189 



to my knowledge, statements about it are few and far between. 

 Jkntzsch ') e.g. records that in the deeper ooze-layers of the ocean 

 of abont 40 m. and more, reduction-processes occur, in which hydro- 

 gen sulphid and ferric sulphid are formed, wliicii are ascribed by 

 him to decomposition of proteins. It is more likely, however, that 

 here also we have to do with sulphate-reduction, since it has been 

 proved that this is of frequent occurrence under the circumstances 

 alluded to. 



Another statement is given by Eug. Dubois *) who observed the 

 transformation of sulphate into ferric sulphid in the lower alluvial 

 clay-layers underneath the Dutch Dunes. 



An opportunity to ascertain the occurrence of sulphate reduction 

 in deeper layers was offered, when in the autumn of 1921 a number 

 of new wells were dug along the Sprenkelkanaal on the source of 

 supply of the Amsterdam Dune Waterworks. 



§ 2. How the samples of sand, clay and peat were obtained 

 from the well-shafts. 



In connection with the bacteriological sampling it will be well to 

 set forth, in principle, the way in which the new wells were sunk. 



A wide iron tube is dri\en vertically into a dug, shallow cavity. 

 The sand is excavated from a greater depth than is at first reached 

 by the tube, which can consequently sink gradually deeper. By 

 means of a screw-thread one length of tube is screwed on to the 

 other, so that a system of tubes is procured of the length necessary 

 to reach a certain depth. 



The masses of sand and the occasional lumps of clay and peat 

 are removed from the tubes with a so-called "puis", consisting of 

 a hollow iron cylinder of smaller diameter than the tube's. At the 

 lower end it is sharp-edged to facilitate the sinking, while the bottom 

 is provided with a valve, opening to the inside. By means of two 

 iron bars that are fastened to the edge of the open top-part of the 

 cylinder and are suspended on the same point of support, it is 

 possible to connect the apparatus to a pulley-block. When moving 

 the "puis" forcibly up and down in the wet mass of sand present 

 in the shaft, it is ultimately filled with a pap of sand. The filled 

 "puis" is then hoisted up and emptied by overturning it. This process 

 of removing the sand from the well-shaft is briefly called "pulsen". 



1) Zeitschrift d. Geol. Ges. 1902. 54, p. 144. Gf. Ramann, Bodenkunde, p. 180. 

 *) Het Leidsche Duinwater. Eene hydrologische studie. 1912, p. 19 eii 20. 



