RAILROAD CONSTRUCTION 
317 
18 inches in diameter or 10- by 12-inch, or 12- l)y 12-inch squared 
timljers. On a standard-gauge road two of the legs are vertical 
and 36 inches apart, while the other two legs are given a batter 
of from 2 to 3 inches for each foot of height. The legs rest on 
a timber called a sill to which they are drift bolted. Sills vary 
in length according to the height of the trestle and project about 
■ The Pole Foundation for a Dunnage Ivoad in a Cypress .Sw ani]). 
Louisiana. 
2 feet beyond the base of the outer legs. The tops of the legs 
are covered with a cap 12 or 14 feet long on which the stringers 
rest. 
Framed bents may rest on mud sills, or on piles. When the 
former are used they are frequently 3 by 12 inches by 4 feet in 
size and are placed at right angles to the bent, and a sufficient 
number are used to provide a greater bearing surface than that 
offered by the main sill. Mud sills are suited for a bottom solid 
enough to provide a firm support but they are not adapted to 
use in swamps or stream beds. The foundations used in the 
