Chap. XXV.

ON STONE BRIDGES.

1517

upper portion of the wall is terminated by the talus of the slope, which is generally facedwith masonry for some distance; its lower extremity is cut vertically at A, that it mayhave the requisite solidity at this part.

Fig. 2778. shows the wing-walls, as set out perpendicularly to the axis of the bridge.This arrangement does not allow so free a passage for floods, and ought only to be adoptedwhen the natural banks of the river are not subject to injury from the running of the water.

"When the river flows through a soil easy to be washed away, it is necessary to confinethe bed where the bridge is situated. To do this we must construct embankments at thequays paved with stone, and continue them to such a distance above and below thebridge as may be necessary : the quays of several bridges, as that at Moulins, on the Allier ,

c ba

Fig. 2778.

Fig. 2779. BRIDGE AT MOULINS.

are so arranged : A B is a splay joining the bridge with the road, B C is a return wallparallel to the axis of the bridge, D, D show the paved slope at the abutments, the toe ofwhich is strengthened by two rows of piles, between which rubble-work is laid.

In cities, bridges are usually accompanied with quay-walls; the angle formed by theirintersection with the bridge obstructs the passage of carriages, and is generally cut offby a straight or curved line, as at A; the angle formed by the quay-wall A B and thebridge is curved, and the projection occasioned by such an arrangement supported by agathering over of the masonry.

At the bridge of Neuilly , the portion of the quay-wall AB unites the width of the bridgewith that of the road, and the return wall B C is in the line with the edge of the footway,the interval between the two pedestals C and D answering to. its width, and the quay-walls C,D are prolonged to a considerable distance, sustaining the road G G. Toallow the passage for the towing-horses a tunnel and a road E E is constructed beyondthe abutment.