392 Prof. J. W. Dawson — Notes on tlie Geology of Egypt. 



Silsilis ridge. A little below Kom Ombos the sandstone reappears, 

 and continues all the way to Assouan. At one point in tins section 

 two distinct beds are seen, the upper a ferruginous irregular sand- 

 stone and the under grey and laminated. They appear, as seen 

 from the river, to be unconformable, but this may be merely false 

 bedding. At another place the sandstone is seen to be shallow, a 

 mass of dark-coloured crystalline rock appearing below it. At 

 Assouan, however, where it rejDoses on the Laurentian and granitic 

 rocks, it appears in some places to be at least 100 feet in thickness. 



The conformable manner in which the Nubian sandstone under- 

 lies the Cretaceous has induced Zittel and others to consider it as 

 merely a lower member of that formation. Of this, however, there 

 is no distinct evidence, and the only determinable fossil hitherto 

 obtained in the formation — a species of Dadoxylon {D. jEgyptiacum 

 of linger) — has a Palaeozoic rather than Mesozoic aspect. Specimens 

 of this wood have been obtained at Assouan and Kom Ombos, and. 

 Newbold mentions^ the discovery of Coniferous wood at Ipsambul, 

 in Nubia, which must also have been in this formation. On the other 

 hand, Nicolia is also stated to have been found in it, but this I suspect 

 to be an error. In any case the Nubian sandstone is the oldest 

 formation on the Nile next to the old crystalline rocks, to which 

 it clings all along their margin, and from whose waste it is obviously 

 derived. It may not improbably be a Palaeozoic deposit, the upper 

 part of which has been remaine and mixed with the early Cretaceous 

 beds. This would, however, imply a remarkably undisturbed con- 

 dition of the Egyptian area in the later Paleeozoic and earlier 

 Mesozoic periods. There is, however, a similar case in the Triassic 

 red sandstones of Prince Edward Island in the Gulf of St. Lawrence, 

 which rest so conformably and continuously on the upper red sand- 

 stones of the Permo-Carboniferous from which they are derived, that 

 it is about impossible to separate them.^ 



If we aj)peal in this case to the so-called Nubian Sandstones of 

 the Sinaitic peninsula, we find that there Bauerman and others have 

 found Brachiopods of Carboniferous species, as well as Sigillaria and 

 Lepidodendi-on.^ Of these I haA^e seen only the specimen L. Mosai- 

 cum in the collection of the Geological Society, which is in a hard 

 grey sandstone, and has a decidedly Carboniferous aspect. The 

 sandstones of Wady-Nasb, which have afforded these fossils, are 

 connected by a continuous line of outcrop with those of the east 

 side of the Dead Sea, which underlie the Cretaceous of that region, 

 just as the Nubian Sandstone does in Egypt. 



On the other hand, I have examined certain sandstones associated 

 with the lignitiferous zone of the Lebanon, and which have been 

 associated with the Nubian Sandstone ; but these are stratigraphically 

 included in the Cretaceous limestones, and contain Ostrea succinea 

 and other Cretaceous fossils. They hold also fossil coniferous 

 wood, which I have not yet examined microscopically, but it has a 



1 Quart. Journal Geol. Soc. 1848, vol. iv. pp. 349-357. ^ Acadian Geology. 



3 Tate, Quart. Journ. Geol. Soc. 1871, vol. 27, p. 404; Hudleston, Address to 

 Geologists' Assoc, vol. viii. 1883, pp. 1-53. 



