198 



"From llie surface downwards in and underneatli the dnne-iiiasses 

 the sulphuric acid content diminishes proportionally to the total 

 thickness of the clay-Iajers occurring in them, i. e. in proportion 

 to the increase of the volume of clay-soil, through which the water 

 has percolated downwards. 



This phenomenon is the result of the power of clay-soil to convert 

 sulphuric acid and then retain it". 



In the study by Eug. Dubois^) already quoted above, a detailed 

 exposition is given of the transformation of sulphuric acid in the 

 clay-layers, which consists in a reduction-process in the presence 

 of organic matters, with formation of ferric sulphid. 



It is evident from the foregoincj that sulphate-reduction, which 

 occurs 7iot only in the deeper clay-layers, but also in the sand-soil, 

 is brought about by Microspira desulfuricans. The life of this microbe, 

 which IS adapted to anaerobic conditions, accounts for the common 

 occurrence of sulphate-reduction in the deeper layers of the earth and 

 especially in the clay-soil, which generally has a higher content of 

 organic matter. 



So long as the conditions of this typically } microbiological process 

 are fulfilled, transformation of sulphate into ferric sulphid ivill 

 hereby be generated, to ivhich is to be ascribed the paiHial or total 

 absence of sulphuric-acid salts in deep-dune rvater. 



Heemstede, February 24 1922. 



1) ,Het Leidsche Duinwater". Een hydrologische studie, 1912, p. 20. 



