Geology and Mineralogy. 75 



stone. The absence of limestone and pebbles was striking, the 

 softer rocks apparently having been entirely worn away. In the 

 shingle beds pebbles were also found of igneous rocks, which, it 

 is suggested, may have been derived from the side valleys of the 

 Arabian Desert. A number of the pebbles of flint and flinty 

 limestone contained foraminifera and, apparently, sponge-spicules. 

 These fossils are regarded by Prof. Rupert Jones as proving that 

 the fragments containing them were derived from the Eocene 

 (Nummulitic) limestones of Egypt, thus fully confirming the con- 

 clusions of Dr. von Zittel. 



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." 



Prof. Judd adds : " 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 sam- 

 ple 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 flat, as at pre- 

 sent, 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 delta have been deposited, as the surface 

 gradually subsided below the level of the Mediterranean. The 

 interesting problem of the geological age of this Sub-delta 

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

 explorations now being carried on by the Geological Survey of 

 Egypt, under Captain H. G. Lyons, R.E., F.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 

 satisfactory to have been able to show that the supposed insigni- 

 ficant 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 demonstrated." 



