g the digging of trenches in the
streets of a city where the texture of the soil varied continually from
clay to sand and even to gravel, all saturated with subsoil water into
which wells could have been dug. It was very striking to see how the
coarseness of the material affected the quantity of water that had to be
pumped from the trenches,--the finest sand requiring only one hand pump
at a time, while the coarse gravel required either a dozen men or a
steam pump to keep a short trench reasonably free from water. The same
conditions exist when a well is in operation, modified by the fact that
the coarse material yielding a larger supply will be most quickly
exhausted unless the area drained is very large.

A shallow well is most uncertain as to its quantity and is likely to be
of doubtful quality. There are, however, some examples of shallow well
supplies which furnish large amounts of water; as, for instance, the one
at Waltham, Massachusetts, or at Bath, New York,--the latter, a dug well
some twenty feet in diameter and about twenty-eight feet deep,
furnishing a constant supply of good water to a village of about 4000
people.

_Construction of dug wells._

The construction of shallow wells requires little comment. Ordinarily,
they are dug down to the water, or to such a depth below the level of
the water as is convenient, by the use of an ordinary boat pump to keep
down the water, and then are stoned up with a dry wall. Such a well for
a single house requires an excavation of about eight feet diameter, with
an inside dimension of about five feet.

[Illustration: FIG. 27.--Mode of sinking a well.]

If the soil at the bottom of the well is sandy, it is possible to take a
barrel or a large sewer pipe and sink it into the bottom of the well in
the water by taking out material from the inside and loading the outside
to keep it pressed down into the sand. This same plan may be used to
sink the whole body of the well wall, first supporting the lower course
of masonry on a curb, so called (see Fig. 27). This curb is usually made
of several thicknesses of two-inch plank well nailed together, the plank
breaking joints in the three or four layers used. It is a good plan to
have this shoe or curb extend outwardly beyond the walls of the well so
that some clearance may be had, otherwise the dirt may press against the
walls so hard as to hold it up and prevent its sinking. While this
arrangement may be put down in water, it r