(57 ) 



polder was i)reseiil in il already liflv years a^io", if 1 may consider 

 water that eoiilaiiis 200 to 300 and even more miili<i,rammes ol" 

 chlorine per litre as fresh-water, as I nnderstand he does. Only with 

 this latter not common qualification one is entitled to say that nnder 

 the Haarlemmermeer pokier the dihninni has on an a\'era,t>,'e inore 

 than 10 metres fresh-water, for tiie orcater part of that polder has 

 110 fresher water in its undergronnd than with these amonnts of 

 chlorine. Oidy where the higher gronnds are ch^iily of recent origin 

 this is ditferent, for the rest the watei' in the nppcr dihixial layei'S 

 of the Haarlemmermeer polder contains about the same amount of 

 chlorine as the water of the formei- lake. Of the Wilhelmina s|)ring, 

 the amoinit of chlorine of >vhich is over oOOO milligrammes, the 

 depth is unknown ; nndonbtedl}' ho\\'e\'er it goes down as far as 

 the salt water which in most ])laces of this ])ol(ler is to he found 

 below 40.50 metres. 



The most serious difticully opposing my \iew of the origin ot 

 the fresh-water in the subsoil of some shallow polders is not men- 

 tioned by Mr. dk Ukuyn. It is that the tVesh-u atei- in (|uestion in 

 all seasons not oidy is surrounded by, but also rests ou and is 

 covered by brackish water. How can the fresh-water under these 

 circumstances owe its origin to the rain fallen on the brackish 

 u|)[)er ground ? 



The ex[)lanation of this paradoxical phenomenon 1 mean to ha\t' 

 found in the peculiar hydrological condition of those polders which, 

 like those between Amsterdam and the Haarlemmermeer ])older, are 

 themselves at a level only little below A. P. and arc situated jiear 

 deeper drainings. In a similar condition are the shallow polders near 

 Purmerend and Schermerhorn. Like here towards the Haarlemmer- 

 meer i)older, so yonder towards the deej) [)olders Purmer, Wijde 

 Wormer, Beemster and Schermer, a considerable flow exists in the 

 coarser diluvium luider the more compact alluvial cover and at 

 the same time a vertical downward movement, Avhile in those dee|)er 

 polders the water tries to rise through the alluvial cover which forms 

 oidy an imperfect screen. Consequently in boring-tubes the ground- 

 water from the diluvium in these latter rises higher than the field, 

 wliereas in the shallow polders it remains far under it and below 

 the level of the grouiid water. These ^circumstances aiid the geological 

 condition of the soil form iji my opinion the solution of the riddle 

 of the presence and the permanence uudei- some shallo\\- polders 

 of fresh-water which on all sides is surrounded by bi-ackish water. 

 I arrived at this conclusion especially by studies in the Rieker polder 

 near Sloten, iji which the source for.the military. water-su[»[)ly ïqv 



