Vol. 52.] PROP. E. HULL ON THE GEOLOGY OF THE NILE VALLEY. 311 



4. Relation of the Nubian Sandstone to the Granite and 

 Schist of Assuan. 



The only other point bearing on the geology of the Nile Valley to 

 which I shall refer is the relation of the Nubian Sandstone to the 

 older rocks of Assuan and the Pirst Cataract. I should not have 

 thought it necessary to do so, had not some observers supposed 

 that the granite is intrusive into the newer formation. From an 

 examination of the junction at several places, I have satisfied myself 

 that there is no good warranty for this view. Undoubtedly the 

 original surface of the older rocks was very uneven, consisting of 

 ridges and furrows against, and upon, which the Sandstone Series 

 was deposited. But the latter is not in the least ' baked ' or 

 * altered ' along the surface of contact, while the local basement- 

 beds are often conglomeratic, pebbles of quartz, probably derived 

 from the granite itself, being abundant. The junction is remarkably 

 well shown above the ancient quarries, along the pathway leading 

 to the barracks which overlook the Nile Valley, and the accom- 

 panying sketch was taken on the spot. 



Fig. 2. — Sketch of junction of granite and Nubian Sandstone near 

 the Barracks, south of Assuan. 



1 = Coarse brown grit. 



2= Grey and purple sandy shale 



(10 feet). 

 3= White freestone, coarse to fine, 



with quartz-pebbles. 



G= Granite, weathering into rounded 

 masses. 



B = Basalt-dyke, 8-10 feet wide. 



The general structure of the locality is illustrated in the above 

 section, taken from the banks of the river opposite the Island of 

 Sehel, about 3 miles south of Assuan. 



5. Age of the Nubian Sandstone. 



I shall not enter here on the question whether the whole of the 

 Nubian Sandstone of the Nile Valley is of Cretaceous age, or 

 whether it is partly Carboniferous. It is a problem which can 

 be solved only by a careful survey of the whole region, which, as 

 announced, is to be immediately undertaken by the Egyptian 

 Government, under the direction of Capt. Lyons. I will only 

 observe that some portions of the formation which I was able to 

 examine in the Nile Valley are very unlike in mineral composition 



