RAILROAD CONSTRUCTION 
319 
in "dunnage" cars. The dunnage is dumped on either side 
of the rails, then thoroughly tamped under the ties and, when the 
track is leveled up, it is ready for operation. Light-weight 
locomotives, from 18 to 30 tons, are used because this type of 
roadbed will not stand heavy traffic. 
Cribwork. — A crib foundation may be used when logging 
railroads cross low places that are too soft for a fill, and where 
the lumber company is not prepared to put in piling. Logs 18 or 
24 inches in diameter and 16 or 18 feet long are placed across 
the right-of-way at intervals of 8 feet. On top of these, and 
parallel to the roadbed, round stringers from 18 to 24 inches in 
Phot 
Fig. 104. — A Crib Bridge on a Logging Railroad Spur. A cheap method 
of spanning shallow depressions. Louisiana. 
diameter are placed 56| inches, center to center. These are 
notched into the cross-skids and drift bolted to them. The 
crossties are then laid on top of these stringers. The cross- 
skids are given a greater bearing surface by placing "shims" or 
poles from 4 to 6 inches in diameter and 8 or 10 feet long at 
right angles under them. 
Cribbed bents, similar to those shown in Fig. 104, are some- 
times used on spur lines to span shallow depressions because they 
can be rapidly constructed at a low labor cost. They are now 
seldom used when a structure more than a few feet in height is 
erected because of the large amount of timber required to con- 
struct them. 
Corduroy for Logging Roads. — Loggers in the South often 
corduroy unballasted spur tracks on wet ground with 16- or 20- 
foot poles from 4 to 12 inches in diameter (Fig. 105). The poles 
are placed between each tie and project out far enough on either 
