r three
hundred years to reach a point in the southern part of the state where
they are tapped. Because of this slow movement, a large number of wells
in any one spot may exhaust the local supply faster than it is
replenished from the remainder of the formation. The drilling of
additional wells near at hand in such cases does not increase the total
yield, but merely divides it among a larger number of wells.

The porosity of the rocks, and therefore the flow of an artesian
circulation, may in some cases be artificially increased by blasting and
shattering.

COMPOSITION OF UNDERGROUND WATERS

Underground waters are never entirely free from dissolved mineral
substances, and seldom are they free from suspended particles. Some
waters are desired because they contain very small quantities of
dissolved mineral matter. Others are prized because they have an
unusually high content of certain mineral substances. In determining the
deleterious or beneficial effect of dissolved substances, much depends
on the purpose for which the water is to be used,--whether for drinking,
washing, steam boilers, or irrigation. Near the surface underground
waters may carry bacteria, as well as animal and vegetable refuse,
which from a sanitary standpoint are usually objectionable. Deeper
waters are more likely to lack this contamination because of filtration
through rocks and soils.

The dissolved mineral substances of underground water are derived for
the most part from the solution of rocks with which the waters come in
contact, particularly at or near the surface. Through the agency of
underground water most of the mineral and chemical changes of rocks are
produced. The dissolved substances in solution at any time and place may
therefore be regarded as by-products of rock alterations. Locally they
may to some extent be derived from direct emanations from cooling
igneous masses.

The most common mineral substances contained in waters are lime and
magnesia. Less common, but abundant locally, are soda, potash, iron, and
silica. Waters contain also certain acid and gaseous substances, the
most common of which is carbon dioxide; and less widespread, but locally
abundant, are chlorine and sulphur dioxide. Where lime and magnesia are
abundant the water is ordinarily classed as a hard water. Where absent,
or subordinate to soda and potash, the water is ordinarily classed as a
soft water. Large amounts of the acid substances like chlorine and