( '59 ) 



Of these wells (!' muy tor IIk^ i)i'eseiit he lel'l out of aceomit 

 since a statiojiarv coiMlilioii has iiul vet established itself in it ; liavinu' 

 its lower end in the clay, the water still rises in i( conlinnally 

 Well IV, 13 again has a higher and varying anionnl (tf chlorine; 

 deterniiiialions at different times gave 114,92,190 nig. jier litre. I 

 believe that this increase and variation of the anionjit of chloi-ine 

 has to be ascribed to the Jieighbonrhood of the deep sail water in 

 relation with (hictiiations in ainiosplieric |>ressnre aii<l also with a 

 [»roi)cr motion of ol)h and Hood of the groinidwaler '). 



In spite of the \ery «-onsideiable raiidall of tli(> latest months, 

 great variations in the percentage of chlorijic di<l not occnr; oidy 

 in aiul Jiear the clay, hejice especially in ('. die amouni of chlorine 

 decreased considerably, in C from (SnO to 7S() mg. jier litre. This 

 resnlt does not verify my formerly stated sn|)|»osition that perhaps 

 during the wet season a coidiniions IVesheniiig of the water might 

 take place. 



Yet I could not agree with the idea that the fresh-water in the 

 subsoil should have stayed there uiulisturbed for at least a few 

 centuries. For why then is fresh-water in the diluxium under the 

 Haarlemmermeer polder and the Lntkemeer poldei- only foinid at a 

 distance not too far removed from the shallow [)olders near Sloten 

 and Osdorp? Why does this layer of fresh-water eiid already l)efore 

 Halfweg, before the Great IJpolder is reached, south of Sloterdijk 

 and also soon eastward of the Amstel? Why does the layei- of 

 Purmerend not extend further than a short distance under the Purmer 

 and Beemster polders? Does not this limitation point to an autochthonous 

 origin of the fresh-water in the underground of the shalloAv polders? 



I tlii]dv to have found the key of the riddle in the stated sudden 

 fall in pressure, amonntijig to more than 1,20 metre, under the clay 

 and tlie deep fen which is a consequence of the fact that the level 

 of the groundwater in the Haarlemmermeer polder is almost 3.5 M. 

 lower than in the Rieker polder. So this compressed deep fen, 

 acting as a semi-permeable wall, can transmit to the deeper layers 

 water, but no salt. 



That fen in a compressed state and under siuiilar conditions of 



') On these influences, especially on llie proper ebl) and flood of the ground- 

 water, see: F. Weyde, Die Abliangigkeit des Grundwasserstandes von dcni Lufl- 

 drucke, dessen Sleigen und Fallen wahrend eines Tages (Flut und Ebbe) , in 

 Meteoj-ologische Zeitscln-ift of August 19(K3. The influence of almosplieric 

 pressure was already pointed out in my former communication. These influences 

 become perceptible only in deep wells, because in them the watei' follows more 

 easily the changing jjressure of the atmosphere and gravity than it does in the 

 nelglibourliuod and so is raised or depressed. 



