600 Dr. W. F. Hume — Metrography of Egypt. 



IV. — Notes on the Pktrogeapht of Egtpt.^ 



By "W. F. HvME, D.Sc, A.R.S.M., F.G.S., Superintendent, Geological 

 Survey of Egypt. 



(WITH A PAGE MAP.) 



PRIOR to the foundation of the Geological Survey of Egypt in 1896, 

 the general relations of the sedimentary strata had already been 

 established on a firm basis by the labours of numerous observers, but 

 the characters and affinities of the igneous and metamorphic rocks had 

 been but little investigated. Such studies as had been made were 

 more or less isolated in character, those that had been carried out 

 including a description of rock- specimens from the First and Second 

 Cataracts by Newbold,* Delesse,^ Dawson,* Bonney,* and Miss Raisin,® 

 of the Abu Zabel basalts by Arzruni, of some Eastern Desert rocks by 

 Liebisch (Zeitschr. d. Deutsch. Geol. Gesellschaft, 1877, xxix, p. 712), 

 and, in addition, the principal ornamental rock of Egypt, the Imperial 

 Porphyry, had received special attention (see references in Barron & 

 Hume, " Eastern Desert of Egypt," p. 236, etc.),' but a general 

 picture of the petrographical history of Egypt as a whole has not yet 

 been delineated. Pending a more detailed description of the Egyptian 

 igneous and metamorphic rocks, the following epitome of the results 

 already obtained may be of interest, the region under consideration 

 embracing Egypt and the Sudan, the peninsula of Sinai, and the 

 countries immediately adjacent. 



The subject may be most conveniently considered under the 

 following six divisions : — 



I. — Gneisses : {a) Cataract gneisses, (i) Arabian Desert gneisses. 

 II. — (c) Pre-Carboniferous plutonic rocks, id') red granite, 

 (e) igneous dykes. 

 III. — Pre-Carboniferous volcanic and sedimentary series. 

 IV. — Ancient metamorphics of schistose character. 

 V. — Carboniferous and post- Carboniferous volcanic activity. 

 VI. — Early Tertiary volcanic occurrences. 



I. — Gneisses. 



(«) There is little doubt that the ancient continental core of this 

 vast area is represented by the Cataract and Sudan gneisses and 

 schists, which often display banding of marked character, both the 

 more closely foliated schists and highly crystalline gneisses being 



1 A brief abstract of this paper appeared in the Geological Magazine for 

 October, p. 465. Read at British Association, September 4, 1908. Given by 

 permission of Director-General, Survey Department. 



« " On the Geology of Egypt " : Q.J.G.S., 1848, vol. iv, pp. 324-49. 



3 "On the Rose- Coloured Syenite of Egypt " : Q.J.G.S., 1851, vol. vii, pp. 9-13. 



4 " Geology of Egj^jt " : Geol. Mag., 1884, pp. 289-92, 385-92, 439-42. 



' " Note on the Microscopic Structure of some Rocks from the neighbourhood of 

 Aswan " : Geol. Mag., 1886, pp. 103-7. 



6 Geol. Mag., 1893, pp. 436-40, and Q.J.G.S., 1897, vol. liii, pp. 364-73 

 (on rocks collected by Captain Lyons). 



' There are also some notes on the rocks from the Sinai Peninsula by Professor 

 Bonney in Palmer's "Desert of the Exodus" (1871, p. 556), and by Mr. Rudler 

 in Appendix B of Professor Hull's Memoir on the Geology, etc., of Arabia Petra3a. 



