downward and distributing them more equally
through the whole, should render the soil more porous.

Another cause of the retention of water by the surface soil, often a very
serious one, is the puddling which clayey lands undergo by working them,
or feeding cattle upon them, when they are wet. This is always injurious.
By draining, land is made fit for working much earlier in the spring, and
is sooner ready for pasturing after a rain, but, no matter how thoroughly
the draining has been done, if there is much clay in the soil, the effect
of the improvement will be destroyed by plowing or trampling, while very
wet; this impervious condition will be removed in time, of course, but
while it lasts, it places us as completely at the mercy of the weather as
we were before a ditch was dug.

In connection with the use of the word _impervious_, it should be
understood that it is not used in its strict sense, for no substance which
can be wetted by water is really impervious and the most retentive soil
will become wet. Gisborne states the case clearly when he says: "Is your
subsoil moister after the rains of mid-winter, than it is after the
drought of mid-summer? If it is, it will drain."

The proportion of the rain-fall which will filtrate through the soil to
the level of the drains, varies with the composition of the soil, and with
the effect that the draining has had upon them.

In a very loose, gravelly, or sandy soil, which has a perfect outlet for
water below, all but the heaviest falls of rain will sink at once, while
on a heavy clay, no matter how well it is drained, the process of
filtration will be much more slow, and if the land be steeply inclined,
some of the water of ordinarily heavy rains must flow off over the
surface, unless, by horizontal plowing, or catch drains on the surface,
its flow be retarded until it has time to enter the soil.

The power of drained soils to hold water, by absorption, is very great. A
cubic foot of very dry soil, of favorable character, has been estimated to
absorb within its particles,--holding no free water, or water of
drainage,--about one-half its bulk of water; if this is true, the amount
required to _moisten_ a dry soil, four feet deep, giving no excess to be
drained away, would amount to a rain fall of from 20 to 30 inches in
depth. If we consider, in addition to this, the amount of water drained
away, we shall see that the soil has sufficient capacity for the reception
of all