G. W. Grahham—Welh of North-Emtern Sudan. 313 



above the place where sample II was taken. The well-water contains 

 rather more solids in solution, and is, as a rule, rather harder than the 

 water from the stream-bed. The analysis of samples from this valley 

 has extended over a period of about a year, and it has been found that 

 the composition of the water is little subject to variation. Isolated 

 samples, it is true, have given markedly different results, but these 

 may be due to a variety of causes and do not aiFect the conclusion. 



VII and VIII are analyses of water from wells in smaller valleys 

 to the south-west of Port Sudan. They contain very much larger 

 quantities of salts than those from Khor Arbat, and, as the drainage 

 areas are composed of similar rocks, it appears that the difference in 

 composition must in some way be due to their relative sizes. The 

 smaller areas receive less rainfall and are more affected by 

 evaporation. 



The next three analyses are from wells on the seaward margin of 

 the Maritime Plain, in the vicinity of Port Sudan and within about 

 2 miles of the sea. Though analyses IX and X show large quantities 

 of salts, they do not represent such saline waters as those of the 

 small rock valleys, while the composition of the sample from Eencini's 

 well is quite comparable with the Khor Arbat analyses. Gypsum 

 deposits do occur associated with those of the Maritime Plain, and, 

 tliough none are known in the vicinity of these wells, perhaps the 

 high content of sulphates may be accounted for in this way. The 

 ' Far Well ', to which the last analysis relates, is situated about 

 5 miles from the sea, and is intermediate in position between the rock 

 valleys and the shore. It consists of two shafts with a gallery between 

 them, and a constant quantity of water is pumped as a temporary 

 supply for Port Sudan. The figures show rather a high content of 

 chlorides as compared with the sulphates. 



The analyses show that the underflow of the Maritime Plain is 

 derived from sources widely different in quality. The underflow from 

 the Valley Pill contains large quantities of salts, but it must be con- 

 siderably diluted by the purer flood- water and local rainfall. It is 

 therefore not surprising to find some of the wells near the sea yielding 

 a less saline water than those of some of the rock valleys. A boring, 

 made at a point about IJ miles south-west of the ' Far Well ', traversed 

 the deposits of the plain to a depth of 1100 feet. Both here and in 

 the shallower boring at the ' Xear Wells' it was found as a general 

 rule that better water was obtained in the coarse-grained deposits than 

 in the finer muds and sands. The quality also varies with the depth, 

 and the best water is found at the surface of the zone of saturation. 

 In the deep boring some improvement was found towards the limit of 

 depth attained, but the quality of the water was not satisfactory, and 

 the attempt to obtain a supply in this way was abandoned. 



The deposits of the Maritime Plain are mainly submerged below 

 sea-level, and the laws governing the flow of water in them offer an 

 interesting problem, but at present the data are insufiicient to enable 

 us to discuss it. The greatest flow appears to occur on the surface of 

 the zone of saturation where the best waters are found, but it does not 

 seem possible to say how far the water beneath is to be regarded as 

 stagnant. The rate of flow also depends on the nature of the deposits, 



