FOUNDATION of Bridges, is laid after different manners. The first is by inclosing all round the space of ground you would build upon, by dams made with piles set deep in the ground in double rows, well strengthened and bound together with cross pieces and cords, and filling the vacant spaces between them with chalk or other earthy matter. This being done, the water must be emptied out, and the foundation dug according to the quality of the ground, driving down piles, if it be necessary, upon which the walls of the foundation must be laid. But this method is only practicable in building on such rivers, where the water is neither very rapid, nor very deep. The second is done by laying the foundation on grate-work, rafts of stout oak well bound together, and made fast at the surface of the water with cables or machines, and building upon them large quarters of stone, cramped together, and joined with good mortar, or cement, and afterwards letting them descend softly by these cables and ma-
chines perpendicularly to the bottom of the water. This was the method practised in laying the foundation of Westminster Bridge, the grating being made of the bottom of a frame called by the French Caillon, the sides of which were so contrived, that they might be taken off, after a pier was finished. The third is by drawing off all, or the greatest part of the water of the river into some other place.