ater from passing through, so long as it is kept wet, as
effectually as a yard will do."

"If," says Gisborne, "you eat off turnips with sheep, if you plow
the land, or cart on it, or in any way puddle it, when it is wet,
of course the water will lie on the surface, and will not go to
your drains. A four-foot drain may go very near a pit, or a
water-course, without attracting water from either, because
water-courses almost invariably puddle their beds; and the same
effect is produced in pits by the treading of cattle, and even by
the motion of the water produced by wind. A very thin film of
puddle, always wet on one side, is impervious, _because it cannot
crack_."

In those four words, we find an allusion to the whole mystery of the
drainage of clays--a key which unlocks the secret by which the toughest
of these soils may be converted, as by a fairy charm, to fields of
waving grain.

CRACKING OF CLAYS BY DRYING.

"In drying under the influence of the sun," says Prof. Johnston, "soils
shrink in, and thus diminish in bulk, in proportion to the quantity of
clay, or of peaty matter, they contain. Sand scarcely diminishes at all
in bulk by drying; but peat shrinks one-fifth in bulk, and strong
agricultural clay nearly as much." By laying drains in land, we take
from it that portion of the water that will run out at the bottom. The
sun, by evaporation, then takes out a portion at the top. The soil is
thus contracted, and, as the ends of the field cannot approach each
other, both soil and subsoil are torn apart, and divided by a network
of cracks and fissures. Every one who is familiar with clay land, or who
has observed the bottom of a ditch or frog pond by the roadside, must
have observed these cracks, thus caused by the contraction of the soil
in drying. The same contraction occurs in drier land, by cold, in
Winter; by which, in cold regions, deep rents are made in the earth, and
reports, like those of cannon, are often heard. The cracking by drying,
however, is more quiet in its effects, merely dividing the ground,
noiselessly, into smaller and smaller masses, as the process proceeds.
Were it not for this process, it may well be doubted whether clay lands
could be effectually drained at all. Nature, however, seems to second
our efforts here, for we have seen that the stiffer the clay, the
greater the contraction, and the more the soil is split up and rendered
permeab