250 mr. a. wade ok the [May 1911, 



IX. Origin of the Sand. 



With a view to discovery, if possible, of some clue to the origin 

 of the sand on the desert and in the hills, I examined a series of 

 samples from various localities. One series was especially collected 

 from the shore, one from the centre of the plain, and one from the 

 gullies in the hills. 



Prof. Walther, 1 in his work on the physiography of this desert, 

 says that the chief source of the sand is the granite area. Barron 

 & Hume ~ disagree with this, and claim the Nubian-Sandstone areas 

 as the source of origin. They do this, not on account of the 

 mineral composition of the sand, but because of the abundance of 

 sand in those areas and its absence in the midst of the granite 

 hills. They specifically mention the tract that I examined in detail, 

 as being one towards which the sand is being continually blown 

 from a Nubian-Saudstone area. This may account for some part of 

 the sand present along the eastern side of the Mellaha-Esh ranges, 

 but the microscope does not, in the main, support their contentions : 

 it rather justifies, indeed, Prof. Walther s statement. I append the 

 results of microscopic examination of four samples of sand, the last 

 of which was taken from the base of a Nubian-Sandstone escarpment. 



No. 1 Sample. — Salt-caked sand from the western shore of the Gulf of 

 Jemsa, consisting of large rounded grains mingled with very fine 

 particles of dust, made up chiefly of fairly angular quartzose material. 

 The large grains are well rounded, and include quartz, pink felspar, 

 some cream-coloured felspar, and a little green epidote. Flakes of 

 biotite are common: they are somewhat altered, and present a very 

 metallic appearance. More angular grains or tiny flakes of a black rock, 

 resembling the dark andesitic rock of the hills nearest the shore, and 

 one or two subangular fragments of a purplish-brown rock were present. 

 A few tiny needles, probably of apatite, occur also, as well as some 

 tiny rhombs showing a faint, high refractive index and assuredly not of 

 an isotropic mineral. These latter are almost certainly dolomite. The 

 biggest grains observed had a diameter of 2*5 mm., though 1*5 mm. was 

 a more usual size. 



Foraminifera are fairly plentiful, forms apparently assignable to 

 Botalia and Textidarla being discernible. 



No. 2 Sample. — Loose sand filling a watercourse, half a mile from the shore. 

 This sand was much finer throughout than that of Sample 1. The 

 same abundance of well-rounded pink felspar is present, with much 

 colourless quartz. Very many dark and even black grains are present, 

 some of which are slightly magnetic. An altered brassy-looking mica 

 occurs here in tiny flakes. 



No. 3 Sample. — Obtained near the foot of a gully in the hills, about a mile 

 west of the Gulf of Jemsa. 



Here the grains vary greatly in size. They range in diameter between 

 075 mm. and the finest dust. The sand contains all the minerals 

 observed in Samples 1 & 2, together with small angular flakes of the 

 black rock measuring up to 1 cm. in diameter. Here, again, the pink 



1 ' Ueber Ergebnisse einer Forschungsreise auf der Sinaihalbinsel & in der 

 Arabischen Wiiste' Verhandl. Gesellsch. f. Erdkunde Berlin, vol. xv (1888) 

 p. 244. 



2 Op. cit. Egypt. Geol. Surv. Rep. 1902, p. 288. 



