﻿12 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 6, 



belong to the lower part of the cretaceous formation, or the Quader- 

 sand stein : near Fatireh it is covered with a white earthy chalk, 

 having a somewhat conchoidal fracture, that reposes on it in con- 

 formable and horizontal strata. 



The quarries in which the ancients worked the syenite have been 

 observed by all travellers who have visited Egypt ; they are princi- 

 pally south of Syene, and between Syene and the island of Philae. 

 The detached blocks of the syenite, near the cataract, are sometimes 

 of a spheroidal form, and are separable into concentric layers ; ac- 

 cording to Lieut. Newbold, however, the dry and hot climate of 

 Egypt preserves the granite rocks much more from decomposition 

 than the climate of India. 



M. Russegger remarks, that near the cataract, the blocks found in 

 the river, or at a small distance from it, are covered with a very thin 

 and brilliant substance resembling black pitch. This coating, so 

 strongly united with the rock as to be quite inseparable, is considered 

 by M. Russegger to be oxidulated iron*. 



Messrs. Russegger and Lefevre were struck by the fact, to which 

 they frequently afterwards alluded, that the syenite of Egypt is tra- 

 versed by a multitude of large veins of diorite, which is particularly 

 the case along the cataract, near Philse, in the neighbourhood of 

 Syene, &c.; these diorite veins are however well known, for they also 

 were worked by the Egyptians f. 



This association of syenite and diorite is not accidental ; and I have 

 made similar observations on all the syenites that I have studied in 

 situ. Indeed I could almost always find that they were associated 

 with diorites. Thus, at the Vosges especially, the syenite of the 

 Ballons is accompanied by diorites, which are sometimes at the bottom, 

 sometimes on the sides of the Ballons of Alsace and Conte, forming 

 either veins, fairly separated from the syenite and enclosed by it, or 

 dykes uniting with and insensibly passing into the syenite. 



It would hence appear, that the development of amphibole in 

 the syenite is in intimate relation with the contents of the veins of 

 diorite enclosed therein, and subsequently metamorphosed into am- 

 phibole. 



It is, however, necessary to add, that if the syenite be generally 

 associated with diorite, the contrary is not always the case ; also, if 

 a diorite form a vein in a granite, it must not thence be concluded 

 that crystals of amphibole had been therein developed by that cir- 

 cumstance alone, and that such granite had been metamorphosed into 

 syenite : at the Vosges, for instance, the granite is sometimes tra- 

 versed by veins of diorites and yet is not amphibolous. 



The Egyptians made great use of syenite ; subsequently it was 

 worked by the Greeks, and after that by the Romans. The syenite 

 of Egypt is still sometimes employed instead of marble, and its price 

 may be approximately estimated at 200 francs per square metre po- 

 lished ; it is brought as ballast by vessels trading with Alexandria, and 

 is designated in commerce by the name of the Eastern Red Granite%. 



* Russegger, vol. ii. p. 321. f Ibid. vol. ii. p. 320, 322, 326, &c. 



X Brard, Mineralogie appliquee aux Arts, t. ii. p. 241. 



