RevicKS — Dr. Hume's Geology of Egypt. 79 



III. — Geology of Egypt. 



T N an essay on "The South-western Desert of Egypt", published 

 J_ in the Cairo Scientific Journal (vol. ii, August and September, 

 1908), Dr. "W". F. Hume gives some account of the progress of the 

 Geological Survey of Egypt since its establishment in October, 1896, 

 and of the problems that remain to be solved. Already it has been 

 possible to prepare a general geological map of the country, despite 

 the fact that there have never been more than five workers in any 

 one year, and that in many cases they have had to construct their own 

 topographic maps. Naturally there is much yet to be done before 

 even the general picture of the geology can be satisfactorily completed. 



Among areas at present unsurveyed in detail is the great South- 

 western Desert, beyond Dush in the Kharga Oasis, and in the present 

 essay Dr. Hume gives the results of an expedition undertaken with 

 the object of ascertaining the nature and trend of the rocks, the 

 movements by which they have been affected, and their economic 

 resources. 



The Fundamental Strata comprise granites seamed by dykes of 

 dolerite and felsite, gneisses, and schists, and these are overlaid by 

 thick beds of Nubian Sandstone, which contain materials derived 

 from the destruction of the older crystalline rocks, in the shape of 

 coarse pebbles of quartz and felspar in the lower portions and white 

 sands in the upper. The still newer strata comprise the Carapanian 

 and Danian of the Upper Cretaceous and tlie Libyan Beds of the 

 Lower Eocene, the succession agreeing with that observed elsewhere 

 in Egypt. 



Attention is drawn to evidence of considerable movements resulting 

 in almost symmetrical oval basins or centroclinal folds. The Funda- 

 mental Strata which are at or very near the surface " have very 

 definite relationships, both to the centroclinal basins of the sedimentary 

 strata and to the bends in the cliff-wall of the plateau, these all lying 

 along definite lines, trending east and west". Thus " it will be noted 

 that the rectangular bends of the plateau, the granitic masses, and 

 the centroclinal basins of Eocene and Cretaceous rocks tend to fall in 

 definite lines, the granitic masses surrounded by the dipping sandstone 

 being the domes, and the Eocene-Cretaceous exposures being the basins 

 due to the double movement". 



Referring to these movements of upheaval, Dr. Hume remarks that 

 ** when such folds take place the convex portions or anticlines first 

 become subject to erosion by the sea as they tend to rise above the 

 waves, the elevation and denudation being probably simultaneous". 

 In this way the origin of tlie depressions through subsequent erosion 

 of the softer strata, and their influence on the formation of oases, are 

 discussed. The smaller oases occur, in the main, at the junction of 

 the hard and practically impermeable limestone of the Campanian 

 with the white limestone of the Danian ; while the greater oases are 

 found in the underlying Nubian Sandstone, the water being upheld 

 by clayey layers which are intercalated in the strata. 



