258 MR. A. WADE ON THE [May I9H, 



stained brown or grey at the surface, and weathered into curious 

 horny protuberances. This is called by American writers gypsite, 1 

 and is actually composed of an aggregate of crystalline plates of 

 gypsum of microscopic size. 



The remarkable effect of warm sea- water upon the gypsum was 

 pointed out to me by Mr. Wells ; and an experiment was carried out 

 by Mr, Sara and myself, in order to obtain some idea of the 

 solubility of the gypsum in sitch circumstances. Two masses of 

 gypsum were treated : — 



No. 1. A mass of 107 lbs. lost 52 lbs. in 5 days. 

 No. 2. „ 117 „ 37 „ 3 „ 



The loss per day in both cases was approximately 10 per cent., a 

 result which explains some physical features connected with the 

 outcrops of the massive gypseous series. 



The common association of petroleum, sulphur, gypsum, and 

 rock-salt found in many parts of the world, as well as in the Red- 

 Sea area, is critically discussed by G. I. Adams 2 in an able 

 manner, though without very definite conclusions, since our know- 

 ledge of the facts is not yet sufficient. 



The age of the gypseous series is difficult to determine, owing to 

 the lack of fossils, though a few imperfect specimens have recently 

 been found in the upper beds. The beds are seen to underlie 

 white limestone of Pliocene or late Miocene age, especially on 

 Jubal Island, where the junction is unconformable : a conglo- 

 merate marks the break. They rest upon beds of Eocene age at 

 more than one locality in the Zeit and TJm-Esh ranges. It thus 

 appears that the gypseous series dates from some part of the 

 Oligocene and Miocene Periods : it is certain that during that time 

 continental conditions prevailed in Egvpt. 



Very few deposits which tend to bridge the gap between the 

 Eocene and the Miocene have yet been discovered. Those of the 

 Fayum in the Western Desert are well known, while these products 

 of the evaporation of a salt-lake or series of salt-lakes which I have 

 been describing may well be their contemporaries in the Eastern 

 Desert. It is significant to note that the very similar gypsum- 

 deposits which exist in Cyprus have also been assigned to the 

 Oligocene Period. 3 



1 F. L. Hess, ' A Beconnaissance of the Gypsum Deposits of California' 

 Bull. U.S. Geol. Surv. 413 (1910) pp. 7 et seqq. 



2 Bull. U.S. Geol. Surv. 184 (1901) p. 49. 



3 C. V. Bellamy & A. J. Jukes-Browne, ' The Geology of Cyprus ' Plymouth, 

 1905, pp. 22, 25. 



