( 752) 



that region '). E\'er since, a few years ago, the level of the H. M. 

 pokier was lowered 0.30 M., the le\'el of the water in a pond, 4 M. 

 higher, al Meer-en-Berg, and 400 M. outside the ])older, was observed 

 to be lowered as much. From this we can imagine how powerful 

 the influence of a lower level of 5 M. nnist have been at the 

 time Avhen the Lake of Harlem was being drained dry. 



As to the motion of the deep underground water, at the side of 

 the dunes, facing the sea, 1 have been able to make only a few 

 observations. The great uniformity Avith which the dunes border on 

 the sea however, in connection with the other results of my investiga- 

 tion, permit drawing pretty safe conclusions from them, as to the 

 general condition. 



A well known fact is that the superticial water Hows from the 

 dunes towards the sea, just as it does inland from the dunes to 

 the adjacent tlat area and the polders. A remarkable proof of the 

 water flowing from the dunes to the sea, is the welling up, at 

 ebb-tide, of fresh water on the beacli, north of Noordwijk-aan- 

 Zee. Puddles and furrows form themselves, from which, as long 

 as it is ebb, not unHke rills, fed from sources, large quantities 

 of water, only partly consisting of salt-water, flow towards the sea. 

 Particles of clay brought up with the water and found in the ripple- 

 marks on tlie beach, suggest the presence of a clay-bed, close to 

 the surface, through interruptions of which the welling u}> of the 

 water takes place. On March 27'i' 1903, at 1Ï a.m., it being low- 

 tide, about 9 hours after high-tide, (the wind S.S.E.), I scooped 

 opposite stmnd-pole N". 78, from such a rill, about 200 M. long, 

 (the debit of which miglit be calculated to be in the least 7 M' an 

 hour), a sample of water, which proved to contain 11550 niG. of 

 chlorine the Liter. So for \/^ it was fresh- and for -/j sea-water, 

 and hourly more than 2.3 M' fresh water found its way into the 

 sea, through that little ebb-rill. The great uniformity now with which 

 the dunes slope dowji to become beach permit us to accept as 

 a general though in most cases invisible fact what here, through 

 local circumstances, ha[)i)ens visit )ly. 



Another proof for the considerable flowing down of fresh surface- 

 water towards the sea, furjiished to me a stone- well at the foot of the 

 dunes, on the beach at Zandxoort, from which the fishing-smacks 

 take their water-store. The bottom of that well is 0.72 M. ~ A. P., 



1) That also from the euciicliiig canal itself, which is about 3 M. ^ k.P. deep, 

 the water is sinking down, is proved by the fact, that near the Gruquius, tlie 

 level is always some centimeters lower than in the Spaarne and in the canals 

 of Harlem. 



