316 G. W. Grahham—Welh of North-Ensteni Sudan. 



of this, and, though Capt. Lyons ^ has suggested that its existence is 

 related to folding, I do not see that this would affect the level of the 

 water-table unless the clay beds in the series are more extensive than 

 is supposed. 



The construction of the railway from Haifa to Abu Hamed led to 

 well digging in the Nubian Desert, and Mr. Dunn tells me that good 

 supplies are obtained in the sandstone at a depth of about 100 feet 

 at No. 4 and No. 6 stations. The famous Murrat wells, close by, 

 have not yet been visited by geologists, but from other accounts they 

 appear to draw their water from Valley Fill among crystalline rocks, 

 and are perhaps just outside the sandstone area. If necessity arises, 

 I have no doubt that successful wells could be made all over this arid 

 sandstone area, both east and west of the Nile, and in many cases, like 

 those already made on the railway, the water would be found at no 

 great depth below the surface. 



The composition of the waters may be illustrated by the following 

 analyses which have been published by Mr. Lucas ^ : — 



Analyses expressed in parts pee Million. 



(a) Alkalinity to phenolphthalein calculated as sodium carbonate, 

 {b) Alkalinity to methyl orange, less that due to sodium carbonate, calculated as 

 sodium bicarbonate. 



I. No. 6 Station. Contains also Si O2 27-2, Fe, O3, and AI2 O3 13-2. 

 II. Bir Adiela. 



III. Selima Oasis, north well. 



IV. Selima Oasis, west well. 



From these figures it appears that the waters vary considerably in 

 the amounts of salts they contain, but they all show a good deal of 

 alkalinity. At Selima there are deposits of salt extensive enough to 

 be worked by the natives. The presence of water so close to the 

 surface must lead to a large accumulation of salts by tlie evaporation 

 of moisture drawn up by capillary action. A marsh is said to exist 

 now, and, no doubt, a small rise in the level of the water-table would 

 convert this into a lake ; sheets of water would also appear in other 

 places where only shallow wells exist now. Evupoi-ation would soon 

 concentrate the salts, and it is quite possible that deposits may have 

 been formed in this way. Travellers have reported many bitter wells 

 in the vicinity, and it is not surprising that these waters, in most cases, 

 contain larger quantities of salts than do the artesian ones of Kharga, 

 in which the quantity ranges from 430 to 470 parts per million.^ 



Another point of interest is the presence of large quantities of 

 nitrates in some of these waters. A sample from Nahud, analysed 

 by Dr. Beam, was found to contain no less than 6-5 grams per litre 



^ Q.J.G.S., 1894, vol. 1, p. 539. 



• Chemistry of the River Nile, Cairo, 1908, pp. 72, 74. 



•^ H. J. L. Beadnell, Geol. Mag., 1908, p. 105. 



