( 74J ) 



is equal to that of sandy clay, hut that in aiiollier respect, it is 

 very ditFerent from clay, i.e. in its water-contaiiiiiifi' oapaeity. Wliereas 

 clay, like sand, can contain water for scarcely nioi-e Ihan a liiird 

 of the volume of the dry substance, non-compressed |wat can do so 

 many times over. Peat of the Rieker polder, near Sloten, on the 

 territory of the military \vater-works, A^as found to huxe a capacity 

 of holding water, nine^times the volume of the dry peat; and the 

 water in it can, altliough slowly, yet freely move. 



On the whole we have to deal with an upper-soil of finer, often 

 clayey sand water, and on which or in \vhich, in most j^laces, 

 enormous water-reservoirs occur: the peat beds, for e\en the com- 

 pressed peat contains still a large quantity of water. In the colder 

 (rainy) seasons the upper peat layers are not only always kept filled 

 with fresh water, but they can, though slowly, provide lo^ver regions 

 from their water-store ; and along with the water, no doubt with carbonic 

 acid, which deep below will dissolve iron and chalk ; and methane 

 which, in the same way as carbonic acid, the more easily dissolves, 

 the higher the pressure is. Deep down tiie latter product of decaying 

 organic matter, cannot be formed, on account of the absence of 

 bacteria. , 



Those upper-lay ei'S, little permeable, more or less shut off the 

 zone of gravelly coarse-grained sand which at the bottom, in a 

 similar way l)ut much more imperfectly, in ils turn is shut off by the 

 irregular beds of impure clay and fine-grained sand, occurring there. 

 Under those conditions the vertical motion of the water, must on 

 the whole be difficult; at one })lace more and at the other less, 

 according to clay or sand locally prevailing and in pro[)ortion to 

 the latter being finer- or coarser-grained, Avhereas in the coarse- 

 grained medium zone or zones, horizontal motion is comparatiA^ely 

 eas}' ; that medium zone is therefore the great channel, and in 

 extracting underground water this "water-vein" is generally found 

 at about 30 M. ^ A. P. or a little deeper still. 



That indeed below that depth the underground water has an easy 

 horizontal passage, appears from the fact, that the height to which 

 the water ascends in tube-w'ells, driven below the upper-edge of the 

 coarse-grained bed, falls but little; whereas higher up in the fine- 

 grained sand, it nearly always is considerably higher, (i.e. excepting 

 the deep polders, where the deep Avater \y\\\ nnturally rise above 

 the surface of the soil). 



As to fixing the direction in which the dee[) nnderground water 

 moves, a thing that will enable us to inquire after the existence of those 

 currents, supposed by some, and also the origin of the uiidergi-ound 



