440 Sir Wm. Bauson — Notes on the Geology of Egypt. 



Eastward of the cutting, the ground becomes flat, and does not 

 afford a continuous section ; but the decayed edges of micaceous and 

 hornblendic schists, and thin-bedded gneisses appear at intervals of 

 about 800 yards, after which they are overlain by the base of the 

 Nubian sandstone, which further east rises into the table-land of the 

 Arabian desert.^ The base of the sandstone at this place shows a 

 thin bed of conglomerate, and upon this some soft calcareous layers, 

 above which is the ordinary grey sandstone. 



The above section represents at least two thousand feet in thick- 

 ness of crystalline schists and gneiss, with granite veins. To the 

 latter category belongs the huge dyke of granite at the north end of 

 the ridge, in which are the principal Egyptian quarries, though 

 there are other ancient quarries in granite, diorite, and sandstone in 

 several places in this vicinity. One of the diorites has a porj)hyritio 

 character, caused by crystalline patches of white felspar, and this 

 stone appears as a material of statues and other objects in all parts 

 of Egypt. Two sphinxes from Pithom, now in the square of Ismalia, 

 are of this material. There are also dykes of a black basaltic rock. 

 No crystalline limestones were observed, but from the manner in 

 which the surfaces of the gneiss and schist are disintegrated, it 

 may be inferred that the outcrop of limestones, if present, would 

 be deeply eroded and concealed. 



Many of the granite dykes extend in the plane of the stratifica- 

 tion, and for this reason it is not always easy, without careful obser- 

 vation, to distinguish them from the beds of gneiss. They are, 

 however, generally coarser, and not laminated, and can be observed 

 to send off branches into the adjoining beds. The mica present in 

 schists seems to be in all cases biotite rather than muscovite. 



At the Island of Biggeh, above the Cataract, and near to Philse, 

 there appears to be a second crystalline formation resting in a hori- 

 zontal position on the older gneiss and schists, and itself overlaid by 

 the Nubian sandstone. The precise arrangement of these rocks 

 could not be seen so clearly as was desirable, owing to the debris 

 which covered the sides of the cliffs ; but on the Island of Biggeh 

 their order appeared to be as follows, in descending series : — 



1. Coarse dark-coloured porphyritic rock with large crystals of deep red felspar, 



darker ia colour and more opaque than that of the lower series. This rock 

 breaks into cuboidal masses, giving the cliffs composed of it a remarkable 

 castellated appearance. 



2. Fine reddish gneissose rock. 



3. Black fine-grained coarsely laminated beds. 



4. Coarse porphyritic rock, resembling No. 1. 



Below this are the schists of the lower series, in a position nearly vertical. 



The whole thickness of this upper series appeared to be about a 

 hundred feet. On the mainland east of Biggeh it forms a high ridge 

 stretching to the eastward. Whatever the origin of these rocks, they 

 appear to overlie unconformably the lower series, and they did not 

 appear to be penetrated by the great granite veins. They are, how- 

 ever, traversed by veins of red felsite and of a black igneous rock, 

 having the appearance of basalt. 



^ In approaching the sandstone the strike of the schists changes to about N. 70° E. 



