386 Prof. J. W. Dawson — Wotes on the Geologi/ of Egypt. 



silicified. I consider the appearance decisive as to this point.^ On 

 the other hand, I could see no evidence that the trees are actually 

 in the place of their growth. There seemed to be no " dirt-bed " 

 or fossil soil. It seems probable, therefore, that the sand which 

 was ultimately derived from the crystalline rocks of the interior, 

 and perhaps proximately from the waste of the Nubian sandstone 

 and the sandy Upper Eocene beds, was deposited in the vicinity 

 of a wooded coast, or at the mouth of a river flowing through a 

 wooded country, and that the trees are drift trunks imbedded in it. 

 Their silicification is no doubt due to the presence of the siliceous 

 springs to which the sand itself owes its induration. These springs, 

 and perhaps also to some extent the deposition of the sandstone 

 itself and its contained trees, maj' have been indirectly connected 

 with the Tertiary volcanic phenomena which Schweinfurth has 

 discovered - elsewhere in Lower Egypt. The thickness of these 

 sandstones near Cairo must be about 100 feet. 



The fossil wood of Jebel Ahmar and the petrified forests have been 

 examined and partially described by various authors.^ It includes 

 several species of Nicolia, also Conifers and a Palm. Its affinities 

 have been discussed by Botanists, and it may be regarded as an 

 African Flora allied to that of the Soudan, and not improbably of 

 Miocene age.* 



It may be woi'thy of remark that while this hard sandstone is 

 now used only for millstones and for macadamizing the roads, it 

 furnished to the ancient Egyptians the material of some of their 

 most enduring sculptures. A curious shrine with a sphinx in the 

 centre cut out of the same block, found in the temple of Turn at 

 the site of the ancient Pithom, near Ismalia, is of this stone. Two 

 large sacrificial tables in the Boulak Museum are of the white 

 variety of the same stone, and are remarkable examples of the 

 working on a large scale of a perfect quartzite. One of the colossi 

 in front of the south propylon of Karnak is a monolith of similar 

 material. Each of six colossi in front of this propylon was made 

 of a different kind of stone, representing quarries in different parts 

 of Egypt, and the one sculptured in this hard and refractory rock 

 shows the bands of flint pebbles cut through and polished, along 

 with the paste which is nearly as hard as themselves. 



The convenient name of "Nicolia Sandstone" has been bestowed 

 on this formation by Zittel. Its relation to the underlying Eocene 

 beds appears in the Section Fig. 1, which also indicates the supposed 

 outlets of hot springs and the horizon of the silicified wood, which, 

 when laid bare by the denudation of its matrix, constitutes the so- 

 called " petrified forests " of the deserts near Cairo. 



Zittel has described extensive areas of Miocene deposits in the 

 Lybian desert west of the Nile, and in the neighbourhood of Jebel 



^ Newbold, Quart. Journ. Geol. Soc. 1848, vol. iv. states the same conclusion, p. 353. 

 ^ Beyrich, Proceedings Royal Academy of Berlin, 1882. 



3 R. Brown, Quart. Journ. Geol. Soc. iv. Carrutliers, Geol. Mag. Vol. VII. 

 p. 306. linger and Schenk, — Zittel, Lybischen Wuste. 

 * Schweinfurth, Proc. German Geol. Soc. 1883. 



