280 Water Supply. 



is the case at Tottenham, Tooting-, Uxbridge, and other places. 

 The depth to which the borings must be carried varies con- 

 siderably. The subterranean geology of London and its immediate 

 environs, as an example of the condition of the London basin 

 extending from Essex to Hampshire, will be best understood by 

 plans and sections published by Mr. R. W. Mylne, C.E. 



Water will rise in artesian or artesiod wells throughout the 

 London basin, where the chalk is covered by the London or 

 plastic clays. Though ruled by various outfalls, and disturbed 

 in some cases by faults, the height it will attain may be made a 

 matter of calculation : the great difficulty is the thickness of the 

 upper strata, especially where the surface of the clays rises in hills 

 and ridges, or where they are covered by the Bagshot sands. If, 

 by way of example, a line from Basingstoke to Colchester be 

 taken, where at the former place the water in the chalk stands 

 240 feet above Trinity high-water mark ; at Strathfieldsaye, 

 G^ miles distant, in a well sunk by the late Duke of Wellington 

 for the use of the villagers, 300 feet down to the chalk, the water 

 rises to within 15 or 20 feet of the surface, which may be 150 feet 

 above Trinity high-water mark ; at Boar Wood 350 feet to the 

 chalk, the water stands about 120 feet above Trinity high-water 

 mark ; at Cricklewood, where this line intersects that of the section 

 given, the water is 60 feet above Trinity high-water mark and 

 270 feet to the chalk ; at Tottenham 70 feet above Trinity high- 

 water mark, and 140 to the chalk ; at Witham (the outlay here 

 was 150/.), 306 feet to the chalk, water within a few feet of the 

 surface, about 120 feet above Trinity high-water mark ; at Col- 

 chester, 143 feet to the chalk, water about 5 feet above high- 

 Avater mark. 



In the Hampshire basin, though geologically the same as that 

 of London, the condition of the chalk, probably from greater dis- 

 turbance, cannot be relied on as a source of supply for artesian 

 wells. A well dug on Southampton Common to a great depth 

 was a gigantic failure. Again, at Portsmouth Dockyard the chalk 

 was reached at 400 feet, and pierced an additional 500 feet without 

 success. But here considerable quantities of water are obtained 

 for the supply of the Dockyard by boring into the beds overlying 

 the tertiaries, a district too small to come within the scope of our 

 subject as connected with the interests of agriculture. 



Following our inquiry into the supplies to be procured by 

 boring, according to the geological series, the next in order is the 

 gault clay, which occupies a rather narrow slip of country, more 

 or less, from Dorsetshire to the Wash. It is also developed in 

 the Isle of Wight, under the Sussex Downs, and in Yorkshire. 

 The artesian wells at Cambridge, sunk through the gault into 

 the lower greensand, are a notable instance of success. The 



