WATER-BEAEIXG STRATA. 337 



The supply averages from sixteen to eighteen million 

 gallons per day to a population of from 650,000 to 700,000. 



At Birmingham the wells in the New Red Sandstone vary 

 from 130 feet to 400 feet in depth, supplying a population 

 of 450,000 to 500,000 from wells at Aston, Perry Well, 

 and King's Vale Wells, yielding 10,000,000 gallons per 

 day. 



At Wolverhampton the supply is from wells in the New 

 Hed Sandstone and from the river Worf, a tributary of the 

 Severn. 



At Nottingham the supply is from wells in the New Red 

 Sandstone at Basford and Bestwood, sunk to an average 

 depth of 190 feet, yielding three million gallons per day. 



Turning now to the West of England, the localities in this 

 stratification with which I am more familiar are those situ- 

 ated about nine miles to the west of Bristol, viz., at Chelvey, 

 near Yatton, and to the south-west in the valley of the Yeo, 

 twelve miles from the centre of this city. 



The rainfall in these districts averages from 31 to 42 inches 

 per annum ; of this, not less than from 14 to 16 inches 

 percolate into the sandstone. 



The chemical constituents of this sandstone are silica, 

 alumina, magnesia, lime, and iron. 



The sandstone takes up or absorbs about one-fifth of its 

 weight of water, or nearly one gallon per cube foot, especi- 

 ally if of an open nature. 



The quantity which will pass through a square foot ol 

 from 10 to 12 inches thick varies with the head. Thus at 

 23 feet, 4J gallons ; at 56 feet, 7J gallons ; at 105 feet, 19 

 gallons ; the increase being directly as the pressure. 



I should take in this district an annual percolation of 16 

 inches of rainfall, equal to 700,000 gallons per square mile, 

 as it is very heavily saturated, and the surface stands only 



