Water Supply: the Present Practice of Sinking and Boring Wells: With Geological Considerations and Examples of Wells ExecutedSpon, Ernest
Science
Water Supply: the Present Practice of Sinking and Boring Wells: With Geological Considerations and Examples of Wells Executed
Spon, Ernest
Boring; Water-supply; Wells
The next strata in which water is found are the upper and inferior
oolites, between which are the Kimmeridge and Oxford clays, which are
separated by the coral rag. There are instances in which the Oxford clay
is met with immediately below the Kimmeridge, rendering any attempt at
boring useless, because the water in the Oxford clay is generally so
impure as to be unfit for use. And with regard to finding water in the
oolitic limestone, it is impossible to determine with any amount of
precision the depth at which it may be reached, owing to the numerous
faults which occur in the formation. It will therefore be necessary to
employ the greatest care before proceeding with any borings. Lower down
in the order are the upper has, the marlstone, the lower has, and the
new red sandstone. In the marlstone, between the upper and lower beds of
the has, there may be found a large supply of water, but the level of
this is as a rule too low to rise to the surface through a boring. It
will be necessary to sink shafts in the ordinary way to reach it. In the
new red sandstone, also, to find the water, borings must be made to a
considerable depth, but when this formation exists a copious supply may
be confidently anticipated, and when found the water is of excellent
quality.
Every permeable stratum may yield water, and its ability to do this, and
the quantity it can yield, depend upon its position and extent. When
underlaid by an impervious stratum, it constitutes a reservoir of water
from which a supply may be drawn by means of a sinking or a bore-hole.
If the permeable stratum be also overlaid by an impervious stratum, the
water will be under pressure and will ascend the bore-hole to a height
that will depend on the height of the points of infiltration above the
bottom of the bore-hole. The quantity to be obtained in such a case as
we have already pointed out, will depend upon the extent of surface
possessed by the outcrop of the permeable stratum. In searching for
water under such conditions a careful examination of the geological
features of the district must be made. Frequently an extended view of
the surface of the district, such as may be obtained from an eminence,
and a consideration of the particular configuration of that surface,
will be sufficient to enable the practical eye to discover the various
routes which are followed by the subterranean water, and to predicate
with some degree of certainty that at a given point water will be found
in abundance, or that no water at all exists at that point. To do this,
it is sufficient to note the dip and the surfaces of the strata which
are exposed to the rains. When these strata are nearly horizontal, water
can penetrate them only through their fissures or pores; when, on the
contrary, they lie at right-angles, they absorb the larger portion of
the water that falls upon their outcrop. When such strata are
intercepted by valleys, numerous springs will exist. But if, instead of
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