( 740 ) 



one seventeenth. Tlie investij2:ations l»y Prof. Spring ^) have ])roved 

 the fact that, and the reason why. even verv Ihiek hivers of ini- 

 pnre clay, e. g. the Umon superinir df In Hrshuiic, let throngli water. 

 Wliat then mnst we think of our clay, wliicli. though technicians 

 will call it impermeable or '"rich clay", likewise, for the greater part, 

 consists of sand ! 



The chemical analysis of specimens of the fattest clay -sorts selected 

 from their outward look, (a large number of such specimens being 

 at my disposal from a variety (jf l»oiings) showed the real clay 

 percentage to consist of less than (( third: at Sloten (boring IV. 2, 

 at 4M.-: A.P.) and at Uitgeest (Station, at 43 M. ^- A.P.). Of about 

 (I fourtit: at Hoofddorp, Haarlenimei'meer (at 6 M. and also at 

 34 M. ~ A. P.) ; at Amsterdam (Dairy at the Prinsengracht, at 9 

 M. -^A.P.) and in the dunes, 3 K.M. west of Santpoort (at 40 M. rA.P ). 

 Of about <i llftli-- at Amsterdam, (Dairy in the Second Spaarndammer 

 Dwarsstraat, at 3.5 M. ^ A. P.); at Harlem (Hagestraat, at 14 M. ! A.P.); 

 at Hillegom (Treslong, at 14 M. -r A.P.) ; at Beverwijk (Middle of 

 Breestraat, at 19 M. ^A.P.); at Alkmaar (Station, at 22 M. r A.P); 

 in the northeni [tait of the Watergraafsmeer polder (near the Ooster- 

 railroad, at 35 M. -: A.P.): at Katwijk (875 M. South- West of the 

 water-tower of the Leyden waterworks, at 1.6 M. -!^ A.P.). Of about 

 a sLvth : at Sloten (boring HI. 1, at 5.50 M. -f A.P.) and at Eertden- 

 koning, in the west of the Haarlemmermeer polder (at 19.5 M. f A. P.). 

 Of about a .->eveiith: at Velsen (near Rosenstein, at 2.50 M. -r A.P.); at 

 Katwijk (in the same borings, Rt 'S.SM. -r A.F.). An eii/hth to a ninth: 

 at Beverwijk in the same borings at 5 M. -r A.P.) ; at Amsterdam 

 (Prinsengracht, at 6 M. '. A.P.) and in the Koningéduin near Castri- 

 cum (at 32 M. -r A.P.). Of less than a tenth: at Driebuis (Nunnery, 

 at 18 M. -f A. P.). Of about a ji/tecnth: at Amsterdam (Second 

 Spaarndammer Dwarsstraat, at 62 M — A.P.) ; at Hillegom (Treslong, 

 at 4 M. -r A. P.). Of about a seventeentli: in the Watergraafsmeei- polder 

 (at 8 M. r A. P.). No clay at all, at Amsterdam (Second Spaarndam- 

 mer Dwarsstraat, at 43 M. -.- A. P.). The last specimen, looking like 

 fine-sandy clay, proved to consist of sandy calcareous tufa with 

 777» CaCO,. ^ 



As to peat, experiments haxe >lio\\ u to me that its impenneableness 



1) W. Spring, Quelqacs experiences sur la perméabilité de I'argile. Annales de 

 la Société géologique de Belgique. Tome :28, p. 117— 127 (1901), and : Recherches 

 expérimentales sur la filtration el la penetration de I'eau dans le sable etlelimon. 

 Ibid. Tome 29, p. 17—48, 1892). Compare also the report of H. Rabozée on those 

 investigations in : ]>niletin de la Société beige de Geologie, de Paleontologie et 

 dllydrdogie. Tomo 16, p. 209-295, (1903). 



