58 T. Barron — Age of the Petrified Forest, etc., 



serpentine indicates severe crushing (the flaky minerals often 

 resembling antigorite), and contains a few much altered bastite 

 crystals and powdered magnetite, more or less in streaks. It must 

 originally have been a Saxouite, and in its present condition could 

 be matched from several parts of the Alps. The other is labelled 

 " Erzerum-Trebizond. Gorge beyond Pirnakapan. Kop Dagh." ^ 

 It is a dark rock with an external steatitic film, generally greenish- 

 white, but assuming a blue tinge where very thin. The specific 

 gravity is 2'72. Microscopic examination shows it to consist of 

 olivine partially changed into serpentine, bastite, in parts replaced 

 by a mineral with slightly oblique extinction (? tremolite) or a 

 minute fibrous one transverse to and obliterating the cleavages, 

 magnetite in grains and occasionally in a powder (perhaps the 

 latter sometimes hematite). The olivine is less altered than the 

 bastite, for the former in most parts is only in the first stage of 

 change, thin strings of serpentine occupying the cracks. Thus the 

 rock is a partially serpentinized Saxonite not materially affected by 

 pressure. 



IV. — On the Age of the Gebel Ahmar Sands and Sandstone, 

 THE Petrified Forest, and the Associated Lavas between 

 Cairo and Suez, 



By T. Barron, A.B.C.S., F.G.S. 



[Published by permission of the Under-Secretary of State for Public Works, and the 

 Director- General of the Survey Department, Egj'pt.] 



rpHE geological age of these beds has been the subject of much 

 1 speculation by various geologists. In 1845 Orlebar- claimed 

 to have found the Gebel Ahmar Sandstone at No. 3 Station on the 

 Old Post Eoad to Suez, overlying Miocene beds containing Scutella 

 Zitteli. 0. Fraas^ in 1867 imagined he could trace a gradual 

 passage between the Upper Moqattam and these beds, and con- 

 cluded, therefore, that they were of marine origin and Lower 

 Oligocene age, as they had undergone the same general earth- 

 movements as the Eocene beds. 



Dr. Schweinfurth,* discussing the age and origin of these beds, 

 says that there are two reasons for concluding that they are not 

 marine : (1) they occur at different levels in various localities, and 

 (2) they rest on a very uneven surface which does not differ 

 much from the present-day relief. He, in fact, considers that the 

 present-day relief of the surface had already been inaugurated 

 before these beds were laid down. He also calls attention to 

 the resemblance existing between the Pliocene sands in the Nile 

 Valley and these beds, and finally groups them together in his map 

 as (?) Pliocene. 



^ Lynch: "Armenia," vol. ii, p. 229. 



- " Some observations on the Geology of the District between Cako and Suez " : 

 Journ. Eoy. Asiatic Soc, 1845. 



* " Aus dem Orient," 1867, pp. 157-8. 



* " Geol. Schichtengliederung d. Mokattam": Zeitschr. d. Deutsch. Geol. Gesells., 

 1883, p. 719etseq, 



