506 Dr. W. F. Hume — Petrography of Egypt. 



Closely associated with these evidences of intense volcanic activity 

 are the metamorphosed sedimentary strata which, once grits and 

 conglomerates, are now changed to slates and crushed conglomeratic 

 heds. Isolated occurrences of these rocks, and especially the con- 

 glomerates, had heen recorded, for instance, by Prof essor Hull in Sinai, 

 and by Captain Lyons on the road between Korosko and Abu Hamed, 

 while the Breccia Verde Antico of Hammamat was well known to all 

 archaeological students. These rocks are now known to be developed 

 throughout the desert from East Sinai to the confines of the Sudan. 

 Occurring to the north in isolated areas, they play a most important 

 part in the Eastern Desert of Egypt in lat. 26° N. 



This ancient series often presents the most interesting metamorphism 

 where it comes into contact with or overlies the granitic rock. 

 M. Couyat, who had the advantage of studying under M. Lacroix, has 

 pointed out to me that the remarkable basic-looking fringes surrounding 

 some of the granitic masses agree in all particulars with the ' roches 

 eorneennes,' and thus represent contact alterations of the sedimentary 

 rocks by the granite with which they are in immediate contact. In 

 East Sinai, in a district north-west of Nebk, a palm-grove on the Gulf 

 of Aqaba, the contact-phenomena are very striking. Veins from the 

 granitic intrusive mass have in some parts penetrated between the 

 laminfe of the sedimentary slates, giving rise to a rock having the 

 appearance of a mica-gneiss, the well-known lit par lit structure. 

 Elsewhere the sediments, probably in part volcanic in origin, have 

 been altered to hornblende -schists ' near the point of contact, and 

 gradual stages can be traced from this marked alteration at the 

 boundary to garnetiferous mica-schists and spotted slates in the 

 central portions of the areas. The sedimentary strata show every 

 variation from fine-grained slates to conglomerates made up of the 

 most varied materials, among which granites and porphyries are 

 conspicuous. In places they contain quartz -pebbles which have been 

 fractured and recemented, and their detailed study will undoubtedly 

 throw much light on their origin and derivation. The absence of any 

 fossil evidence renders the determination of their age a matter of 

 comparison only. It may be stated broadly that they are pre- 

 Carboniferous and post- Archaean, and appear to have close lithological 

 resemblances to the Pebidian beds of Wales. 



IV. — Ancient Metamoephics of Schistose Character. 



In addition to the coarse gneisses of the Cataracts and the 

 metamorphosed ancient sedimentaries, there is a series of rocks which 

 may in part be connected with the first-named, and in part represent 

 the remnants of an older period of sedimentation and vulcanicity. 

 This includes the highly-foliated, dark, emerald-bearing mica-schists of 

 Sikait, with which are associated beds rich in talc and tourmaline. 

 These rocks immediately overlie a highly banded gneiss, and in Sikait 



' The writer has stated the opinion to which he was led by the field relations in 

 dogmatic form, but fully recognizes that the conditions are exceptional. The 

 ordinary explanations of the origin of these schists failed to satisfy the conditions 

 observed. 



