314 Q. W. Grahham— Wells of North-Eastern Sudan. 



and, as these differ, the movement near the surface is not everywliere 

 the same. The striking differences in composition shown by analyses 

 IX, X, and XI, all relating to wells within about 2 miles of the 

 sea, may be accounted for partly by the extents to which the different 

 wells are used, and partly by the nature of the deposits from which 

 the water is derived, whether fine or coarse grained. I have not 

 visited these wells, but I understand that both those of Bencini and 

 Simon Lingo are in ' conglomerate ', and that the ' Far Well ' is in 

 similar material. The general opinion is that the best water is derived 

 from this ' conglomerate ' as opposed to the finer-grained beds. The 

 concentration of salts in finer-grained deposits appears to be a 

 phenomenon of fairly common occurrence, and some of the principles 

 developed by Mr. E. C. Sullivan ^ in connection with the deposition 

 of ore may account for it, but my knowledge of his work is at present 

 only derived from a review kindly shown me by my colleague Mr. Dunn. 

 It is pointed out that if a solution is filtered through a soil the first 

 part of the filtrate is less saline than the original solution, a proportion 

 of the salt remaining behind in the filtering medium. The effect 

 increases with the fineness of grain of the filtering medium, and 

 appears to be due to the different rates of diffusion of the constituents 

 of the solution. This principle would account for the existence of 

 more saline waters in the finer-grained parts of a deposit, and suggests 

 the possibility of these being obtained when the normal underflow is 

 disturbed by a well. 



The existence of wells such as Bencini's, yielding a comparatively 

 good water, has led to attempts at obtaining larger supplies by means 

 of pumping. This implies deeper wells, greater lowering of the water- 

 table, and, in consequence, a more saline water is yielded. The analysis 

 of a sample taken from this well in April, 1908, showed only 318 parts 

 per million of solids in solution (W.K.L., Khartoum), while in samples 

 taken since that to which analysis XI relates, and collected after 

 periods of bailing, the quantity was found to have increased to 1110 

 parts. A sample from Simon Lingo's well, taken in September, 1908, 

 showed 1440 parts of solids per million (W.R.L., Khartoum), but, as 

 a result of deepening and increased pumping, the water became more 

 saline, and was found to contain, as shown in the accompanying table, 

 no less than 2573 parts of solids, and this only a month after the 

 former sample was taken. The ' Tar Well ' is said to have yielded 

 a better water at first, but, as a result of continual pumping, the 

 water has become more saline, and now appears to maintain approxi- 

 mately the composition shown in the analysis. 



Capt. H. H. Kelly, B.E., to whom I am indebted for much of 

 the information about the wells in the neighbourhood of Port Sudan, 

 considers that, in some cases at least, the wells are of considerable 

 antiquity. They have evidently been made by people with a know- 

 ledge of construction that the present natives, the Hadendoas, do not 

 possess, and his discovery of a Roman coin in one of thekhors where 

 these wells are situated in a measure confirms his conclusion. 



Before leaving this area, where the detrital deposits of the Valley 



1 U.S.G.S. Bull. No. 312, 1907. 



i 



