Vol. 67.] EASTERN DESERT OE EGYPT. 251 



felspars are among the best rounded of the grains, while the black grains 

 are very angular. Wind-carried foraminifera are present in this sand. 



On treating the sand with acid, I found that some calcareous particles 

 are present. I also found in this sand some purple grains, which are 

 probably derived from the porphyries of the Mellaha range. 

 No. 4 Sample. — Sand from the base of the Nubian-Sandstone escarpment, 

 Zeit rauge. 



This sand consists almost entirely of colourless quartz-grains. Some 

 cloudy grains occur, which probably are milky quartz. A few grains of 

 somewhat altered mica are seen. The sand is more purely quartzose 

 than any of the other samples. The grains are rounded to subangular, 

 and are fairly even in size. 



A noteworthy feature is the way in which the felspars are 

 rounded into sand-grains. The dry disintegration seems to result 

 in very little chemical alteration, the effect being almost entirely 

 physical. As a result, felspar is a common constituent of these sands. 



I have already shown that the big sand-grains found in the 

 desert between the Um-Esh and the Zeit ranges are derived from 

 every type of local rock, and are intimately connected with the 

 'gravels* in composition and in origin. 



It thus appears that the sands along this belt, at any rate, are 

 in the main derived from the break-up of the local rocks : including 

 chiefly the granite, and to a smaller extent the andesitic rocks and 

 porphyries. The granite, where exposed, can be seen in all stages 

 of decay. Instead of breaking down into flakes, it crumbles away 

 into coarse material, which is readily picked up by the strong winds 

 and soon worn down into sand-grains. It is certain, however, 

 that the Nubian Sandstone does supply some part of the material, 

 although it does not appear that such material predominates. 



X. Salt and Grrsuir. 



In studying these deposits, it is best to deal with them under 

 two heads : — 



(a) The deposits now in process of formation. 



(6) The older deposits, such as are found in borings or in outcrops at 

 the surface. 



(«) The first type of salt-deposit was best seen in process of 

 formation on the western side of the Gulf of Jemsa. At this place 

 the gulf is bordered by a shallow depression, very little above the 

 highest tides that we observed. The depression runs in a series of 

 crescentic outlines for a considerable distance along the coast. It 

 is filled with a deposit of snow-white salt crystals to a thickness 

 in places exceeding 1 inch. This deposit was evidently due to 

 the evaporation of sea-water which had at some time flowed into 

 it during a higher tide than usual, or had been driven into it by 

 a favourable wind. The hardened saline mud found along the 

 borders of the gulf, and also at the southern end of Zeit Bay, has 

 already been described (p. 245). This occurrence reminds one of 

 the similar phenomena noted in the Keuper ALarls of the Lancashire 



