286 Water Supphj. 



out that the surface of the clay dipped in a certain direction, and 

 that the well should be sunk near the margin of the oolitic rock 

 in the direction of the dip. This was done, and water was 

 obtained in abundance. This principle sliould be kept in view 

 in seekinof a supply of water throughout the oolitic range and the 

 upper beds of the lias, where permeable beds rest on clay whose 

 surface dips in a known direction. The presence of water under 

 such circumstances is marked by the springs which issue from 

 the hill-sides at the junction of these beds. The lower oolitic 

 series, separated from the middle or coralline by the Oxford clay, 

 which overlies the lias, is one of the principal water-bearing 

 formations of England. 1/iko the chalk, its surface is furrowed 

 by frequent valleys, dtnvn which its waters find vent in perennial 

 streams ; though, unlike the chalk, its substance is interlaced 

 with bands of clay of varying thickness, which throw out the 

 water at every variety of level. These bands, besides the faults 

 caused bv disturbance, make it exceedingly difhcult to determine 

 the supply of water, and conse([uently the means which will afi'ord 

 the greatest facilities for obtaining it. It often happens that in 

 one locality there are several distinct beds of water, either to be 

 traced in wells, or to be seen, as indicated by springs issuing from 

 the hill-sides. Such, for instance, is the case at Stonesfield, in 

 Oxfordshire, where three distinct beds of water are found at 

 various levels, at about 15, 50, and 100 feet from the surface 

 respectively ; none, except the lowest, which rests on the lias clay, 

 vielding a large amount of water, but each sufficient for ordinary 

 domestic purposes. The only obvious way of increasing the 

 supply to the iipper wells is the enlargement of the lower chamber, 

 care being taken to avoid the hazard of sinking Ijelow the surface 

 of the clay at the bottom. Agricultural drainage often decreases 

 the subterranean supply to these strata ; yet water running from 

 the surface of the clays, which often cover large tracts, sometimes 

 sinks by natural swallow or swill v holes into the jiermeable rock 

 beneath, at the margin of the clay. These natural features might 

 be assisted by simple artificial means to the increase of the supply 

 to those strata. 



Many of the valleys of this formation rest on upper lias clay. 

 If, as in some cases, the base of the valley is the lower lias, the 

 intervening marlstone, usually charged with water, adds another 

 source of water to the district. Such valleys are well fitted for 

 the storage of water, such as in the reservoirs which supply the 

 summit-levels of the Oxford Canal, which have never yet failed. 

 From the marlstone, as from the partings of clay in the oolite 

 above, springs issue at so high a level above the foot of valleys, 

 as to enable farmsteads, other establishments, and villages, to be 

 supplied with water by gravitation, delivered through pipes or 



