In countries where floods or very heavy and sudden rainfall, frost and snow quickly succeed, masonry or dry stone retaining walls at the foot of a slope soon become impaired, and require constant supervision and careful maintenance, and cannot be considered as economically or generally effectual; and should the earth settle, as they are comparatively solid they will not follow any subsidence of the surface; therefore cracks occur and water accumulates in the hollows, the slope has no longer uniform support, a localization of the egression of water is caused, owing to the fissures in the wall inducing a flow, and the wall becomes a cause of a slip instead of a protection against movement. Should such a wall bulge after it has been restored to the condition of being a continuous support, its forward movement may be arrested by the erection of counterforts with an inclined face in front from 10 to 30 feet apart according as weak places exist, having joints at right angles to the batter; and this is, perhaps, the cheapest and quickest remedy, but the slope must be carefully drained and the number of weep-holes be increased. In order not to obstruct, but induce the through drainage of water, retaining walls to prevent slips have been erected, consisting of arches turned upon piers, the intervening space being dry walling which allows a free flow of water, the idea being to afford the necessary support without interfering with the drainage. In some cases, as it tends to condense the soil, weighting the toe of the slope may prevent movement, and on the side of a hill weight and mass, apart from slope protection or drainage, must be provided to arrest a slip or prevent further movement, either by means of a continuous wall, or by the addition of frequent counterforts, 5 or 6 feet in width, to an existing wall, if space permits, the back and front having a considerable batter: the centre of gravity of such a mass being low and the base large, overturning is improbable. Forward movement can be also guarded against by deep foundations, and as the earth will rest on the inside they can have a flatly inclined base sloping towards the cutting, as it will tend to prevent overturning, the depth of the foundations at the face being two or three times that at the back. Such a structure can hardly be called a wall, being really an extensive and massive concrete toe. Perhaps generally the most economical and secure way of preventing movement is to erect a low Portland cement concrete wall at the toe of a slope with a considerable batter; or to cut a trench at formation level outside the line of the slope, and to shore it by means of old sleepers strutted at intervals when better and durable material cannot be readily obtained.