provided, the place
of any obstruction may readily be determined, at a glance into them.

Upon our own land, we have had two or three instances of obstruction by
sand, very soon after the tiles were laid, and always at the junction of
drains imperfectly secured with bricks, before we had procured proper
branch-pipes for the purpose.

A little experience will enable the proprietor at once to detect any
failure of his drains, and to apply the proper remedy. Obstructions from
silt and sand are much more likely to occur during the first season
after the drains are laid, than afterwards, because the earth is loose
about the pipes, and more liable to be washed into the joints, than
after it has become compact.

On the whole, we believe the danger to tile-drains, of obstruction, is
very little, provided good tiles are used, and proper care is exercised
in laying them.

CHAPTER XIX.

DRAINAGE OF STIFF CLAYS.

Clay not impervious, or it could not be wet and dried.--Puddling,
what is.--Water will stand over Drains on Puddled Soil.--Cracking
of Clays by Drying.--Drained Clays improve by time.--Passage of
Water through Clay makes it permeable.--Experiment by Mr.
Pettibone, of Vermont.--Pressure of Water in saturated Soil.

It is a common impression that clay is impervious to water, and that,
therefore, a clay soil cannot be drained, especially by deep
under-drains. A moment's reflection will satisfy any one that such land
is not absolutely impervious. We find such land is wet in Spring, at any
depth; and, in the latter part of Summer, we find it comparatively dry.
How comes it wet, at any time, if water does not go into it? And how
comes it dry, at any time, if water does not come out of it?

In treating of the power of the soil to absorb moisture, we have shown
that a clay soil will absorb more than half its weight and bulk of
water, and that it holds more water than any other soil, with, perhaps,
the single exception of peat.

The facts, however, that clay may be wet, and may be dried, and that it
readily absorbs large quantities of water, though they prove
conclusively that it is not impervious to water, yet do not prove that
water will pass through it with sufficient rapidity to answer the
practical purposes of drainage for agriculture. This point can only be
satisfactorily determined by experiment. It is not necessary, however,
that each farmer should try the experiment for himself;