( 56 ) 



lil llie lirsl |>]ace llie aclnal facts are iiicoiiipalible willi Mr. 

 i)K l)Krv.\s idea lliat before the draiiiijig- ot' the Haarlem Lake, 

 some 50 years ago, "the direction of the current of the deep 

 groundwater e.g. at Shiten, mnst iiave been exactly the reverse" 

 of what it is now (These Proceedings YI, p. 291) and still less I 

 can assume this for an eai'lier period. For near Sloten the conntry 

 was not lower, but even a little higher than the level of the Haarlem 

 Lake and inx dykctl in. so ihal Ihc inccssaul washing away of the 

 stee|) fenny bank of the lake could be enormously great. According 

 lo an accurate iinesligation. made in 1743, it amounted yeai'ly on 

 the average to as much a> .") lo |0 Kijuland rods (about 19 to 

 o8 metres). It is true thai the upper si<le of the layer of fen which 

 now forms the Ivieker polder near Sloten, lies at 1.35 metres below 

 A. P. (Amsterdam lexel) but its lower side is still on a level with 

 the bottom of the Haarlemmermeer polder, as it formerly was with 

 the boltoni of the lake, and it I'ests on the "old sea-clay". If we 

 now bear in mind Ihal Icn. such a-- lhal of ihe Rieker |iolder 

 ccnisists, when il is completely saliii'aled. for " ,„ of water, as I have 

 found lo l)(' acliially llie case, and ihat morcoxcr the "looseness and 

 shit"tiness" of \\\r>r gionnds which. a> il were, ro.se and sank with 

 ihe water, were well known in the lime of the lake, il is clear, 

 how, afler ihe di'aining. in half a century, by losing over 7s ^^^ 

 their water, they might shrink so far below A. P. and that there 

 can be no (pieslion of an earlier curreiil of the deep groundwater 

 under the llaarh'in lake towards ihc country near Slolen. The lake 

 certainly did iioi allow sncli a current tVom the dunes to juiss under 

 its bottom. 



Though ihe duiio w cic bi-oa<ler and the level of the ^valer in 

 them higher than nowadays, the hydrostatic pressure imparted there 

 to the deep gronndwaler mnsl have been exhansted and the horizontal 

 current stojtped by the water rising in the alluvial co\ er, \vhich 

 forms an imperfect sci-een, long before the opposite side had been 

 reached. For at present the dilference in |)ressure, owing to the 

 waler-pressnre being now 5 metres less in ihe polder than it formerly 

 was in the lake, is certainly not less and yet already in Ihe middle 

 of it oidy a slight u})war(l pressure remains, although [)ressure is 

 directed from all sides to the middle. 



Hence in the niu'ergi-onnd we cmly meet water that soaked the 

 soil from above without any considerable horizontal movement in 

 the nndergronnd. 



I tpdte agree Avith Mr. dk Bkuyn (p. 291) that "part of the fresh- 

 water now i)resenl in the diln\inni under the Haarlemmermeer 



