(46) 



and the Zuiderzee at the north. l)_v tlie rWer Vecht at the east, the 

 Rhine tVoiti Hannelen to Katwijk at the south and the North-sea at 

 the west. 



The geological conditions of this tract inside the dunes are such 

 as are mentioned in the conununicatioir. ujtperiuosi allu\iuin. then 

 prettv generally a layer of' feu (partly disappeared) under which a 

 laver known as "old sea-clay'\ Lender this lattei' the diluvium, 

 consisting to a great depth of sand, coarser and tlner, with here 

 and there hanks of clay which are not continuous however. The 

 "old sea-clay" mentioned is called in the i)aper clay-containing sand 

 and although in my oi)inion also that layer is permeable to water, 

 yet 1 thi]üv its permeability is smaller than Mr. Dlhois assumes and 

 that it is exactly here that the cause of our dilFerence of opinion 

 has to l)e sought. In some i)laces this layer of old sea-clay is wanting; 

 in special cases this makes an investigation \ery difiicnlt, for the 

 general condititni however, which is here dealt with, this circumstance 

 can be neglected. 



The communication consists chiefly of two parts, of facts and of 

 conclusions drawn therefrom. The facts I will pass without comment- 

 ing on them, although occasionally objections might be raised against 

 them or rather against the remarks that accompany them. 



I perfectly agree with a great many of the conclusions, e.g. with 

 the following: 



that in the diluvium fresh water is present to a certain depth: 

 that 'in deeper polders the deep groundwater moves vertically 

 upward, in shallow polders dow-nward: 



that also in the depth a current exists from the dunes to the 

 polders and from the shallower i)oldcrs to the deeper ones: 



that no important continuous subterranean current exists from the 

 higher grounds from the east to the w^est. 



But I cannot acce[)t the conclusion that the fresh groundwater 

 present in the diluvium also in our polders, owes its origin to rain 

 fallen locally or at a relatively short distance during the wet season. 

 In the following refutation of this opinion 1 shall speak of fresh 

 and of brackish or salt w^ater. Of course there is no sharp division 

 between these, but in order to avoid cumbrous definitions I shall 

 make this distinction for simplicity's sake. I base my considerations 

 on tpiantities, but since only their relatixe amount concerns us here, 

 I have rounded my figures as much as possible. 



I intend to sho\v the incorrectness of the conclusion mentioned 

 from the amount of the afflux to in the Haarlemmermeer polder. 

 Xow a paper on this amount by the member of this Academy 



