Reviews — Subsoil Waters in Egypt. 323 



British pre-Cambrian sedimentary rocks are included, but Torridon 

 Sandstone might be added ; and towards the other end of the geological 

 scale there is a noteworthy omission of any reference to Grey wether 

 sandstone, while mention might have been made of Coralline Crag, 

 which has yielded building-stone, and of British tufa, which, as at 

 Dursley in Gloucestershire, has also been used for building purposes. 

 It should be noted that the Bargate Stone (pp. 196, 317) is Lower 

 (not Upper) Greensand ; the "Bastard Freestone" of Shepton Mallet 

 (p. 304) is Lower (not Upper) Lias; while on p. 165 Seaton should 

 be Keinton Mandeville. 



Y. — The Movements of the Subsoil Water in Upper Egypt. 



THIS subject is dealt with by Mr. H. T. Ferrar (Ministry of 

 Finance, Egypt, Survey Department Paper JN"o. 19, 1911). As 

 lie remarks, the effects of perennial irrigation in raising the level of 

 the subsoil water, and its influence on health, and on crop-production, 

 owing to the concentration near the surface of injurious salts, are 

 matters of considerable importance. In studying the region the 

 author finds it convenient to describe the wells and other hydrological 

 subjects under the headings of riverain, basin, and desert : areas which 

 form zones parallel to the Nile. Thus, "regarded broadly, the water- 

 table in Upper Egypt behaves as a horizontal plane with flexible 

 edges, which moves up and down as if actuated by an annual tide. 

 The inner flexible edge, which is about one kilometre wide, is the 

 riverain zone. This moves in the manner anticipated, namely, as 

 a plane surface hinged along the side away from the river; but, 

 instead of the hinged edge being on the desert edge, it rises and falls 

 with the rise and fall of the water-plane beneath the basins. The 

 basin zone, or horizontal part of the water-plane, moves up and down 

 almost horizontally, and has an area not greatly less than the area of 

 Upper Egypt which is cultivated. The outer flexible or desert edge 

 of the water-plane, which we will call the desert zone, also moves up 

 and down almost horizontally, but the range of its movement is 

 considerably less than the range of movement of the basin zone." 



The work, so far, has shown that consecutive observations extending 

 over a number of years are necessary to complete the knowledge of 

 the movement of the subsoil water. Experiments at present indicate 

 that "In our so-called riverain zone, the water moves at the rate of 

 150 metres per day at one period of the year, and at other seasons, 

 namely, when the water-table is stationary, it is practically stagnant. 

 The water in the basin zone would seem to have a velocity of less 

 than two metres per day, and that of the desert zone a still lower 

 velocity". Furthermore, "Geological considerations have shown that 

 the subsoil water mingles with the water of the Nile at all times of 

 the year, and that interchange of Nile water and subsoil water takes 

 place continually. In addition to the modifications introduced by 

 geological structure, it has been found that artificial constructions 

 have an influence upon the underflow, and that a quantity of water 

 passes beneath and round the ends of barrages." 



