hen the resultant pressure is not vertical on the piers these
must be constructed to meet the inclined pressure. In any stiffened
suspension bridge the action of the pier will be analogous to that of a
pier between two arches.

_Concrete in a shell_ is a name which might be applied to all the methods
of founding a pier which depend on the very valuable property which strong
hydraulic concrete possesses of setting into a solid mass under water. The
required space is enclosed by a wooden or iron shell; the soil inside the
shell is removed by dredging, or some form of mechanical excavator, until
the formation is reached which is to support the pier; the concrete is then
shot into the enclosed space from a height of about 10 ft., and rammed down
in layers about 1 ft. thick; it soon consolidates into a permanent
artificial stone.

_Piles_ are used as foundations in compressible or loose soil. The heads of
the piles are sawn off, and a platform of timber or concrete rests on them.
Cast iron and concrete reinforced piles are now used. _Screw piles_ are
cast iron piles which are screwed into the soil instead of being driven in.
At their end is fixed a blade of cast iron from two to eight times the
diameter of the shaft of the pile; the pitch of the screw varies from
one-half to one-fourth of the external diameter of the blade.

_Disk piles_ have been used in sand. These piles have a flat flange at the
bottom, and water is pumped in at the top of the pile, which is weighted to
prevent it from rising. Sand is thus blown or pumped from below the piles,
which are thus easily lowered in ground which baffles all attempts to drive
in piles by blows. In ground which is of the nature of quicksand, piles
will often slowly rise to their original position after each blow.

_Wells._--In some soils foundations may be obtained by the device of
building a masonry casing like that of a well and excavating the soil
inside; the casing gradually sinks and the masonry is continued at the
surface. This method is applicable in running sands. The interior of the
well is generally filled up with concrete or brick when the required depth
has been reached.

_Piers and Abutments._--Piers and abutments are of masonry, brickwork, or
cast or wrought iron. In the last case they consist of any number of hollow
cylindrical pillars, vertical or raking, turned and planed at the ends and
united by a projection or socket and by flanges and bolts. The pillars are