G. Lou-ker — Water-supply of East Kent. 207 



Hardres Eectory, writes, " This well was formerly 300 feet deep, but 

 failed in the dry seasons of '56 and '58, when it was deepened 

 60 feet. The water-level lowers in autumn from 20 to 30 feet." 



The Chalk area is by far the largest in this district, and, exclusive 

 of the Isle of Thanet, equals about 296 square miles. While the 

 area of the Tertiary beds is about 158 square miles. 



The rainfall of the district is subject to considerable variation, and 

 more statistics on this head are needed. At Sheldwich the average 

 rainfall for three years 1883 to 1885 equalled 25-99 in. At Canter- 

 bury for ISSi it was equal to 20-83 in. At Eamsgate for three years 

 from 1883 to 1885 = 21-81 in. While at Horton Park I have for 

 1883 above 30-00 in. It must be remembered that the last three 

 yeans were exceptionally dry ones. 



One inch of rainfall represents about 100 tons of water to the 

 acre. A portion of this is lost by evaporation, and some passes away 

 underground to sea ; the remaining portion constitutes our available 

 supply in rivers and wells. 



A consideration as to the permeability of different beds, and their 

 capacity for retaining water, will form an important element in our 

 calculation. We may consider the Chalk area as the most important, 

 not only as the chief water reservoir, but as constituting by far the 

 largest portion of the district, and it will be found that it is through- 

 out its extent extremely permeable when not saturated with water, 

 down to a short distance from the Gault. The large supplies of 

 water required for the Canterbury Waterworks, the Chartham 

 Asylum, the Canterbury' Breweries, the wells for drinking water at 

 Eamsgate, Margate, and Dover, are all derived from this formation. 

 In the case of the deep boring for the Convict Prison at Dover, made 

 during this year, when strata were pierced to the depth of over 900 

 feet (penetrating both Gault and Lower Greensand), the water- 

 supply was chiefly, if not entirely, derived from the upper three 

 hundred feet, all in the Chalk. The time taken by the water to 

 reach the line of saturation in this Chalk area appears to be about 

 three or four months, and the height of the springs varies in propor- 

 tion to the rainfall. 



The Chalk area is in some places capped by impermeable beds of 

 clay, as at Swingfield Minnis, but the clays and gravels over the 

 Chalk are for the most part permeable. North of Canterburj^ over 

 the Tertiary area, the permeable beds are the sandy portions of the 

 Old Haven, Woolwich, and Thanet beds ; the lower parts of the 

 latter, however, are impermeable. Above these the London Clay 

 and the clay and gravel beds of the Blean district are impermeable. 



A narrow tract of land below the escarpment of the Chalk Downs, 

 stretching from Folkestone to Wye, is composed of impervious 

 Gault and pervious beds of the Lower Greensand. In many of the 

 wells, after piercing the Gault, the water flows up to, or over the 

 surface. In this area the water from the Sandgate beds of the Lower 

 Greensand is bad, being largely impregnated with iron. I have very 

 few data relating to the wells of this district, which is, however, 

 of little importance in the general survey of the water supply. 



