536 CAPT. H. G. LYONS ON THE STRATIGRAPHY AND [Nov. 1 894, 



consist of a series of limestones and calcareous sandstones, and marls 

 and clays of marine origin, overlain by freshwater beds, also of 

 Miocene age. These last consist of limestones, and beds of quartzose 

 sandstones having the grains bound together with a siliceous cement 

 indistinguishable in hand-specimens from the Jebel Ahmar Sand- 

 stone. The uppermost freshwater beds are sandy, with layers of 

 fine-grained chalcedonic quartz. 



The rocks of the Wadi Natrun south of the Natron Lakes are, I 

 think, of Miocene age, and possibly of the freshwater series, though 

 I have not at present any definite evidence to produce on this 

 point. Lithologically they appear to agree closely with the fresh- 

 water beds of Siwa as described by Dr. Zittel, but further exami- 

 nation of them is necessary. 



Marine Miocene beds occur also between Cairo and Suez, at Jebel 

 Geneffe and also between Jebel Atakka and Jebel Gallala in 

 "Wadi Baida. 



Overlying these Miocene beds of the Wadi Natrun is a sandstone, 

 usually grey to yellow in colour (though here and there patches 

 occur of a dark red to almost a black colour, due to oxides of iron 

 and manganese), moderately fine-grained, of average hardness, and 

 intensely tough, a toughness due to the siliceous cement binding the 

 grains. This is the form in which it occurs at Jebel Ahmar, near 

 Cairo, whence it has often been described. 1 



In some parts it contains fossil trees (principally Araucarioxylon, 

 Palmoxylon, Nicolia, etc. 2 ), and the principal localities are the 

 ' Petrified Forests' 12 miles E. of Cairo, Xum el Khashab (12 miles 

 W. of the Giza pyramids), and the desert west of the Fayuni and 

 south of the Wadi Natrun, as far as lat. 29° N. 



It often happens that the toughest and most durable sandstone 

 occurs near large deposits of the fossil trees. Thus Jebel Ahmar is 

 on the east and Jebel Raibun on the west of the petrified forest 

 near Cairo ; while at Kum el Khashab, near Giza, the same sandstone 

 occurs, and 20 miles W.S.W. of Der Baramus, in the Natron Lakes, 

 I came upon an exposure of this tough, almost black sandstone, 

 where the desert was covered with numerous fossil trees. 



Over all this area we meet with fossil wood in pieces of all sizes, 

 from small fragments to masses 1 or 2 feet in length, and up to 

 trunks of 30, 40, and even 50 feet long, and 2 to 3 feet in 

 diameter, all completely silicified. These are scattered broadcast 

 over the surface of the sandstone area, sometimes grouped rather 

 closely for several miles. They are all lying horizontally in every 

 direction, half embedded in the sand, the only cases of pieces found 

 in an upright position being where they had been set up as road- 

 marks by the Arabs. As the southern limit of the sandstone was 

 approached trunks grew scarce, and finally only small fragments 

 occurred for the last 20 miles. 



1 Newbold, Quart. Journ. Geol. Soc. vol. iii. (1848) p. 335 ; Dawson, Geol. 

 Mag. 1884, p. 385 ; Schweinfurtb, Zeitschr. deutsch. geol. Gesellsch. vol. xxxv. 

 (1883) p. 718. 



2 A. Schenck, ' Palseontographica,' vol. xxx. (1883) pt. ii. 



