Sir Wm. Dawson — Notes on the Geology of Egypt. 439 



II. — Notes on the Geology of Egypt.' 



By Sir William Dawson, K C.M.G., LL.D., F.E.S., F.G.S., etc. 



Principal of McGill College, Montreal. 



IV. — The Crystalline Bocks of Upper Egypt. 



A SUDDEN and great change takes place in the geology of the 

 Nile valley in approaching the First Cataract, where we pass 

 from the unaltered and nearly flat Nubian sandstones to rocks highly 

 crystalline, greatly disturbed, and penetrated with multitudes of 

 igneous veins. 



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d d d d d 



Relations of Crystalline JRocks and Nubian Sandstone at First Cataract. 



(a) Older Crystalline Series (Laurentian). (d) Dykes of Granite and Diorite. 



(b) Second Crystalline Series (Arvonian). (e) Dykes of Felsite and Basalt. 



(c) Nubian Sandstone. 



The gneisses and schists associated with granite and diorite at 

 Assouan and its vicinity, though they have attracted the attention of 

 the most unscientific travellers, have apparently as yet been little 

 studied in detail. They have, however, been described by Lieut. 

 Newbold in the Journal of the Geological Society of London, vol. iii., 

 and in the same journal, vol. xxiii. Mr. Hawkshaw has given a good 

 map of their distribution, and has noticed most of the kinds of rock, 

 though without inquiry as to their precise age or general mode of 

 arrangement. 



The town of Assouan is situated at the northern end of a ridge of 

 crystalline rock, which runs about south ten degrees west, along the 

 side of the river towards the Cataract. South of the town a cutting 

 has been made across this ridge for railway purposes, and affords a 

 good opportunit}'^ for studying the structure of the formation. The 

 following section is exposed in this cutting, beginning at the western 

 end, the beds being nearly vertical, and with strike E. 10° N. : — 

 Micaceous and hornblendic schists, with many red granite veins, one 



of them holding nests of broad-leaved magnesian mica 66 paces. 



Dyke of coarse-grained hornblendic granite, with reddish orthoclase 6 ,, 



Schists, as before, with large granite veins 63 ,, 



Gniess, with granite veins 7 , , 



Schist, with much black mica 23 ,, 



Coarse orthoclase gneiss with beds of schist 20 ,, 



Micaceous and hornblendic schists 7 , , 



Gneiss and schist 3 ,, 



Schists and gneiss 7 , , 



Orthoclase gneiss 7 ,, 



Hornblendic and micaceous schist, with veins of coarse granite .... 41 „ 



The same, with veins of red felspar 37 , , 



Micaceous and hornblendic schists, much weathered at the surface . . 34 ,, 



Total 311 paces. 



1 See also former articles, pp. 289-292, 385-393. 



