102 Sir J. W. Daicson — Rocks of Assouan on the Nile. 



traversed by great dykes of diorite, and the mass or dyke of granite 

 which, has been the most extensively quarried is situated to the north 

 along the course of the same ridge. Some of the crumbling schists 

 seen in the valley behind the town may have been calcareous, and 

 may be associated with limestone now concealed, but no limestone 

 was observed, though the character of the beds in comparison with 

 those I have elsewhere seen might lead to the expectation of its 

 occurrence in the vicinity. 



The Nubian sandstone, where it rests on these rocks, has, in its 

 base, layers of conglomerate and of a calcareo-argillaceous indurated 

 marl, but holds no fossils. It may be of Cretaceous age, but I should 

 infer, from the character of the fossil wood (Araucarioxylon 

 ^gyptiacum) l found in it elsewhere, and described by Schenk 

 in Zittel's work on the Geology of the Nubian desert, that its lower 

 beds at least may be Permian or Carboniferous. 



The lithological aspect of the beds seen in the cutting at Assouan 

 is that of the Middle or Grenville series of the Laurentian in 

 Canada; indeed I find on comparison that the greater part of the 

 rocks are not distinguishable in hand specimens from those occurring 

 in this series on the Ottawa Biver. 



In the Island of Biggeh, above the cataract, and on the higher 

 parts of the mainland in its vicinity, there appears another formation 

 (Series C in Note), very different in its mineral character, which, 

 though older than the Nubian sandstone, I believe to rest uncon- 

 formably on the older Assouan Series. In Biggeh the latter is seen 

 in the lower part of the island in a vertical attitude and with strike 

 N. 10° W. Strikes ranging from about N. 10° W. to N. 10° E. 

 appear to prevail in this series, in the vicinity of the cataract, though 

 in one place east of Assouan it was observed to be N. 70° E. Eising 

 above the lower series, and apparently resting upon it unconformably, 

 is a second series of beds nearly horizontal, and about 100 feet in 

 thickness. They are composed as follows in ascending order : — 



(1) Hard dark-coloured quartzose porphyry, with crystals of red 

 orthoclase. 



(2) Fine-grained granulite or granite, possibly a remanie rock. 



(3) Black fine-grained laminated and in some places shaly rocks, 

 referred by Professor Bonney to quartziferous kersantite. 



(4) Granulite, like No. 2. 



(5) Dark-coloured porphyry, with dark crystalline paste, and large 

 crystals of opaque brick-red orthoclase. 



The last is a very thick bed, and dividing along straight joints into 

 huge cubical blocks, gives a castellated appearance to the hill and 

 cliffs composed of this formation. 



As seen from a distance, these rocks of the Second or Upper 

 Assouan series appeared to be intrusive masses ; but on nearer 

 examination, they showed horizontal bedding, and at the base of the 

 cliffs and in their ravines were seen to rest on the older series. 



Assuming on the evidence of mineral character the Lower Assouan 

 series to be Laurentian, and of Middle Laurentian age, the next 



1 See W. Carruthers in Geol. Mag. 1870, Yol. VII. p. 306, PI. XIV. 



