460 UNDERGROUND WATER SUPPLY 
where it is hopeless to expect a fair supply of potable water at moderate 
depths. 
I suggest that what is urgently needed is that regions with well-defined 
physiographical, formational or tectonic limits should be selected for hydro- 
logical study. For water supply purposes it has generally been the custom to 
choose county boundaries as the defined limits, as in the case of the Water 
Supply Memoirs of the Geological Survey. For administrative purposes there 
is good reason for adopting these county boundaries, especially now that 
the county councils have some control in financing and administering 
rural areas in the matter of water supply. But for the purposes we are now 
considering it is preferable to adopt natural unit areas, such as a river 
basin or watershed, or a tectonic structure like the Hampshire Basin, or 
a formation unit like the Chalk or the Bunter, or, perhaps better still, a 
specific water-bearing formation in some watershed or unit geological 
structure. 
The quantities of underground water which are pumped for long and short 
periods in the whole areas so defined should be estimated, and the rainfall 
statistics of the region recorded for the same periods, together with the 
surface conditions, including topography, cultural features, built-up areas, 
and so forth. In addition to quantities of water pumped at individual 
stations, we want details of static and pumping levels, and the effect of 
pumping at any one station upon neighbouring wells, streams, etc. 
In such a defined region continuous records of water levels in wells should 
be kept, and if possible springs and streams gauged systematically. During 
the progress of such work it would be possible to express graphically the 
hydrological conditions. But I would stress the necessity in all such 
correlations of taking practically simultaneous records—for example, of the 
water-table. When we realise that the well levels in the Chalk country, 
for instance, may vary seasonally as much as 150 ft. or even more, we can 
understand the necessity of correlating data and expressing the facts as they 
are at a given time. 
I am well aware that useful work of this nature has already been done in 
a few isolated areas, and I gratefully pay tribute to such valuable contribu- 
tions as those of Mr. D. Halton Thomson on the hydrological conditions 
of the Chalk of West Sussex, and the more general hydro-geology of the 
Chalk of England by Mr. R. C. S. Walters, and others. Their work should 
be an incentive to geologists interested in this branch of our science. I am 
convinced that the systematic collection and correlation of hydro-geological 
data at present available, together with new ascertainable data, would 
prove of the greatest value, both as a contribution to pure science and for 
the full and proper utilisation of our water resources. Work of this nature 
could best be done by geologists with an intimate knowledge of the areas 
selected for study. 
In the past many records have been published which are more than 
imperfect and faulty—they are positively misleading. It is not to be ex- 
pected that a boring foreman or well-sinker should correctly name the strata 
passed through ; it is not always insisted that cores are properly laid out 
and marked ; water levels are stated without surety that they are true rest 
levels, and quantities given as pumped may be the initial yield, and not the 
constant yield after equilibrium has been established. 
The composition of underground water is a subject of sufficient importance 
to warrant separate treatment. Apart from organic purity, which is essential 
in all potable water supplies, there are limits of mineral content beyond 
which water is unfit for general domestic or industrial use. I know of little 
work so far done in preparing graphs and charts showing the geographical 
