In foundations of a sandy or silty character, a dock or quay-wall having wells in the cross section to within a few feet of its base filled with rammed light dry material, the width of the bottom nearly approaching that of the depth of water, has been adopted in preference to a solid wall of less thickness, as affording a wider base, greater resistance to overturning, and a reduction of the weight upon the foundations. A slip of the earth backing is frequently caused from insufficient drainage and a consequent accumulation of water behind a wall, producing such pressure that the friction of the weight of the wall upon the foundations is impaired and the support in front insufficient to resist a forward movement, therefore the back drainage should receive due attention. When a dock-wall has been thrust forward by the earth it may be a serious movement, likely to increase and culminate in the destruction of the wall, or be merely a slight lateral settlement. Such slips are usually of considerable length, and have an apex where the greatest forward motion has occurred. The chief remedies consist in securing the foundations, supporting the face, lightening or removing the pressure of the backing, draining the backwaters and preventing their reaching the wall. Provided a wall is intact and not damaged, but solidly and horizontally pushed forward, it need not be taken down, but if vertical subsidence has taken place, or a settlement, at the face only, it is generally of serious importance, and it may be necessary to remove and replace it. When a wall bulges slightly from the pressure of the earth at the back and then ceases to move, the ground behind may have become in a state of permanent equilibrium, and the lateral thrust, which before movement was too great, may be so reduced that in the altered position it may remain stable, provided the void is filled with light porous backing, and the drainage of the earth receives due attention. Counterforts of piles reaching to the level of the ground in front of the face have been adopted to arrest and prevent a forward movement, but when the ground is much disturbed and in a loose state, it is unadvisable to drive piles because of vibration which may induce further motion. Instead of timber pile counterforts, trenches might be cut at intervals along the toe and be filled with quick-setting cement concrete, the filling to follow the excavation as closely as possible, and no unsupported earth to be allowed to remain.