'Rocks in the Nile Valley^ in Nubia. 143 



very type of the rock on which the oldest strata of the earth were 

 founded, is said to have burst forth during the later tertiary period. 

 We learn from Russegger, that the low land which lies between the 

 Mediterranean and the range of hills that extends from Cairo to the 

 Red Sea at Suez, and of which hills a nummulite limestone consti- 

 tutes a great part, is composed of a sandstone which he calls a 

 " Meeresdiluvium," a marine diluvial formation, and considers to be 

 of an age younger than that of the sub-appennines.* This sandstone 

 he found associated with the granite above Assuan, and covering the 

 cretaceous sandstone far into Nubia. It appears, therefore, that, in 

 the later ages of the tei'tiary period, this north-eastern part of Africa 

 must have been submerged, and that very energetic plutonic action 

 was going forward in the then bed of the sea. The remarkable fact 

 of the granite bursting through this modern sandstone is thus de- 

 scribed by Russegger : — 



'* We arrived at a plateau of the Arabian Chain south-east of As- 

 suan. It is about 200 feet above the bed of the Nile, and consists of the 

 lower and upper sandstone, which are penetrated by innumerable granite 

 cones from 20 to 100 feet in height, arranged over the plateau m parallel 

 lines, very much resembling volcanic cones rising from a great cleft. The 

 sandstone is totally altered in texture near the granite, and has all the 

 appearance as if it had been exposed to a great heat. ' I cannot refrain,' 

 he says, ' from supposing that the granite must have burst, like a volcanic 

 product, through long wide rents in the sandstone, and that, ia this way, 

 the conical hiUs were formed.' "f 



An eruption of a true granite during the period of the sub-appen- 

 nine formations, one possessing the same mineral structure as that 

 we know to have been erupted during the period of the palaeozoic 

 rocks, would be a fact of so extraordinary a kind, that its age would 

 require to be established on the clearest evidence, and especially by 

 that of organic remains in the sandstone. 



Having thus ventured — I trust without any want of the respect due 

 to so eminent a person — to reject the hypothesis proposed by Profes- 

 sor Lepsius for the high levels of the Nile at Semne, indicated by 

 the sculptured marks he discovered, it may perhaps be expected that 

 I should offer another more probable explanation. If in some nar- 

 row gorge of the river below Semne, a place had been described by 

 any traveller, where, from the nature of the banks, a great landslip, 

 or even an artificial dam, could have raised the bed to an adequate 

 height ; that is, proportionate to the fall of the river, as it was more 

 distant from Semne, a bar that, in the course of a few centuries, 

 might have been gradually washed away, I might have ventured to 

 suggest such a solution of the problem. But without any informa- 

 tion of the existence of such a contraction of the river's channel, or 



Reisen, Hd. I., s. 273. t Id., Bd. II., I. Thl. s. 



