pressure as pivxuil in the Rickci' polder, ciii raiise osiiiosis, 1 couM 

 prove experimenlallv willi ap|);uatiis wliieli Mr. A. .1. Stokf, Jr. at 

 Haarlem was kind enoH,i»li to make t'or mo in his workshop and 

 with other apparatus kindly pnt at mv disposal hv Dr. Heringa 

 of Haarlem. The most impoi-tant of these experiments is the follow- 

 ing one. 



In an iroii tid>e of 1 M. length and 154 mm. internal iliameter 

 iiewh duu' fen from the sn|)er(icial laver in the Rieker polder was 

 compressed liy means of a le\er nntil no fiirtluM- compression \vas 

 observed. Tiie pressure was gradnally raised to 2,8 kilogrammes 

 per scpiare centimetre, a pressure erpial to that which is found in a 

 soil of sand or clay at a depth of 14 metres; the layer of fen was 

 three centim. thick. ( )f water, containing a (pianlity of sodium 

 chloride corresponding to an amount of chloi'ine of iOOO mg. per 

 litre, this layer of fen, which on account of its slight thickness, can 

 l)v no means he so perfect a seini-permeahle wall as the deep layer 

 of fen in the Rieker polder which has an a\ei'age thickness of a 

 metre, water was transmitted which contained temporarily at the 

 utmost 750 mg. chlorine per liire: hence at least 250 milligi'ammes 

 were retained. 



Now the deep fen in the Rieker polder occurs as an almost 

 cohei-ent layer, evtending from Haarlem, right through the Haar- 

 lemmermeer ])okler as far as .Mijdi-echt and from Sloten by Amster- 

 dam as far as Zaandam and L'itdam. 'JMiis layer is missed in the 

 north-western corner of the Haarlemmermeer polder, i.e. in the place 

 of the former Lake Spiering and farther south. The lower side of 

 this deep layer of fen lies at about 11 to J 3 metres below A. P. 

 Still deeper at Sloten in some three borings, parts of a second old 

 layer of fen were found and also icpeatedly at Amsterdam and 

 Zaandam. This layer must be distinguished from the former with 

 which it was formerly identified. As a fairly coherent layer this 

 deeper fen can be traced above the dihuium, to the north by 

 Purmerend as far as Hoorn and Enkhuizen, to the west by Wormer- 

 veer, Beverwijk, and Velzen to IJmuiden. The upper one of these 

 deep layers of fen can i-each a thickness of about 1 .M., the lo\ver 

 one is rarely \'.^ metre thick. 



So we may understand how the undergi-ound may have derived 

 in former times and may still derive its fresh-water from the up|»er 

 o-round although this latter alwavs carries l)rackish water itself. 



But will the "layer of clay" which is 7 ^1. thick be permeable 

 enough to render it possible that in the half century, elapsed after 

 the draining of the Haarlem lake, under the polders to the iu)rth- 



