RAILWAY CONSTRUCTION. 63 



required, 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 face work 

 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 pre- 

 viously firm and secure. 



Instances will occur where a cutting has to be made through 

 a thick bed of rock and several feet of soft loose strata under- 

 neath. The effect of forming a cutting through the soft strata is 

 to induce the heavy bed of rock above to squeeze or force out 

 the softer material below, and unless proper means were taken 

 to avert such a disturbance, the entire cutting would have to be 

 excavated to a very flat slope. The method adopted in such a 

 case is to build strong face-walls of masonry, brickwork, or con- 

 crete, underneath the rock, as shown in Fig. 51, with strong 

 inverts placed at short distances. Suitable arrangements must 

 be made to take away the drainage water which will collect at 

 the back of the walls, and weeping-holes or outlets must be left 

 in the lower part of the walls to convey the water into the water- 

 tables on the line. 



Where there is a depth of earth cutting on the top of the 

 rock, the earth should be cut away so as to leave a bench or 

 space of 3 or 4 feet between the edge of the rock cutting 

 and the foot of the earth slopes, as shown on Fig. 52. 



In cases of shelving rock, with earth or clay on the top, as 

 shown in Fig. 53, it is frequently found necessary to remove the 

 whole of the clay on the high side to prevent the possibility of 

 its sliding off the rock on to the line below. 



In large cuttings it is usual to push forward a gullet of 

 sufficient width for one or two lines of waggons, as shown in 

 Fig. 54. When this has advanced some distance, strong planks 

 or half balks of timber are placed across the gullet, and the sides 

 or wings of the cutting can be excavated, the material wheeled 

 to the gullet, and tipped from the barrows into the waggons 

 beneath. By this arrangement the work can be carried on very 



