206 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
thirty years an average of 500,000 gallons per day has been 
pumped, this would give a total of over 17,456 tons of solid 
matter removed. The rock-bed has a specific gravity varying 
from 2-5 to 2*8, say 2-7 on the average, then 17,456 tons of 
it would occupy a space of nearly 282,000 cubic feet, and 
the matter actually dissolved probably more than this 
amount, because of a lower average specific gravity. After 
making large allowances for solid matter derived from super¬ 
ficial sources—soil or gravel—and possible shrinkage of the 
bed, it must be evident that it is made more porous by use. 
Wells do often improve considerably with use. 
It may be demonstrated that water flows from one point 
to another in a saturated porous bed with a head due to the 
difference of vertical level of area of outcrop to that of area 
of discharge, less the frictional resistance ; also that increase 
in the carrying power of a bed is almost in direct proportion 
to the water pressure.* 
Through the kindness of Sir George Bannerman, Bart., 
I am able to offer some direct evidence of the porosity of the 
Maidstone in the neighbourhood of Brackley. Brackley 
Town Well was commenced in 1874 under the advice of my 
late friend Mr. S. Sharp, F.G.S., F.S.A., and reached a 
depth of 177 feet 6 inches.! The water then rested at 
100 feet from the surface ; that is, there was a head of water 
of 77 feet 6 inches. In 1882 this head was reduced to 
41 feet; May, 1884, to 89 feet 6 inches; September 17tli, 
1884, to 36 feet 6 inches. When this last depth was taken 
the pump had been stopped from Saturday at noon to 
Monday afternoon, so that the natural water level might be 
ascertained. The pump used at Brackley discharges 6,000 
gallons per hour, and after six hours’ continuous pumping, on 
September 17tli, the water level was reduced 11 feet 6 inches, 
leaving 25 feet in the well, and below this the pump could 
not bring it. In a few hours after the pumping was stopped, 
the water stood at the same level as before it was commenced, 
rising 2 feet in the first fifteen minutes. Here an increase of 
the difference between the water level inside the well and in 
the bed, of 111 feet, produced a flow of water of 6,000 
gallons per hour, or 144,000 gallons per day. A simple 
* Mr. De Ranee quotes some experiments made with New Red 
Sandstone blocks, which gave the following results :—With a pressure 
of lOlbs. to the square inch, 4J gallons of water passed; with 201bs., 
7£ gallons ; and with 461bs., 19 gallons. 
f I may say that the depth of well and height of water at first 
were originally given to me by Mr. Sharp, and differ a little from 
those afterwards given me by Sir Geo. Bannerman, and quoted above. 
