1 66 LOGGING 



to make a solid roadway, or else an abutment of logs is built 

 up on the low side. 



Streams and dry watercourses are bridged with structures 

 made from round timbers. Bridges are the first part of a sled 

 road to weaken. They should be built on a slight downgrade, 

 if possible, in order to facilitate the passage of loaded sleds. The 

 usual type is one whose floor is supported on parallel stringers, 

 from 12 to 15 inches in diameter resting on abutments and piers 

 which are made of logs from 12 to 18 inches in diameter, built 

 up in crib-fashion. The piers are 10 or 12 feet square and are 

 commonly placed from 12 to 16 feet apart, and filled with stone 

 to give them stability. The floor is made of skids from 6 to 10 

 inches in diameter, placed across the stringers close enough to 

 form a solid roadbed, and on these a thick covering of bark is 

 spread to hold the snow, and prevent the sled track from break- 

 ing up when the load passes over it. The skids are held in place 

 by stringers which are laid on top of them, one on each side of 

 the bridge. 



Piers are not adapted for use in a stream bed, because freshets 

 are apt to carry them away. Under such circumstances or where 

 the bridge crosses a wide stream the cribs are placed from 20 to 

 25 feet apart and the stringers are supported between them by 

 piles driven to bed rock at intervals of 8 or 10 feet. 



When the stream is too wide for a single span, the cribs may 

 be built in the water, heavily loaded with stone and provided 

 with a "rake" on the upstream face to divert refuse and ice to 

 either side of the crib. When long spans are employed it is cus- 

 tomary to use five stringers. Deep depressions often are filled 

 with cribbing built up to grade level. 



On roads where the snow drifts badly snowsheds are occa- 

 sionally built in order to keep the road open with a minimum of 

 of hand shoveling. They also are employed on steep pitches to 

 keep the ground free from snow, so that the speed of sleds can be 

 controlled. Snowsheds are built in several different forms one 

 of which is shown in Fig. 40. 



The framework is constructed of poles 6 or 8 inches in diam- 

 eter and heavy brush is placed on the sides and roof to prevent 



