WaterlSupply. 27? 



the wells in the village were more or less affected. If the supply 

 were less, and it was necessary for the sake of Tiptree farm 

 and establishment to economise the supply (and this may serve 

 as a general illustration), a well (call it of depression) on a large 

 scale might be sunk near the centre of the gravel-bed, whence 

 the greatest body of water might be raised by artificial means, or 

 allowed to pass by gravitation from the well to the lower levels 

 by some simple contrivance providing for the shutting off the 

 water at pleasure. Such sources of water, when practically 

 perennial, are often said to yield an undeviating volume ; a 

 periodical gauging would show that the quantity is in the ratio 

 of the natural exhaustion and replenishment by rainfall. 



It should be noted that sands and gravels are speedily re- 

 plenished ; as gravelly soils, from their silicious and stony character, 

 preclude such an absorption of water as takes place in loams, chalk, 

 and other substances after a period of drought. Careful observa- 

 tion and frequent measurements have shown that wells in sand 

 and gravel are replenished by a heavy summer shower ; whereas 

 it requires from 2 to 3 inches of continuous autumn rainfall to 

 replace the evaporation of the summer in the soils of a more 

 tenacious character. 



No general rules can be laid down for dealing economically 

 with sources or supplies of water held in drifts or gravels which 

 flow aboveground as landsprings, unless they are founded on the 

 ascertained geological condition, whether of the gravel-beds them- 

 selves or of the surface of the clay on which they rest. 



The gault, Kimmeridge, Oxford, lias, and other clays — which 

 are of the character of marls, as in the new red sandstone — pre- 

 sent, when their surface is exposed, a corrugated character. The 

 Keythorpe system of drainage is based on this fact ; if we may 

 judge by the present river action on the gault in the valley of 

 the Thames, this condition has probably a fluviatile origin. Be 

 that as it may, the cutting through one of these subterranean 

 stanks or ridges will often lay a large tract immediately dry. 

 This was the case in the city of Oxford, when a system of deep 

 sewer-drainage was attempted, by which the house-wells were 

 laid dry through a considerable district, till the stank of clay cut 

 through was restored by artificial means, when the water was 

 restored also. The section, A (see next page), made at the time, 

 is given as a good illustration. When, under such circumstances 

 the water-level has been affected, the wells have been sunk into 

 the subjacent clay ; but the water held in the clay is often so sur- 

 charged with mineral substances as to render it unfit for use. If 

 the water is not too much reduced in the drift, the bottom of the 

 well should be enlarged, as a sort of subterranean tank, rather 

 than pierce the clay under any circumstances. The surface, or 



