RAILWAY CONSTRUCTION. 227 



undergo a complete change, developing into soft masses contain- 

 ing too much clay to allow the water to pass through readily. 

 Where rock is scarce and gravel plentiful, the lower layer may 

 be made of the heavier or coarser gravel, leaving the finer gravel 

 for the upper layer, or boxing ; but there is no doubt that the 

 broken stone pitching makes the most efficient bottom layer. 

 No gravel ballast should be used which is not free from clay or 

 earthy sand. 



Wherever there are particles of earthy matter, sufficient to 

 furnish nourishment for vegetable growth, weeds will quickly 

 spring up, and once established are most difficult, if not impos- 

 sible, to eradicate. The presence of weeds checks drainage, and 

 gives an untidy appearance to the line, besides constantly 

 occupying a large portion of the platelayers' time in their 

 removal. 



Clean cinders, free from dust or earth, are much used for 

 upper ballast and boxing, and being lighter than gravel, are 

 specially applicable for soft boggy ground. Burnt clay, broken 

 into small pieces, has been largely adopted in districts where 

 both rock and gravel were difficult to obtain. Chalk, furnace- 

 slag broken small, crushed brick and sand, are frequently used 

 as ballast. Sand is objectionable where there is high-speed 

 traffic, as the finer particles rise in the form of dust and deposit 

 themselves on the vehicles and machinery of the train. 



The water-tables, or side drains in the cuttings, should be 

 cut below the formation level, and to a depth or width sufficient 

 to take away all rain-water, or water arising from springs. 

 Where the material of the cutting is of a loose friable nature, it 

 may be necessary to protect the sides of the water-tables with 

 low dry stone walls, as in Fig. 338 ; or glazed earthenware pipes 

 may be laid, as in Fig. 339, with open joints, or with grate 

 openings at regular intervals. In some cases substantial side- 

 walls and invert are requisite to carry away the flow of water. 



Timber sleepers intended for the flange railroad should have 

 the rail-seats grooved by machinery to ensure perfect accuracy 

 in the position of the grooves, and in the angle or inclination of 

 the rail-seats. Fig. 340 is a side view of part of a sleeper 

 grooved to receive a flange rail. The presence of the grooves 

 materially facilitate the laying of the rails to gauge, but must 

 not be allowed to interfere with the constant use of the plate- 

 layer's gauge. In a similar manner the timber sleepers for the 



