alone on objective qualities
of composition, but rather on causes which lie in the fields of
psychology and commerce.

The part played by sentiment in putting value on water is well
illustrated by the general preference for spring waters as compared with
well waters. In the public mind, "spring water" denotes water of unusual
purity and of more desirable mineral content than well water.
Illustrations could be cited of districts in which the surface or spring
waters have a composition not different from that of the deeper well
waters, and are much more likely to be contaminated because of proximity
to the surface; and yet people will pay considerable sums for the spring
water in preference to the cheaply available well water.

RELATION OF GEOLOGY TO UNDERGROUND WATER SUPPLY

It is obvious that a knowledge of geology is helpful in locating an
underground water supply. Locally the facts may become so well known
empirically that the well driller is able to get satisfactory results
without using anything but the crudest geologic knowledge; but in
general, attention to geologic considerations tends to eliminate
failures in well drilling and to insure a more certain and satisfactory
water supply.

In drilling for water, it is essential to know the nature, succession,
and structure of the rocks beneath the surface in order to be able to
identify and correlate them from drill samples. The mere identification
of samples is often sufficient to determine whether a well has been
drilled far enough or too far to secure the maximum results. In order to
arrive at any advance approximation of results for a given locality, a
knowledge of the general geology of the entire region may be necessary.
Especially for expensive deep artesian wells it is necessary to work out
the geologic possibilities well in advance. It is useless, for instance,
to look for artesian water in a granite; but in an area of gently
inclined strata, with alternations of porous and impervious layers, the
expert may often figure with a considerable degree of certainty the
depth at which a given porous stratum will be found, and the pressure
under which the water will be in this particular stratum at a given
point. Even the mineral content of the water may in some cases be
predicted from geologic study.

One of the most obvious and immediately useful services of the geologist
in most localities is the collection and preservation of well samples
for purposes of i