770. Quay-walls with us are ordinarily made either by form-
ing a facing of heavy round or square piles driven in juxtaposition,
which are connected by 1 or zo tal p eces and see re 1 from the
pressure of the earth hJIed in bel d them by It d t eg ; or, by
placing the pieces h zontally j o each other a d securing
them by iron bolts. La d ties a e se 1 to courteract the pres-
sure of the earth or ri bb si wh c! s tl own behind them to
form the surface of tie quaj A otler mode of co istruction,
which is found to be strong and durable, is in use m our Eastern
seaports. It consists in making a kind of crib-work of large
blocks of granite, and filling in with eartli and stone rubbisn.
The bottom course of the crib may be laid on the bed of the
river, if it is firm and horizontal ; in the contrary case a strong
grillage, termed a cradle, must be made, and be sunk to receive
the stone work. The top of the cradle should be horizontal, and
the bottom should receive the same slope as that of the bed, in
order that when the stones are laid they may settle horizontally.
777. Dikes. To protect the lowlands bordering the ocean from
inundations, dikes, constructed of ordinary earth, and faced to-
wards the sea with some material which will resist the action of
the current, are usually resorted to.
