( 757 ) 



place, tlial wilhiii lliose poldei-s, jiisl as oiilside (lioni, hiil already 

 al a liij2,ii(H' le\eK tlie water deeper down will he found lo iiave a 

 liighei- salt standard. At Hoofddor[» the (pianlity of chlorine, at 

 18.5 M. : A.P., was 202 m.U. a Liter; at 28 lAI. : A. P., 200 m.G. 

 and at 38 M. ! A.P., 993 ni.GJ. With such a rapid increase as in 

 the last 10 M., iinniixed sea-water may he expected, at little greater 

 depth. 



No douht can l)e entertained as to undergronnd sea-\\'ater and 

 fresh Avaler in onr sea-provinces balancing each other in a way, as 

 indicated hy P)AnoN Ohyben and Herzberg ^), xevy much however 

 modified, in general and in special cases, by the general geological 

 structure with its local modifications. There is no ground for fear 

 of the sea-water coming up from belo^v, in ]»art of the dunes, in 

 which the imderground water has been lowered down to the sea- 

 level ; the XGvy fact that there are polders, which already for 

 centuries lie beloAv it, and still have tresh water, down to great 

 depths, and that even of the deepest polders the u))[)er-soil, several 

 scores of metres deep, is much more soaked with fresh than with 

 salt water, refutes that fear. 



Remarkable however is that at Hoofddorp, although situated in 

 the midst of the Haarlemmermeer polder, the deej) underground water is 

 less salt than at Eert-den-Koning, near the edge of the polder, and 

 less still so than some kilometres north-west of Hoofddorp, e. g. on 

 the farm Mentz, where a deep well, [)resuniably eipially deep, has 

 water containing 653 m.G. chlorine a Liter, i. e. 2^ times the 

 quantity of that at Hoofddorp. Differences in the condition of the 

 sub-soil are evidently the cause of those differences in the salt quantit3\ 



In the shallow polders, on account of the direction downward of 

 the \ertical motion, also the water from the canals ("boezemwater") 

 may be the cause of rendering the deep underground water salt, 

 ^vhen locally the structure of the soil does not prevent it. 



Bearing in mind, for the motioji of the umlerground water, the 

 significance of the difïerent heights of the polders, and not forgetting 

 the irregularities in the extent, the thickness and the com|)arative 

 pureness of the clayey beds, also irregularities in the vertical tlistri- 

 bution of the water and in the composition of it may be explained. 



1) W. Badon Ghyben in : Tijdschrift van het Kon. histituut van Ingenieurs 1889, 

 p. 21; Herzberg in; Journal fur Gasbeleuchtung imd Wasserversorgung. 1901, 

 p. 815 s.q.q. I count myself happy to have pointed out in lectures, conversations 

 and letters this forgotten merit of one of our engineering-officers, in consequence 

 of which remembrance Mr. C. E. P. Ribbius and Mr. K. d'Andrimont have, in 

 their publications given due honours to our compatriot. 



