( 62 ) 



15 cm., under ca pressure of HO cm. tiaiisiuitled no less water than 

 a laver of (lie same compressed clay of oidy 4 cm. tliickness. ('al- 

 cnlations like those on page 21)4 of ^Ir. dk Brlyn's communication, 

 in which the rate of filtration through IIOOO M. sand from the dunes 

 is simply assumed to l)e Vao.m <»1" ^'jc ^"^^^ found in an experiment 

 with 1 M. of tiie same sand lead consecpiently to erroneous con- 

 clusions. I also want to |)()int out that in the coarse diluvial sand 

 which forms tiie princi|)al way for the horizontal movements of the 

 water, the velocity of motion is about ten times as great as in 

 sand from tiie dnnes. 



Uiuler these circumstances 1 heHe\e to he jnstilied in maintaining 

 my opinion that the \\ atei- in the iiiidcrgroiuid of some shallow 

 polders is of autochllioiioiis origin. 



It is also clear now, how in many places in the Haarlemmermeer 

 polder water can s])ring up w liich is as fresh as water from the 

 dunes. So in the farm "het Botervat" on the Y road near the Kruis- 

 weg ; in it 1 found as well in the driest |)erio(ls as after much rain a 

 quantity of chlorine of 35 to 37 mg. j)er litre, whereas in the same 

 farm a well has been bored reaching Just below the deep fen, in 

 ^vllich the water coidains an amount of chlorine of 235 mg. per 

 litre. At numerous other spots of the Haarlemmermeer |)older the 

 presence of fresh-water in wells (which j)roved to be no rainwater, 

 as I believed for some time) could be stated; it is also found at 

 about one kilometre east of the just mentioned farm, besides on the 

 Kruisweg between the Sloten road and the Sloler Tocht, on the 

 Sloten road near the Slaperdijk. On the other hand the water in 

 \vells in the north-western i)art of that polder, in which the deep 

 layer of feji is entirely absent, is brackish everywhere. 



The water (lowing under the compact alluvial cover from the 

 higher environs of the Haarlemmermeer polder has there, as I showed 

 in my former communication, a tendency to rise and so the salt- 

 retaming proi)erty of the fen can here act in an op^iosite direction 

 as in the shallower polders in w liicli the vertu'al component of the 

 water is directed downward. 



i.\s the old fen forms, as it were, a filter for sodium chloride, 

 so in the shallower polders the "old sea-clay" by its high percentage 

 of iron, keeps the water in the underground relatively free from 

 sulphuric acid. The superficial fen in the Ivieker |)older contains so 

 much compounds of sulj)hur that it has a very strong smell of 

 sulphuretted hydrogen, when freshly dug. Water squeezed out from 

 it proved on analysis by Dr. Schookl to contain no less than 408 mg. 



