For a set of soil samples. Percy collected soil from three different
strata. The first sample represented the surface stratum from the
top to six and two-third inches; the second sample represented the
subsurface stratum from six and two-thirds to twenty inches; and the
third sample represented the subsoil from twenty to forty inches,
each sample being a composite of about twenty borings.

In collecting these the hole was bored to six and two-third inches
and somewhat enlarged by scraping up and down with the auger, all of
the soil being put into a numbered bag. Then, the hole was extended
and the subsurface boring removed without touching the surface soil.
This boring to a depth of twenty inches was put into a second bag.
The hole was then enlarged to the twenty-inch depth but the
additional soil removed was discarded as a mixture of the surface
and subsurface strata. Finally the hole was extended to the
forty-inch depth and the subsoil from one groove of the auger was
put into a third bag. In this manner about an equal quantity of soil
was bagged from each stratum; and twenty such borings taken with an
auger about one inch in diameter make a sufficient quantity to
furnish to the chemist.

"Of course the surface soil is by far the most important," Percy
explained. "It represents just about the depth of earth that is
turned by the plow in good farming on normal soils; and it weighs
about two million pounds per acre. The subsurface stratum extending
from six and two-thirds to twenty inches in depth represents the
practical limit of subsoiling; and this stratum weighs about four
million pounds; while the subsoil stratum weighs about six million
pounds, where the soil is normal, such as loam, silt loam, clay