FROM THE CHALK OF HERTFORDSHIRE. 
159 
"But we can never even be certain of the absence of fissures or 
channels through which water may freely flow. In our sewage- 
farms and cemeteries the ground is so frequently disturbed that such 
fissures may not show on the surface as swallow-holes, as they would 
do in course of time on undisturbed ground. There is far less 
likelihood of contamination from these sources in our rivers than 
there is in the chalk, for water is usually, and may be nearly 
always, taken from rivers above such sources of pollution, while 
borings are most frequently made in thickly populated localities, 
and almost necessarily where the ground is low. 
But our rivers cannot be further drawn upon, and it seems there¬ 
fore that London must, sooner or later, follow the example of other 
and much less wealthy towns, by obtaining a supplementary supply 
from a distant source. Liverpool now obtains its water from the 
Yyrnwy, Manchester from Thirlemere, and Glasgow from Loch 
Katrine, while there is a project on foot for Birmingham to obtain 
a supply from Central Wales. If London delays, the most accessible 
sources of supply may be taken up by our Midland towns. 
The most feasible scheme appears to me to be to obtain a supple¬ 
mentary supply from Bala Lake, or some other lake or lakes in 
North Wales; or from Central Wales or Dartmoor. 
The rainfall, in England, decreases from the west to the east; 
even in our own county the difference is apparent, the Colne river- 
basin on the west having a greater rainfall than has the Lea 
river-basin on the east. In North Wales, in the vicinity of Bala 
Lake, the rainfall is twice as great as it is in the neighbourhood of 
London. We can rely there upon an average annual rainfall of at 
least 50 inches ; allowing 20 inches for evaporation and absorption 
by vegetation, there will be 30 inches available. This is five times 
as much, for every square mile of surface, as we can count upon in 
the London basin, and there is a collecting area which would at 
least suffice to supply the requirements of the increasing population 
of London for domestic purposes for many centuries. 
More than twenty-five years ago Professor Ansted thus referred 
to the project to convey water from Bala Lake :—“ Where there is 
a natural lake of pure water sufficiently large and well supplied to 
ensure a permanent supply, no better source can exist. Thus it 
has been proposed to convey the water of Bala Lake, in North 
Wales, to supply London with water ; and the idea, though it has 
not been carried out, was by no means so extravagant as might at 
first be supposed. The enormous cost of conveyance is, of course, 
a great barrier against the adoption of any such plan, but the 
possession of a vast natural reservoir, always full of the purest 
water, is no slight matter.”*' Against this proposal the objection 
has been raised that the substitution of a soft-water for a hard-water 
supply might lead to lead-poisoning. No instance of such poisoning 
with a soft-water supply is, I believe, known, but the possibility 
of it may be prevented in two ways : (1) by still deriving a portion 
of our supply from chalk wells or from our rivers, the water in 
* ‘ Applications of Geology,’ pp. 85, 86. 
