312 PEOF. E. HULL ON THE GEOLOGY OF THE NILE VALLEY. [May 1 896,, 



to the Nubian Sandstone of Cretaceous age in Arabia Petraea and 

 the Arabah Valley. This, however, is not surprising, considering 

 the distance by which the two localities are separated, and does not 

 afford any evidence that the formations are of different geological 

 ages. In Arabia Petrsea and along the eastern side of the Wadi- 

 el-Arabah, the Nubian Sandstone is distinguished by rich red and 

 purple or yellow colouring; the base is a conglomerate where it 

 rests upon the crystalline rocks, and bands of clay or marl are rare. 1 

 On the other hand, as Lyons has shown, bands of clay are common 

 in the Nubian Sandstone of Upper Egypt, 2 while the prevailing tint 

 is light grey or brown, sometimes slightly tinged with red or pink. 

 It is this stone which was so largely used in the building of the 

 temples, and which has wonderfully resisted the effects of time. 



Part II. 

 6. The Levels of the Ancient Nile. 



The evidence upon which the former greater volume of the Nile 

 waters is inferred may be considered under two heads : (1) the river- 

 terraces now beyond the reach of the highest floods, and (2) the 

 old river-channels through which the waters cannot now pass, 

 owing to difference of level. We shall consider these separately. 



(1) The River-terraces. — In order to arrive at a clear knowledge 

 of the bearing of this subject upon the question of the former 

 volume of the Nile, it may be observed that the general structure 

 of the valley as far as the First Cataract is, on the whole, remark- 

 ably uniform and simple. Pirst, we have the valley itself shut in 

 on either hand by the escarpments along which the plateaux of the 

 Libyan and Eastern 3 deserts terminate; then, from the base of 

 these escarpments there extends, on one or both sides, a slightly 

 sloping terrace, formed of alluvial gravel, sand, or mud, of varying 

 breadth, and terminating along a well-defined bank rising above a 

 lower terrace which, in turn, breaks off along the banks of the river. 

 This lower terrace (No. 1) consists of Nile mud, is richly culti- 

 vated or planted with palms or other trees, and is watered by the 

 Nile inundations. The terrace above (No. 2) is absolutely destitute 

 of vegetation, and its surface, formed of yellowish gravel or sand, 

 contrasts in a striking manner with that of the lower terrace 

 above which it rises. Other terraces at higher levels there may be 

 in Middle Egypt, connected with the epoch of Pliocene submer- 

 gence, 4 of which I shall have to speak presently ; but the above 



1 ' Geology of Arabia Petrasa,' Mem. Palest. Explor. Fund (1886), p. 54. 



2 Quart. Journ. Geol. Soc. vol. .1. (1894) p. 533. 



3 Generally called in the maps ' the Arabian Desert,' because largely in- 

 habited by Arabs, but the name is misleading. 



4 Or during the emergence of the Miocene period, and represented by the 

 caves and terraces at levels of about 500 feet described by Sir J. W. Dawson, 

 ' Modern Science in Bible Lands,' Appendix, 1888, p. 541 ; and Geol. Mag^ 

 1884, pp. 289-92. 



