501 
CHAPTER XVII. 
SPRINGS AND WATER SUPPLY. 
THE Oolitic limestones, by reason of their porous and jointed 
character, constitute important water-bearing strata ; and the 
same may be said of the principal sandy strata. The water 
mostly is hard ; but this hardness is of the " temporary kind," 
due to carbonate of lime. The water in the deeper wells is as a 
rule excellent for drinking-purposes : that in the shallow wells 
is often liable to pollution.* 
Along the outcrop of these strata, springs of a more or less 
copious character mark their junction with underlying clays ; and 
the presence of these springs and of the porous strata that readily 
furnished a supply of water from shallow wells, determined the 
positions of the majority of villages and towns. Nevertheless in 
many instances in the area to the north-east of Aylesbury, 
Bicester, and Banbury, the coverings of Drift clay and gravel 
have modified the sources of Water from shallow wells. 
In considering the water-bearing character of the Lower 
Oolites, it must be borne in mind that each great division varies 
in thickness and in lithological character, so that the yield of 
water in one locality, apart from other circumstances, is no guide 
to the water-bearing qualities of the same formation at a distance. 
Such remarks apply especially to the Great Oolite, when we 
compare the mass of limestones that occur near Bath and onwards 
to Minchinhampton and Tetbury, with the series of limestones, 
in which so many layers of marl become intercalated, in the 
Eastern Cotteswolds, in Oxfordshire, and in the country to the 
north-east. 
Owing to the general eastsrly dip of the strata u good deal of 
the rain-water that falls on the escarpments flows away under- 
ground through the porous strata along the dip-slopes; while 
other portions escape here and there in the form of springs along 
the slopes of the escarpment, and thus enter distinct areas of 
drainage. This is the case with the "cliff" of Lincolnshire (see 
Fig. 60, p. 215), and with the Cotteswolds ; although in the 
latter district the numerous faults, certain undulations in the 
strata, and the deep ramifying valleys, modify to some extent 
the ultimate direction of the waters and the outflow of springs. 
Disappearance of streams Swallet-hoks. 
Springs or streams traversing the outcrop of successive strata> 
sometimes lose much in bulk when passing over porous rocks : 
* See Sixth Report of the Rivers Pollution Commission, Domestic Water Supply, 
1874, pp. 23, 81,97, 120. 
