( 55 ) 



al)oii( llic middle of \\\v IS"' ceiilurv deserilies the water of tlic 

 Jlaai-lem Lake as "tVesli, luit iii sonic places, wliere the <>roiin(ls 

 become brackish, as near Siooten and towards Amsteldam, tlie water 

 of the lake is sometimes of a sallish taste, lliit the abundance 

 of water fj-onj the Ivhiiie and (he snpply from so many small 

 lakes and waters \\liicli discliariic tliemsehes into il, brins; abont 

 that the brackish \vat(M- can by no means ,i>et the npper hand, 

 and so the lake has on tlu^ a\ hole «^ood fresh-waler." Aleanwhile 

 a qnantity of salt amonntin^i»- to 300 milligrammes pei' liti-e is 

 according to the latest investigations jiot nn|)alatable. An analysis 

 by G. J. Mri-üKR ') of water taken IVom the lake near Sloten 

 in Noyember 1825, shows that il contained 3113 mg. chlorine ])er 

 litre. Now this is the season dnring which it will probably have 

 been least brackish. Hence it is im|)i-ol)able thai the water of the 

 Haarlem Lake was on the whole really fre.'^i. Indeed, the lake had 

 ample opportunity to receiye salt from the I.l (which had already 

 become salt towards the middle of the 13"» centnry) throngh the 

 npper gi-onnd of the polder-land which consisted chietly of fen and 

 which separated the two waters in jdaces (near Halfweg) like a 

 trne isthmus. It is also known that at any I'ate towards the middle 

 of the 18"' century those grounds under \yhich fresh-water is found, 

 were brackish. Yet fresh-water of a much eai-liei' period might in 

 places have remained in the underground. Water derived not only 

 trom the north and Avest sides, but also from the east, may have 

 liltered into the polders mentioned at the north-east of (he present 

 Haarlem Lake. The Amstel certaiidy contained for centuries perfectly 

 freshwater, derived from the Rhine. As late as 1530 the Amsterdam 

 canals, fed by this river, had drinkable water, bnt soon this supply 

 was gradually more and more reduced by natural causes. 



Is now the motion of the groundwater, not only in the finer 

 alluvium, containing much sand, but even in the coarse and gravelly 

 dilu^•ial sand, which transmits water much more easily, really so 

 slow, as Mr. de Bruyn belieA'es, that in three or four centuries the 

 intluence of the altered cii-cumstances as to level and composition 

 of superficial watei's on the deep groundwatei' will scarcely be 

 perce}»tible? I believe that numerous facts, of which I will mention 

 a few in this communication, are at variance with this o[)inion. 



1) G. J. Mulder. Verhandeling over de wateren en lucht der stad Amsterdam, 

 p. 66. Amsterdam 1827. LoraK, quoting from second hand, wrongly mentions this 

 same analysis under two different lieadings and with diflerent amounts of CI. 

 (Onze brakke, ijzerhoudende en alkalische bodemwateren, Verhandelingen der 

 Kon. Akad. 2e Sectie, Dl. 6. N". S. 1899. p. 9). 



