Vol. 67.] EASTERN DESERT OF EGYPT. 241 



IV. The Sandy ' Gravels.' 



\Ykere the ridges and mounds touch the coast-plain, there is an 

 abrupt change in slope as -well as a change in the formation. The 

 plain shelves gently oft' towards the sea; and, although it is covered 

 with loose stones and angular boulders derived from the material 

 of the mounds, there is a predominance of sand, which increases 

 seawards until nothing remains but the sands of the shore 

 impregnated with salt or gypsum. The 'gravels' in which the 

 sand predominates largely are very different, both in structure 

 and in origin, from the igneous ' gravels ' with which I have 

 just dealt. They owe their present characters largely to the action 

 of rain and storm waters upon the mounds of coarser material 

 and upon the hills themselves. They are, in fact, formed by the 

 overlapping of ordinary fan-taluses originating in the numerous 

 wadis which cut through the hills. This is beautifully shown 

 under the wadis cutting through the Jebel Zeit range, where these 

 fan-taluses reach huge dimensions and are almost perfect in their 

 outlines. These sandy ' gravels ' are intersected in almost all 

 directions by a network of watercourses (PI. XIV, fig. 1). There 

 is, of course, a distinct rise in level opposite the mouths of the 

 wadis — contrasting with the behaviour of the coarse ' gravels/ 

 which are cut away or altogether absent. 



Where the watercourses have formed a cliff like those seen some- 

 times in the mounds, a distinct bedded arrangement is observable, 

 which is never seen in the ' gravel '-cliffs. Such a cliff is to be seen 

 in the mouth of the large unnamed wadi south of the Wadi 

 Mellaha. The arrangement is of the nature of current-bedding ; 

 but this structure was shown on a large scale in shafts and 

 trenches made in the material of the plain itself. In these the 

 beds of pebbles varied greatly in thickness, from little strings of 

 small pebbles to coarse beds of pebbles and sand a few feet thick. 

 The bedding-planes were sometimes marked by a more perfect 

 cementation of the sand-grains, causing the lines of bedding to 

 stand out from the sides of the section after it had been left some 

 time. The sand was loose and imperfectly consolidated throughout. 

 The mode of origin suggested by Lomas 1 for some at least of the 

 Triassic current-bedding is here demonstrated. The old channels 

 are filling with sand ; in some cases they are completely filled, and 

 so, during the next rainy season, the new channels may take 

 courses which differ in position, in depth, or in both from those 

 which existed before. 



V. Parallels nr Trias and Permian. 



Parallels to nearly every feature described can be seen in the 

 Bunter Beds. The masses of pebbles with comparatively little sand 

 found in the Midlands : the sand with pebble horizons sometimes 

 only a few inches thick, sometimes increasing to 3 or 4 feet in 



1 Proc. Liverp. Geol. Soc. vol. x, pfc. 3 (1906-1907) p. 175. 



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