 

 be doubted, and the determination of the geological age of the great 

 gravelly deposit which is now shown to underlie the modern delta 

 deposits, and to attain depths which certainly in places exceed 230 

 feet, becomes a problem of the greatest importance and interest. 



That the surface of these old gravelly deposits is a very uneven one 

 is indicated by the difference of depth at which it is found at Rosetta 

 and Zagazig respectively. It is possible, indeed, that this gravelly 

 floor may in places rise through the whole of the Nile deposits, and 

 form the present surface of the country. The late Sir Samuel Baker, 

 in a letter addressed to the Royal Society's Delta Committee on 

 February 20, 1886, called attention to the existence of the so-called 

 " turtle-backs," which he regards as interesting proofs of " the pre- 

 existence of desert, before the Nile deposit had converted the lower 

 level into delta." 



" There are," he says, " several of these turtle-backs, varying from 

 two to twenty acres, which represent the original desert that has, 

 from its superior level, never been subjected to the inundation of 

 the river. These patches of sand appear like islands in the wide 

 expanse of dark alluvium, which exhibits the maximum deposits of 

 the Nile." Several of these turtle-backs may be seen from the rail- 



d 2 



