of the Deposits of the Nile Delta, obtained by Boring. 39 



oolitic grains (silicified) were detected. This rock may have come 

 from a Cretaceous deposit, and not from the Eocene like the others. 



Of the general sources from which these pebbles were derived 

 Dr. von Zittel writes as follows : — 



" On the whole it appears to me conceivable that these gravels 

 under the delta originated at a time when the Nile had already 

 formed its present valley, but not to so great a depth as at present. 

 The majority of the rolled rock-fragments would seem not to have 

 been derived from points extremely distant from those in which they 

 are at present found." 



In considering the nature and sources of the pebbles found, in the 

 boring at Zagazig, it may be well to point out that the spot where 

 the boring was carried out is directly opposite to the Great Wady 

 (W. Tumilat), which opens on the delta from the east, and that 

 much of the materials composing the gravels may have been brought 

 down by this tributary rather than by the main stream of the Nile 

 itself. Hence we may not have in this particular section so good an 

 average sample -of the contents of the Sub-delta formation as would 

 be obtained at other localities. 



There can scarcely be the smallest doubt that in this Sub-delta 

 formation we have a series of deposits, which were formed under 

 totally different conditions from those which prevail in North 

 Eastern Africa at the present time. The land must have been at an 

 elevation at least from 100 to 300 feet higher than at present, and 

 the Lower Nile, instead of forming an alluvial fiat, as at present, 

 must have deposited coarse sands and gravels. It is upon the very 

 uneven surface of this Sub-delta deposit that the alluvial mud and 

 sands of the deHa have been deposited, as the surface gradually sub- 

 sided below the level of the Mediterranean. 



The interesting problem of the geological age of this Sab- delta 

 deposit remains to be solved, but it may be hoped that the explora- 

 tions now being carried on by the Geological Survey of Egypt, under 

 Captain H. G. Lyons, R.E., E.G.S., may furnish new and important 

 evidence bearing on this important question. 



It is to be regretted that the borings carried out by the Royal 

 Society have not set at rest the doubts which have long existed as to 

 the depth at which the solid rock-floor lies below the surface of the 

 delta. But while this has not yet been accomplished, it is satis- 

 factory to have been able to show that the supposed insignificant 

 thickness of the alluvial deposits is altogether a mistake, while the 

 existence of an underlying formation, laid down under conditions 

 totally different to those which prevail at present, has been demon- 

 strated. 



Communications have lately passed between the English War 

 Department, the Egyptian Public Works Department, and the Royal 



