PROM THE CHALK OF HERTFORDSHIRE. 
1-17 
The two cases are similar.* The Colne Valley Water Company was 
allowed to erect a pumping-station, put one or more pumps into the 
reservoir in the Chalk from the overflow of which the Rivers Colne 
and Ver derive their supply of water, and to pump any amount of 
water from the bottom, or near the bottom of this reservoir, on the 
simple assurance that no water should be taken from the top, or 
near the top of it. This is not a single case, the farce has been 
enacted over and over again, but I think that the knowledge of the 
underground circulation of water has spread to such an extent that 
very few would now say to their neighbour : “ You may draw as 
much water from the bottom of my tank as you like, if you will 
let me have all that overflows from the top.” 
It has been argued that there is a leakage from our underground 
reservoir—that some of the water flows under London and into the 
sea—and that by pumping we are reducing this amount; but, again 
to borrow our homely illustration, should we be any more inclined 
to let our neighbour pump the water out of our tank if we knew 
that there was a leakage, and that, when the tank was full, the over¬ 
flow did not represent quite all the water which flowed into it? 
With regard, however, to this possible leakage, it should be 
borne in mind that the main question of the availability of under¬ 
ground water for a water-supply—whether from our surface-springs 
or deep wells—is one of time. The natural leakage under London 
must be slow, for it is well known that the Chalk, under the great 
mass of Tertiary strata, is much more compact than it is on its out¬ 
crop, and therefore must offer here a much greater resistance to the 
passage of water through it. This is due, partly to the pressure of 
the London Clay and Lower Tertiaries, and partly to the fact that 
the chalk under these impervious beds is not subject to dissolution 
by the percolation of water from the surface. In our chalk-pits 
we never see “ pipes,” which are thus caused, when there is a thick 
bed of clay over the chalk. The leakage would be increased by 
water being pumped from great depths under London itself, and 
doubtless by this means channels have been formed in the Chalk 
under the London Clay. If water be continuously withdrawn from 
our underground store by these channels more rapidly than it is 
supplied by percolation, the water-level must be lowered, and the 
overflow which feeds our rivers must be lessened, and in course of 
time cease altogether in dry seasons. Although the natural leakage 
must be so slow that it cannot prejudicially affect the flow of our 
streams, it is very different when water is artificially abstracted 
from the lower part of our valleys by exhaustive pumping, and is 
conveyed quite away from their drainage-area, or when channels 
are formed by pumping at a distance, as in London. By such 
* A filter, however, affords a more precise parallel to our reservoir of saturated 
chalk, but the only difference between it and a tank which affects the argument is 
one of time. No one would contend that water could be drawn from the bottom of a 
filter without the amount of water in it being reduced, and the surface consequently 
lowered, although some time would be taken by the water to filter through. A 
similar illustration—that of a tank—has been used by Sir John Hawkshaw and 
Dr. John Evans. See ‘Proc. Inst. Civ. Eng.,’ vol. cv. (1891), pp. 57 and 62. 
