Water Supply. 283 



nomical use, and the means which Avill afford increased facilities 

 in obtaining them, is the chief object of this communication. 



The water-bearinof formations above the chalk are g-enerally of 

 so superficial a character, and so complicated in their g-eolog-ical 

 structure, that no definite rule can be laid down as to the water 

 they contain. The elaborate Reports published by the General 

 Board ot Health on the proposed supply of water to London from 

 the Bagshot sands in 1850, are a sufficient guide to those who 

 wish to investigate that question. Though these sands in some 

 localities are of considerable thickness, and from the alternation 

 of the sands with clay beds throw out water at various levels, 

 they very often represent sources of land-springs. 



The chalk formation occupies a large surface of the east and 

 .south of England, and may be said (if we include the tertiary- 

 beds by which it is partially covered) to extend from the Chiltern 

 range to the German Ocean. This is the chief source of the 

 water supplied to the Thames and many other rivers. The water 

 falling on its surface where exposed, or where covered with 

 pervious beds of gravel, sinks into this stratum and forms a sub- 

 terranean bed of water, the surface of which has been called the 

 chalk-water level. The depth at which water may be reached 

 in the chalk may be made a matter of calculation. Take the 

 level of any known spring or outfall, and then allow for an incli- 

 nation of 10 feet per mile at least as the inclination of the water- 

 line, it will be found that the surface-line of the subterranean 

 water dips towards its nearest vent, the angle of inclination being 

 ruled by the friction or resistance encountered by the water in its 

 passage through the stratum. As the subterranean supply is 

 replenished, this line will rise at an angle increasing with its 

 distance from the vent. 



A section, C (see next page), based upon absolute measurement 

 and frequent observation, through a long period, is given to illus- 

 trate this phenomenon. If the level of water in two wells situate 

 in a line to the outfall be ascertained, the water will be reached in 

 a well to be made midway between them at the mean depth of the 

 two ; and this will be true of all wells sunk in any water-bearing 

 stratum at all like the chalk. The raising of water from the 

 chalk in the upper levels, where the water-level lies 300 or more 

 feet below the surface, must be laborious and expensive. An 

 Indian magnate, the Maha Rajah of Benares, intrusted to my 

 friend, Mr. E. A. Reade, C.B., a sum of money to be employed 

 for the benefit of the poor, on an object not of a religious cha- 

 racter. He expended it on a well in the chalk, 358 feet deep, 

 furnished with simple but most serviceable machinery for raisino- 

 the water — large buckets, chains passing over iron sheaves, 

 wound up by a winch and flywheel. Contrivances, such as a 



