146 
J. HOPKINSON-WATER AND WATER-SUPPLY 
water causes the plane of saturation to assume an inclination of from 
24 feet to the mile at the higher ground to 12 feet to the mile at 
the lower, where the water issues out in springs, on the surface of 
the ground, in pools, or in the beds of our rivers. The greater the 
rainfall, the steeper will be the inclination of this plane ; the greater 
the amount of water abstracted by pumping from considerable 
depths, the steeper it will be ; but in the former case it will be 
raised towards the surface of the higher ground, as it is in winter 
by the water percolating into it faster than it can flow through it 
laterally to the rivers and springs, and in the latter it will be 
lowered towards the point of abstraction. 
In this, as in all Chalk districts, the rivers are supplied by 
springs issuing out of the chalk where the inclination of the 
plane of saturation is greater than the inclination of the surface 
of the ground, when this is caused by an excess of water; and 
the rivers on the Chalk, if no impermeable strata intervene, only 
flow over the surface when their beds cut into this plane, for if it 
were below their beds the water would sink into the chalk and 
disappear. 
Hear the sea the natural outlet for the surplus water in the chalk 
is undoubtedly along the cliffs and under the bed of the sea itself; 
but inland, as here, the natural outlet is in the springs which 
supply the rivers. These are not only at the sources of the rivers, 
but they are also of frequent occurrence along their beds, the flow 
of the rivers thus being constantly augmented without the aid of 
any tributary streamlets. These springs are due to the overflow of 
the subterranean reservoir, and they are therefore an absolute 
measure of the amount of rain which percolates into this reservoir, 
when there is no leakage and its resources are not artificially drawn 
upon. When, therefore, there is an artificial abstraction of water, 
as from wells, there must be a smaller supply for the rivers to the 
extent of that abstraction. 
When the Colne Valley Water Company was projected, it was 
stated that the well would be steined or made water-tight for 
a sufficient distance downwards from the surface of the ground to 
ensure that no water would be abstracted from the Colne. Let us 
see how far this precaution is of any avail. Suppose that any of us 
had an underground tank supplied by the rain falling on the roof of 
our house, with an outlet near the top, from which, when the tank 
was nearly full, a stream of water flowed through our garden, 
keeping our ferns and rock-plants fresh and green throughout the 
summer, except in very dry seasons, and our neighbour said that he 
should like some of the water for his own garden, and if we would 
let him take as much as he wanted, he would take it without de¬ 
priving our garden of any, for he would merely put a pump into 
our tank and take care that uo water came into the pump except 
from the bottom of the tank, should we let him do it ? We should, 
I think, rather say : “Ho, you may take as much water as you 
like from the stream which flows through our garden, after it has 
passed our rock-work, but you shall not pump it from our tank.” 
