s, and are kept in position by having the earth
tightly packed around them. Care must be taken that no space is left
between the ends of the tiles, as dirt would be liable to get in and
choke the drain. It is advisable to place a sod--grass side down--over
each joint, before filling the trench, as this more effectually protects
them against the entrance of dirt. There is no danger of keeping the
water out by this operation, as it will readily pass through any part of
the tiles.

In _digging the trenches_ it is not necessary (except in very stony
ground) to dig out a place wide enough for a man to stand in, as there
are tools made expressly for the purpose, by which a trench may be dug
six or seven inches wide, and to any required depth. One set of these
implements consists of a long narrow spade and a hoe to correspond, such
as are represented in the accompanying figure.

[Illustration: Fig. 5.

Upton tool.

Spade and hoe.]

With these tools, and a long light crowbar, for hard soils, trenches may
be dug much more cheaply than with the common spade and pickaxe. Where
there are large boulders in the soil, these draining tools may dig under
them so that they will not have to be removed.

When the trenches are dug to a sufficient depth, the bottoms must be
made perfectly smooth, with the required descent (from six inches to a
few feet in one hundred feet). Then the tiles may be laid in, so that
their ends will correspond, be packed down, and the trenches filled up.
Such a drain, if properly constructed, may last for ages. Unlike the
stone drain, it is not liable to be frequented by rats, nor choked up by
the soil working into it.

The position of the tile may be best represented by a figure, also the
mode of constructing stone drains.

[Why are small stones better than large stones in the
construction of drains?

On what must the depth of under-drains depend?]

It will be seen that the tile drain is made with much less labor than
the stone drain, as it requires less digging, while the breaking up of
the stone for the stone drain will be nearly, or quite as expensive as
the tiles. Drains made with large stones are not nearly so good as with
small ones, because they are more liable to be choked up by animals
working in them.[AK]

[Illustration: Fig. 6.

_a_--Tile drain trench.
_b_--Stone drain trench.
_c_--Sod laid on the stone.]

[Describe the principle which regulates these relative depths
and distances.