THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE III. VOL. I. 



No. IX.— SEPTEMBER, 1884. 



CD:Ei,xc^Tj<rjk.Xj j^:rtxcjii,:e:s. 



I. — Notes on the Geology of Egypt.' 



By Professor J. VV. Dawson, C.M.G., LL.D., F.R.S., F.G.S., etc. 

 Principal of McGill College, Montreal. 



II. — Tertiary Deposits Later than the Eocene. 



rilHE mass called Jebel Ahraar or the Ked Mountain near Cairo, 

 JL whose slopes consist of an immense accumulation of quarry 

 rubbish, is composed of hard brown, reddish and white sandstone 

 and siliceous conglomerate. In many parts it has the characters of 

 a perfect quartzite, and appears at first sight extremely unlike a 

 member of the Tertiary series, newer than the comparatively soft 

 and unaltered Eocene beds on which it rests, apparently in a con- 

 formable manner, though its dip to the N.E. is somewhat irregular, 

 and apparently affected by false bedding. The induration of the 

 beds seems to be local, and to be connected with certain fumarole- 

 like openings which have probably been outlets of geysers or hot 

 siliceous springs, contemporaneous with the deposition of the sand.^ 

 Zittel I believe first gave this explanation, which suggested itself to 

 me before noticing it in his memoir. 



This mass is evidently a remnant of a formation at one time 

 extensively distributed in this part of Egypt. This is shown by the 

 fact that silicified trunks of trees, whose natural bed is in the lower 

 part of this formation, near its junction with the underlying Eocene, 

 are found scattered over the surface, not only in the great and little 

 "petrified forests," but at Helouan, and even on the Lybian desert 

 on the opposite side of the Nile. Only the portions locally indurated 

 by siliceous waters have escaped denudation, and it is the irregular 

 appearance presented by these that has given the vague idea of a 

 volcanic origin of these masses to so many travellers. 



There has been much speculation as to the mode of deposition of 

 the silicified wood ;^ but I think the study of it, as it exists in situ 

 at Jebel Ahmar, is sufficient to set them at rest. It occurs in 

 prostrate trunks, sometimes flattened and imperfectly preserved, 

 and sometimes perfectly silicified, and occasionally lying in dis- 

 integrated cuboidal fragments, showing that the wood was imbedded 

 in its natural state and in a decayed condition, and afterwards 



^ See also former article, " Geology of the Nile Valley," pp. 289-292. 



2 Zittel, Lybischen AVuste. 



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



DECADE III. — VOL. I. — NO. IX. 25 



