ON THE SUPPI^Y OF WATER TO TOWNS. 69 



a cubic foot per second for every 1000 acres of contributing area, as in the 

 Washbourne, one of the tributaries of the river Wharfe in Yoriishire, to f of 

 a cubic foot per second from the same area, as in tlie river Etherow at the 

 Manchester Water- Works. The spring-water of the Rivington Hills, from 

 whence the supply of Liverpool is to be obtained, is equal in the same dry 

 season to about half the quantity of that yielded by the Manchester district 

 in proportion to their respective areas. The general lowest yield of these 

 measures in the dryest weather, after a long period of drought, is about ^ 

 or I of a cubic foot per 1000 acres. These are the quantities measured in 

 the streams, the produce of considerable tracts of land, and are liable to be 

 increased and discoloured by floods. There are seldom any large or import- 

 ant individual springs. The Manyvvells Spring, near Bradford in Yorkshire, 

 is one of the largest. When at its lowest, except in extreme drought, it is 

 about 200,000 gallons a-day, but will average about 300,000. 



The abundance of spring-water found in the limestone which lies below 

 the millstone grit has been alluded to. Of that which issues from the old 

 red sandstone I have no certain information, but it probably closely resembles 

 in quantity that yielded by the lower coal-measures and the millstone grit. 



Beneath these, in geological series, the rocks generally become so compact 

 and so little fissured as to allow the infiltration of a very small portion of the 

 water which falls upon them, and the springs are consequently insignificant, not- 

 withstanding the abundant quantity of rain which prevails in the mountainous 

 districts peculiar to these formations. Measurements in the mica-slate in 

 Scotland in the summer of 1853, give results smaller than those obtained in 

 the millstone grit, notwithstanding the greater elevation of the ground and 

 the much larger annual rain-fall. 



2. From Artesian Wells. — The obtaining of water by means of wells 

 sunk into absorbent measures, "water-bearing strata" as they have been 

 called, overlaid by other measures of a retentive or impervious character, or 

 by wells sunk into permeable rocks like the new red sandstone, is a system 

 which has been widely adopted, and with considerable success. Such is the 

 mode by which both Paris and London are to a great extent supplied, as well 

 as Liverpool, Birkenhead, W^olverhampton and other places in this country, 

 and Tours, Calais, Venice and other places on the continent. 



Where absorbent measures are covered by others of an impervious cha- 

 racter, as the greensands and chalk are in the London basin by the plastic 

 clay, and where the absorbent or water-bearing measures are supplied with 

 the water they contain from elevated districts where they rise to the surface, 

 and where they receive and absorb the rain, the manner in which the water 

 is obtained is the most simple and convenient. A bore-hole of suitable size 

 is sunk through the impervious overlying stratum or strata to the measures 

 beneath, which are charged with water received from their distant elevated 

 outcrops. As soon as the water-bearing measure is reached, the water pent 

 down by the overlying impervious mass is released, and rises through the 

 bore-hole to the surface of the ground, where, if the supply be abundant and 

 the pressure great, it will overflow in a constant stream. 



The name of Artesian Well is said to have been derived from wells of this 

 description having been first constructed in Artois, in the north of France, 

 where the geological structure of the country favoured their easy and econo- 

 mical construction. In France, large quantities of water are obtained in 

 this manner. At and near Tours fifteen wells yield about ^.OOOjOOO gallons 

 per day ; one well alone supplying as much as 950,000 gallons in twenty- 

 four hours. The well at Grenelle, in Paris, yields 880,000 gallons of water 



