on of the auger is
intermittent. After a few revolutions it is raised and emptied, the
soil clinging between the spirals. Depths to 50 or 60 ft. are usually
bored by hand; deeper holes by horse power. For sandy, non-cohesive
soils, the auger may be encircled by a close-fitting sheet-iron
cylinder to prevent the soil from falling out.

Pod augers generally vary in diameter from 8 to 20 in. A common form
(fig. l) consists of two curved iron plates, one attached to the rod
rigidly, the other by hinge and key. By being turned through a few
revolutions the pod is filled, and is then raised and emptied. For
boring in sandy soils, the open sides are closed by hinged plates.
Fig. 2 shows another type of pod auger. For holes of large diameter
earth augers are handled with the aid of a light derrick.

[Illustration: FIG. 1. FIG. 2. Pod Auger.]

2. _Drive pipes_ are widely used, both for testing the depth and
character of soft material overlying solid rock and as a necessary
preliminary to rock boring, when some thickness of surface soil must
first be passed through. In its simplest form the drive pipe consists
of one or more lengths of wrought iron pipe, open at both ends and
from 1/2 in. to 6 in. diameter. When of small size the pipe is driven
by a heavy hammer; for deep and large holes, a light pile-driver
becomes necessary. The lower end of the pipe is provided with an
annular steel shoe; the upper end has a drivehead for receiving the
blows of the hammer. Successive lengths are screwed on as required.
For shallow holes the pipe is cleaned out by a "bailer" or
"sand-pump"--a cylinder 4 to 6 ft. long, with a valve in the lower
end. It is lowered at intervals, filled by being dashed up and down,
and then raised and emptied. If, after reaching some depth, the
external frictional resistance prevents the pipe from sinking farther,
another pipe of small diameter may be inserted and the driving
continued. Drive pipes are often sunk by applying weights at the
surface and slowly rotating by a lever. Two pipes are then used, one
inside the other. Water is pumped down the inner pipe, thus loosening
the soil, raising the debris and increasing the speed of driving. The
"driven well" for water supply is an adaptation of the drive pipe and
put down in the same way.

[Illustration: FIG. 3. Drill Bit.]

[Illustration: FIG. 4. Rod Joint.]

3. _Drill and Rods._--T