Should an embankment have to be tipped upon rock, care must be taken to prevent the surface water flowing under its base, and to counteract sliding movement the ground should be benched and a drain made on the higher side; also in a deep cutting the slope or face should be stepped, or have a cess at about mid-height, or where desirable, to lessen the effect of the trickling of the surface water and to prevent a flow in a direct line, which might make the velocity of any leakage waters dangerous, especially after a rapid thaw. On a mid-cess a catchwater drain should be cut to intercept the surface water, which may not percolate but flow upon the slope, and, unless diverted and conducted to an outlet, may saturate or erode the bottom. Before a cutting in drift soil upon the side of a hill can be drained, it may be necessary to sink a shaft upon the higher side some distance from the slope and construct a complete series of drains under the formation. Also should an embankment in sidelong ground be near to a river, the exposed river-bank face must be protected, and in any case, when a pier of a bridge has to be placed close to the edge of a rock, the face of the earth should be preserved by a substantial Portland cement concrete covering in order to prevent disintegration culminating in a slip or subsidence. In setting out a line of railway or a canal care should be taken to avoid, if practicable, either cuttings or embankments in soil resting upon inclined rock, as slips are almost sure to occur. However, should it be unavoidable, their depth and height should be reduced to a minimum and, if possible, the formation be raised until the bare rock crops out, and this can frequently be effected within the limits of deviation. Also deep cuttings in clay or earth, having particles soon affected by weather, should be avoided, but they may be necessary; and should any have to be located upon a sharp curve, it is advisable to excavate the projecting spur on the convex side of the curve more than that required to obtain the formation width, as it is peculiarly exposed, and therefore more likely to slip. When cuttings are upon the escarpment of a clay hill the slope upon the valley side need not be so flat as that against the hill. An inclination of 3 or 4 to 1 may be necessary upon the hill-side, whereas a 1½ to 1 slope may be sufficient upon the other. When a slip may involve the destruction or injury of any adjacent buildings, the best plan is to erect a retaining wall at the foot of a slope, not less than about one-fourth of the height of an embankment or the depth of a cutting, ample provision being made for drainage and the expansion of the earth. It is a sure protection and support, and the consequences of a slip may be most serious in such a position. The protection of the slope and a breast wall may, however, be alone necessary upon the valley-side.