An inclined water-bearing stratum between rock loosely bedded and inclined towards a cutting, unless drained and supported, will probably cause a slip consequent upon the action of water or frost; on the other hand, veins may alone hold the masses together, and, therefore, when they are affected the cementing medium is destroyed; however, inclined water seams are a frequent cause of slips, for where any water-bearing earth meets a closer and consequently less pervious stratum, damp surfaces are produced, and an unstable condition; consequently, mixtures of rock, clay, and sand, are usually troublesome. Also in a cutting in sidelong ground if a stratified rock dips parallel, or nearly so, to the slope of a hill, slips are probable, as it may slide towards the cutting. Similarly, in a cutting in drift or alluvial soil, or any that will quickly weather, resting upon rock, especially should it have a smooth bed inclining towards the formation, the superimposed earth will usually be unstable, and even the act of penetrating the top stratum, or the erection of a retaining wall or the weight of a small embankment upon it, may cause it to move; and when motion has commenced it is difficult to arrest it; and should water trickle upon the surface of the rock, it may cause the upper stratum to slide; also when water flows or remains upon rock having a superimposed bed of shale or clay, the top stratum may not remain at rest even though the surface of the rock may be nearly level and practically waterproof, and where rock beds overlie shale which is liable to become softened by time and water and to perish, particularly when the beds are twisted or contorted; as, for instance, limestone or sandstone upon shale or marly-shale, the latter becoming softened by the action of the atmosphere, water, or frost will form a sliding medium upon which the rock may move, or should shale overlie rock, as it frequently does, it may slide upon the hard surface. All alternate beds of shale or any softer earth than the rock, particularly broken shales when found mixed with sand and clay and the lias shales, and rock should be regarded as treacherous and liable to slip. Also some of the slate rocks, as they frequently have veins of limestone, &c., and as the latter decomposes it mixes with the clay and becomes of a marly character. Dark blue shale or indurated slaty clay is sometimes difficult to excavate, but when exposed to atmospheric and aqueous action it breaks into pieces and becomes little better than a treacherous clay. The cohesion of shale becomes less as it approaches a greasy clayey condition, and, therefore, one readily affected by water or air, and it may then not stand at a steeper slope than 3 to 1. Rock and shale, which may stand at a steep inclination provided the beds are horizontal, it has been found, do not permanently repose when they dip towards a cutting until as flat a slope as 2 to 1 is given; and where