to Ground Water along Coasts. 



285 



several other factors, including the tides, (see p. 280), the 

 permeability and structure of the rocks, the amount of 

 fresh water supplied by rainfall, the density of the sea 

 water, and perhaps the prevailing temperature. As has 

 been shown by Herzberg and others, the depth of the 

 contact below mean sea-level is, in uniform material, a 

 function of the height of the water table above sea-level. 

 The simplest case that can be assumed for considera- 

 tion is that of a small island composed of uniformly por- 

 ous sand. The probable movements of ground water and 



Fig. 4. 



Fig. 4. — Ideal diagram showing movements of ground water and grada- 

 tion into sea water along shores composed of uniformly porous sand. A, On 

 a small island: B, on a mainland shore. 



the gradation from salt to fresh water on such an ideal 

 island are illustrated in figure 4 A, which shows the 

 approximate form of curve given by Herzberg for the 

 island of Norderney. Imbeaux 10 states that the form 

 of curve which he obtained experimentally closely 



10 Imbeaux, E. : Les nappes aquif eres au bord de la mer ; salure de leurs 

 eaux, Bull, des seances de la Societe des sciences de Nancy, ser. 3, t. 6, pp. 

 131-143. 



Am. Jour. Sci. — Fifth Series, Vol. IV, No. 22. 

 19 



-October, 1922. 



