52 nubian sandstone and crystalline rocks [feb. 1909, 



Discussion. 



The President remarked that the Author's observations, thougb 

 of great interest, scarcely sustained his contention. Disturbances 

 in dip might be due to various kinds. of movement. No conclusion 

 could be drawn from the absence of granite-pebbles in the over- 

 lying sediments ; for, in isolated exposures of obvious unconfor- 

 mities, pebbles derived from the underlying rock were not un- 

 commonly absent from the unconformable covering. The evidence 

 of contact-metamorphism was very indefinite. 



Prof. Hull, while recognizing the zeal of the Author and the 

 difficulties of observation in the Egyptian desert, was unable to 

 accept his conclusions regarding the relations of the Nubian Sand- 

 stone to the granitic and crystalline rocks, either of Egypt or of 

 Sinai. The Author had not adduced a single instance of intrusion 

 of the granite into the sandstone, or of the former overlying the 

 latter at the place of contact. Erom his own observations at 

 Aswan, and also in Arabia Petraea and the Sinaitic Peninsula, it 

 was quite clear to him, as it had been to the observers whom the 

 Author had quoted — that the crystalline rocks were immensely 

 older than the sandstone-formations of those regions ; and he 

 believed that the former had been rightly referred by Fraas in 

 'Aus dem Orient' to the Archaean Era. The Author did not 

 seem to have been aware that, in the Sinaitic Peninsula, there were 

 two sandstone-formations, separated one from the other by the 

 Carboniferous Limestone, discovered some years ago by Mr. H. 

 Bauerman. This limestone-plateau at Wady Nash had been visited 

 by the speaker, during his passage through the country with the 

 members of the Expedition sent out in 1883-84 by the Palestine 

 Exploration Committee, and a collection of fossils was brought 

 home, the organisms being identified as those of the Carboniferous 

 Limestone. This formation rests upon a lower sandstone-formation, 

 reddish or variegated, and often conglomeratic, laid down over an 

 uneven floor of the crystalline rocks ; and, being altogether older 

 than the Nubian Sandstone, it had been named by the speaker 

 ' The Desert Sandstone.' He begged to refer the Author to the 

 Memoir drawn up for the Palestine Exploration Fund on 'The 

 Physical Geology & Geography of Arabia Petraea ' (1886), which he 

 did not appear to have seen, although it had been quoted in the 

 reports of the Geological Survey of Sinai under Capt. Lyons. 

 Throughout the whole of that region there was no case of these old 

 crystalline rocks, or of the dykes (which were numerous), invading 

 either of the sandstone-formations. 



Mr. Hudleston said that he felt a certain amount of hesitation 

 in intervening in the discussion, as he had never visited the 

 district described. It was perfectly clear, however, that the Author 

 was at variance with the whole literature of the subject, and he 

 (the speaker) was very much inclined to be of the same opinion as 

 Prof. Hull, in regard to the Author's mistaken view of the relation- 

 ship of the crystalline rocks to the Nubian Sandstone. There was 



