( 5:! ) 



of' iO M'' of IVcïsli walei' per M% t'oi-respoiidiiii; (o '/,, to 74 ^^'^^'^ 

 between the grains of «and over «i Ihic-kiiess of 30 to 40 metres. A 

 consumption of 50 million 1\P per year being suflicient with the 

 existing dune-water conduit for the need of the popnlation, taking 

 its increase into acconni, this ((uanlily would be able to supi)ly water 

 for a Iiundred years ; now we may pi-esume that in a hnndred years 

 science will have so much advanced that it will be practicable then 

 to convert any water into snitable (lriid<ing-water. 



The answer to onr question must in my opinion be affirmative as 

 Avell as negative. Aflirmative with respect to snpplying water to single 

 dwellings, to a village, or to a temporary supply in war-time such 

 as the Engineering Corps has made at Sloten ; negative with respect 

 to a lasting demand on a large scale and this because in practice 

 pecuniary considerations wonld force us to withdraw the water from 

 a limited surface which wonld be impossible ^^ithont causiug such a 

 diminution in pressure that certainly with a lateral afUux also water 

 from below would flow to, so that after some time lu-ackish water 

 wonld be obtained. 



Hence Prof. Dubois' assertion, that a snfticient quantity of drinking- 

 water is and remains avaUable in the ground nnder the shallower 

 poldei'S, is in my opinion entirely wrong. 



Geology. — "(l/i the orui'tn of tJic firsh-frafcj' in tin' sahso/'/ of d 

 fern sh/flloir poI(/('rs'\ By Prof. Eug. Dubois. Communicated 

 by Prof. Bakhuis Roozeboom. 



(Communicated in tlie Meeting ot November 28, 1903). 



In the meeting of the Academy of September 26 ult. Mr. H. E. 

 DE Bruyn, althongli he agreed with most of the principal conclusions 

 about the origin and the direction of motion of the groundwater in 

 part of our lowland, contained in my comnumication to the Academy 

 of June 27, gave an elaborate exposition of the grounds on account 

 of which he cannot accept my conclusion concerning the origin of 

 the fresh-water in the subsoil of a few shalloNN polders, in my opinion 

 this has to be sought in rain, fallen on the spot or at a relatively 

 short distance, \vhich Mr. \)V. Bhuvn thinks inq)ossible on account of 

 considerations about the amount of the afflux in the Haarlemmermeer 

 polder which, iji his opinion proves that Ihe layers above the diluxium, 

 especially the "old sea-clay" transmit water (o a nuich smaller extent 

 than is necessary in my representation. He also supi)oses that part 

 of the fresli-water which was present under our polder-land a thou- 



