G. W. Grabham — Wells of North- Eastern Sudan. 315 



Fill and Coastal Plain play such an important part in the water-supply- 

 conditions, reference must be made to the arid regions of North 

 America, which supply examples of similar conditions. These have 

 been described by Sir. F. H. Newell,' and the underground waters of 

 the Salt River Valley have since been fully dealt with by Mr. Willis 

 Lee.- The Salt River Valley is partly filled with alluvial deposits 

 carrying a large amount of underflow. The valley is much wider than 

 any among the Red Sea Hills, and, as the surface stream-bed has 

 wandered over it in times of flood, filling up the valley, it has left its 

 trace among the finer deposits in the form of boulder-beds and gravels. 

 These boulder-beds have been found to yield the best supplies of 

 water. This, too, is fairly rich in salts, and the town supplies of 

 Phoenix and Tempe both contain over 1000 parts per million of solids 

 in solution, while some with over QOOO parts is successfully used for 

 irrigation. In the light of this we may look forward to a day when 

 the underflow of the Maritime Plain will be utilized in the same way, 

 and more data will be available for the discussion of the pi'oblems 

 connected with it. At present there are gardens at Shata, near 

 Suakin, and small cultivated plots near Port Sudan that show the 

 possibility of using the water in this way. 



Wells in the Nubian Sandstone Series. 



In sandstone regions the wells are no longer dependent on local 

 condition for their water supply. Most of it is probably seepage 

 from the river, and perhaps some comes from distant areas of greater 

 rainfall, but, provided the sandstone is deep enough to contain the 

 water-table, there is no difficulty in obtaining a supply by means of 

 wells. The importance of this series has long been recognized as 

 affording supplies of water, and in Egypt these are tapped in several 

 oases, wliere the water rises under hydrostatic pressure from beneath 

 the overlying beds. In the part of the Sudan under consideration the 

 sandstone is found near the Nile and extends from a little way south 

 of Khartoum to Wa:di Haifa, where it passes beyond the area. In 

 Egypt the Nubian Sandstone Series is overlain by younger beds, and, 

 though these have been found to occur much further south than it was 

 formerly supposed,^ they have not yet been discovered in the Sudan. 



Towards the south, in many places where grazing is good, the 

 natives have wells in the sandstone. These, frequently 200 feet and 

 sometimes even 300 feet in depth, have been dug by them with the 

 primitive tools at their disposal. The presence of Cotton Soil, though 

 it may prevent the local rainfall reaching the water-table, naturally 

 does not interfere with the well supplies. 



The arid regions to the north afford no grazing, and the wells are 

 far apart even on the caravan routes. These generally appear to be 

 situated in hollows beneath the general level of the country, where 

 the water-table is within a few feet of the surface, and have thus been 

 readily found by the natives. Selima Oasis * is probably an example 



1 U.S.G.S., Twelfth Annual Report, 1891, p. 215. 



• U.S.G.S., Water Supply and Irrigation Paper, 1905, No. 136. 

 3 "W. F. Hume, Cairo Scientifc Journal, 1908, vol. ii, p. 321. 



* See Mr. J. Carrie's description [quoted], Anglo-Ecjijptian Sudan, Wymans, 

 London, 1905, vol. i, p. 203. 



