sistance, but
the constant pressure together of the sides, even when it does not
produce a fracture of the soil, catches hold of the feet of the
tile, and breaks it through the crown. When the Regent's Park was
first drained, large conduits were in fashion, and they were made
circular by placing one horse-shoe tile upon another. It would be
difficult to invent a weaker conduit. On re-drainage, innumerable
instances were found in which the upper tile was broken through the
crown and had dropped into the lower."

Another form of tiles, called _sole-tiles_, or _sole-pipes_, is much
used in America, more indeed than any other, except perhaps the
horse-shoe tile; probably, because the first manufacturers fancied them
the best, and offered no others in the market.

In this form, the sole is solid with the tile. The bottom is flat, but
the bore is round, or oval, or egg-shaped, with the small end of the
orifice downward.

[Illustration: Fig. 31--SOLE-TILE.]

The sole-pipe has considerable advantages theoretically. The opening or
bore is of the right shape, the bottom lies fair and firm in place, and
the drain, indeed, is perfect, if carefully and properly laid.

The objections to the sole-pipes are, that they are somewhat more
expensive than round pipes, and that they require great care in placing
them, so as to make the passage even from one pipe to another.

A slight depression of one side of a pipe of this kind, especially if
the bore be oval or egg-shaped, throws the water passage out of line. In
laying them, the author has taken the precaution to place under each
joint a thin piece of wood, such as our honest shoe manufacturers use
for stiffening in shoes, to keep the bottoms of the pipes even, at
least until the ground has settled compactly, and as much longer as they
may escape "decay's effacing finger."

COLLARS for tiles are used wherever a sudden descent occurs in the
course of a drain, or where there is a loose sand or a boggy place, and
by many persons they are used in all drains through sandy or gravelly
land.

[Illustration: Fig. 32.--PIPES AND COLLAR.]

The above figure represents pipe-tiles fitted with collars. Collars are
merely short sections of pipes of such size as to fit upon the smaller
ones loosely, covering the joint, and holding the ends in place, so that
they cannot slip past each other. In very bad places, small pipes may be
entirely sheathed in larg