260 MR. A. WADE ON THE [May I9II, 



XII. Summary and Conclusion. 



The results of the investigation are briefly as follows : — The 

 * gravels ' of the Eastern Kanges are of local origin, accumulated by 

 the sea under peculiar local conditions. The desert sands in the 

 area are mostly derived.irom rocks in their immediate vicinity. 



Dolomite rhombs are present in recent marly deposits formed 

 under actual desert conditions. 



Sand plays a part, apparently not hitherto observed, in the dis- 

 integration of rocks. It acts as innumerable wedges along joint- 

 planes and cracks. 



llecent calcareous deposits are converted into gypsum, with 

 destruction of organic structures. 



Sodium carbonate and epsomite are common as encrustations 

 among the raised-beach and coral-reef deposits. 



The age and distribution of the older salt and gypsum deposits 

 are considered. It is suggested that the beds are contemporaneous 

 with those of the Fayum, that is, are of Oligocene age. Close 

 comparisons are possible in certain cases between the formations 

 considered and those of the British Trias. The geology of the 

 islands at the mouth of the Gulf of Suez is shown by means of a 

 sketch-map (fig. 4, p. 255). 



In conclusion, I have to acknowledge much valuable assistance 

 from Mr. S. Tl. Illingworth in connexion with the chemical work 

 done in preparation of this paper. To him my best thanks are due, 

 as well as to my former pupil, Mr. Ewart Mather, who kindly 

 made a check-analysis of the saline sand. Especially do I owe 

 thanks to Prof. W. W. Watts, F.R.S., for much kindness both in 

 reading through the paper and in making suggestions with regard 

 to it. 



EXPLANATION OF PLATES XIII-XVI. 



Plate XIII. 



Gully in the Um Esh range, showing the gap between the ' gravel'-terrace 

 and the main hills. The head of the gully is filling with sand. 



Plate XIV. 



Fig. 1. View from the summit of a ' gravel '-terrace : the plain is seamed with 

 radiating watercourses. In the distance are seen the salt-covered 

 sands and the Gulf of Jemsa. 

 2. Limestone almost entirely fretted away by wind-blown sand, north 

 of Jemsa. 



Plate XV. 



Fig. 1. Coarse sand with miniature dreikanter, from the plain between the 

 L T m Esh and the Jebel Zeit ranges. Natural size. 

 2. White limestone-cliffs on Jubal Island, illustrating the effect of wind- 

 blown calcareous sand upon joint-planes. The projecting fossils show 

 the dip of the strata. 



