The degree of slope of a railway cutting must be regulated by the nature of the material excavated. A slope of 1½ to 1, which gives for every foot of vertical height a width of one foot 6 inches of horizontal base, as in Fig. 48, is usually adopted for cuttings in ordinary earth, good clay, sand, or gravel. There are some descriptions of strong clay and marl which will stand at a steeper slope, even at 1 to 1; but, on the other hand, there are some kinds of clay which must ultimately be taken out to 2 to 1, and even 3 to 1. It frequently occurs that the slopes of a clay cutting, taken out to 1½ to 1, appear to stand well for a time, but after exposure to the frost and rain of one or two seasons, the material becomes loosened, and forms into slipping masses, which slide down on to the line, stopping all traffic, and have to be cleared away before train operations can be resumed. Cuttings through solid rock may be taken out to a slope of ¼ to 1, as shown in Fig. 49, provided the material is compact, and there is not too great a dip in the strata or rock-beds. Where the rock-beds lie at a considerable angle, the slope on the high side will have to be made flatter than the slope required on the low side, as shown in Fig. 50, and great care must be taken to remove from the high side all loose or disconnected pieces of rock which might come away and slide down on to the line. [Illustration: Fig. 47, 48, 49, 50, 51] Strong dry chalk will generally stand at a slope of ⅓, or ½ to 1, but when wet and mixed with flints it will be necessary to increase the slope to not less than ¾ to 1. Where the rock is loose and disintegrated, a slope of not less than ½ or ¾ to 1 will be required, 63 and at many points there will be detached threatening masses of rotten rock which must be cleared away to a much flatter slope for safety. In cuttings of this description it is frequently found necessary to clear out a portion of the loose pieces of the lower cavities and build in their place a facework of masonry to support the superincumbent rock. Springs of water rising in the rock, or running over any part of the rock slopes, must be properly provided for, and conducted to the nearest channel. They should be carefully watched during the winter season, when the frost, acting on the water penetrating the crevices, splits and separates large pieces which were previously firm and secure.