318 LOGGING 
two latter cases have piles driven to bed rock, one being placed 
under the base of each leg, and cut off 2 or 3 feet above high- 
water mark. 
Stringers, ties and guard rails are used as on a pile trestle, 
and the bents are braced in the same manner. 
Framed trestles often are put together on the ground and raised 
to a vertical position by means of a hoisting or yarding engine 
and suitable blocks and tackle. Trestles 132 feet in height and 
600 feet long have been erected in this manner. This procedure 
reduces the amount of top work necessary and makes it possible 
to use less skilled labor than would be required if the bents were 
framed in the air. Standardized framed trestle structures have 
been designed for use on lines where frequent changes in roadbed 
are necessary. The structure is built in sections or units which may 
be taken down and readily placed in a new structure without 
reframing. This practice, however, is not followed extensively 
in logging railroad construction. 
Cost of Trestles. — Framed trestles are frequently built by 
contract, the price being regulated by the amount of timber used 
and the height of the trestle. Payment for pile trestles, when 
built by contract, is made on the basis of the number of piles 
driven and the amount of sawed timber used in the remainder 
of the structure. 
Truss Bridge. — This type of bridge is not in common use 
although some have been built where the conditions were un- 
favorable for the erection of pile or framed trestles. 
Dunnage or Dust Road. — This is a type of a cheap logging 
road employed for spurs in the cypress swamps of Louisiana 
where the bottom is too soft for dirt ballast, and the cost of 
a pile road is not warranted by the amount of timber to be re- 
moved. 
The construction of a dunnage road is preceded by clearing 
a right-of-way from 15 to 20 feet wide from which all brush is 
cut and stumps removed from the line of the roadbed. The latter 
is covered with small poles 5 or 6 inches in diameter, laid close 
together, lengthwise of the right-of-wa5\ These give a wide 
bearing surface and serve as a bed on which the ballast is 
placed. The crossties are laid on the poles and the rails spiked 
to them. The track is then ballasted with bark, edgings, saw- 
dust and other sawmill refuse which is brought from the mill 
