THE PRESIDENTIAL ADDRESS.
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showing that the original level of the subterranean streams is not
widely different; but the character of the water varies much within
comparatively small distances, thus showing that the channels run a
long way without mixing.
In wells near the Thames it is sometimes found that if pumped
too fast they give brackish water, thus showing that they are near
the outlet of the channel.
Without entering into so burning a question as that of the water
supply of London, I may venture to express a doubt whether Wales,
or even Westmoreland or Cumberland, affords a safer gathering
ground for water than the Lea Valley. For full utilisation of the
supply there are various problems to be considered, and not the
least of them is how much water can be drawn from the Chalk itself
and how far the level of wells and streams in the Upper Chalk is
affected by pumping from artesian wells in the Lower Chalk. On
these points there is great difference of opinion, and the question
can only be answered by careful observations of what is happening
during a particular period, and by comparison of all the records
obtainable of the effect of drought and flood upon wells in
various situations. We need all the information obtainable to
trace the course of subterranean streams and to form a complete
idea of the relation of the volume of the streams above and below
ground.
So far as I know, the evidence is that a period of about six
months elapses between the occurrence of a wet season and any
perceptible rise in the level of water in an artesian boring, when
the water is allowed to rest till the level is constant.
One side of this question is how far a drainage of the Upper
Chalk, brought about by pumping from artesian wells, is followed by
a diminution of the liability to flood, and how far the Chalk can be
utilised as a reservoir against dry seasons. If the surplus water
could be stored in the Chalk itself, instead of exercising the ingenuity
of engineers to get rid of it as an evil, it might be possible to find
a reservoir vast enough to foil even the machinations of the London
County Council.
It is interesting to look back to the first recognition of the value
of the water supply of the Lea Valley, in the great work of Sir
Hugh Myddelton. As not unfrequently happens, the insight and
foresight of a great genius not only provided a source of supply
fulfilling all the requirements of the severest judges of his own day,