( 52 ) 



20.000 tons of ('hloriiio. Assiimiiif>- tliat wliat is sup[)lied to flicl)Osom 

 bv all tliese causes is more llian half this rough estimate and less 

 than its twofold we get 10.000 or 40.000 tons of chlorine. In any 

 case there is a deficiency amounting to something between 10.000 

 and J40.000 tons which has to I)e ascribed to a su[)ply of sail from 

 a greater depth. When we bear in mind that this will chiefly come 

 from the Haarlemmermeer poldei- and that this latter discharges on 

 the average about 30.000 tons of chlorine and that the supplies 

 mentioned sub 1 — 4 occur there in a small degree, the supply of 

 salt from below at the present time is pretty certain. A quantity of 

 35.000 tons of chlorine corresj)on(ls to that contained in two mil- 

 lion yr. of water from the North Sea. 



The motion of the deep gi-oiunhvater is generally very slow. 



If e. g. we consider how long it would lake water to travel in a 

 laver of sand between two imper\ ious layers from the sea to the 

 Haarlemmermeer polder, which is a distance of liOOO metres, the 

 difference of pressure being 5 M.. if llie permeability i> the same as 

 that of dune-sand, we liud that il wonjil traxcl iti a year (31.557.000 

 seconds) tlu'ouuh a distance of 



81.557.000 X ^ X 0.0000 



— = 10 M. 



9000 



(0.0006 being the rate of filtration ihroiigh 1 M. n\' duiie-sand with 

 a pressure of 1 M. ^). A distance of 9000 M. would consequently 

 require 900 years. 



As to the rate with which the salt water can rise from below we 

 fnid what follows. Assuming that the rise is constant and that under 

 the Haarlemmermerer polder 5 million W. rises aimually, this gives 

 over a surface of 18000 H.A. with a sjiace of ','3 to ' \, between the 

 grains of sand, a rise of about 100 mm. per year; a I'ise of 50 metres 

 would tiieu recjuire a period of 500 years. 



The question now naturally arises: since a large quantity of fresh 

 water is present in the diluvium under our polderland and the salt 

 water flows slowly, is it possible to withdraw this fresh water for 

 drinking-water? The pai-t we are considering has, aftei* taking off 

 the littoral margin and the country louud Anistcrdam which has a 

 different foimation, a surface of about 100.000 H.A. ; not counting 

 the drainages and other less suitable tracts, half of this territory 

 contains 5000 million M\ of fresh water, if we assume an average 



1) Report of the Committee for investigating the supply of water from the 

 dunes to Amsterdam, 1891, suppVment 16, p. 77. 



