-and-one-quarter inch
pipe, with its lower end closed and pointed, and driving it with wooden
mauls into the ground. When it has gone six or eight feet, it is pulled
up, cleared from the earth, and replaced, to be driven six feet again.

[Illustration: FIG. 31.--Well-drilling apparatus.]

With ordinary soil, the pipe is easily withdrawn with a chain wrench,
and two men will drive one hundred feet in a couple of days. When water
is reached, a well point is put on through which water may percolate
without carrying too much soil. This type of well is suitable for use in
soft ground or sand, up to depths of about one hundred feet, and in
places where the water is not abundant. It is most useful for testing
the ground to see where water may be found and by pumping from such a
well to see what quantity of water may be expected. This type is often
used as a shallow well, and the author has seen such wells driven only a
dozen feet. Such a well has no protection against pollution, and an
ordinary dug well is better for shallow depths. A driven well always has
a disadvantage also from the ever present danger that the iron pipe will
rust through at the top of the ground water and so admit to the well the
most polluted part of the drainage.

For larger supplies and for greater depths, a machine like a pile-driver
has to be used for forcing down the pipe. This is not usually removed,
but driven down as far as possible, and when the limit of the machine
has been reached, a smaller size is slipped down inside the driven pipe,
to be in turn driven to refusal. In rock, that is, if the well has to
penetrate a layer of rock, a drill is used that will work inside of the
pipe last driven, and by alternately lifting and dropping the drill, and
at the same time twisting it back and forth, a hole through rock may be
made many hundred feet below the surface of the ground. Figure 31 shows
a cut of a common type of well-drilling machine.

In some soils, not rock, it is necessary to keep the drill going in
order to churn up or soften the earth so that the pipe may be lowered.
The churned-up soil is removed by a sand pump, which is a hollow tube
with a flap valve at the lower end opening inwards and a hook on the
upper end. By alternately drilling, pipe-driving, and pumping the wet
material, length after length of pipe can be forced into the ground
until water of a satisfactory quantity is reached. Very often a jet of
water is used to wash out t