Vol. 67.] EASTERN DESERT OF EGYPT. 245 



these fine deposits are not of the nature of true marls, but eonsist 

 largely of very fine particles of comminuted quartz, 1 such as cer- 

 tainly form the hulk of desert-dust. The great thickness of the 

 Keuper Marls in Cheshire no longer surprises us, when we see how 

 persistently the dust is at present being blown from the Eastern 

 Desert towards the bays of the Red Sea. The conditions in that 

 sea are not, however, favourable to the accumulation of such thick 

 deposits : for a rapid rising of the sea-bed is in progress, instead of 

 a sinking, which would be necessary for the purpose. 



It is probable that true marls are in process of formation beneath 

 the waters of these bays, just as true marls are found in the Keuper 

 beds in other parts of England. In fact, true marls were found in 

 borings north of the Gulf of Jemsa, as well as among the recently 

 raised limestones on Jubal Island. The materials for the formation 

 of the dolomite crystals observed by Dr. Cullis 2 in the Keuper 

 Marls of the Midland and South-Western districts are present 

 in these muds, since analysis 3 revealed the presence of calcium 

 and magnesium salts in their cementing-materials. A careful 

 search for these rhombs was made in the marls — both among those 

 recently elevated on Jubal Island, and among those which are at 

 present forming on the coasts of the Gulf of Jemsa. The material 

 was first allowed to stand in water for 2-t hours : the liquid being 

 repeatedly changed, in order to get rid of the soluble salts. In the 

 line residue of the marls from Jubal Island, myriads of these tiny 

 rhombs were discovered. They were compared, through the kindness 

 of Dr. Cullis, with those found by him in the Keuper Marls. They 

 were undoubtedly similar in shape and other properties, though 

 somewhat smaller in size. The material from the coast of the 

 Gulf of Jemsa was not so satisfactory, though here again the crystals 

 were present, if in smaller numbers. This interesting discovery of 

 dolomite-rhombs, for the first time in recent deposits under desert 

 conditions, goes far to support the contention of Dr. Cullis that 

 the rhombs in the Keuper Marls were formed by actual deposition 

 from supersaturated waters ; it also furnishes a further interesting 

 parallel between the conditions of deposit in the Triassic sea and 

 those which obtain in the present Red-Sea area. The results of 

 this investigation are important : they tend to show that, although 

 the Keuper Maris of the Midlands and the West of England were 

 laid down under aqueous conditions, those of the Lancashire and 

 Cheshire areas were laid down nearer to terrestrial conditions, the 

 land probably consisting of low-lying areas bordering inland seas 

 or saline lagoons. 



The saline mud on the shores of the Gulf of Jemsa is mostly 

 consolidated, and consists of a hard deposit cemented by means of 

 soluble salts (see p. 252) which are present in a crystalline form. 

 A certain amount of the cementing-material has been re-dissolved, 

 leaving cavities and a honeycomb structure in places. The broken 



1 P. Holland & E. Dickson, Proc. Liverp. Geol. Soc. vol. vii (1896-97) p. 44:j. 

 " Rep. Brit Assoc. 1907 (Leicester) p. 507. 



