392 
LOGGING 
to 1 vertical. The dam should be at least 8 feet wide on top. 
Two thicknesses of 3-inch plank or hewed poles are spiked on the 
sloping face, the joints being alternated and the whole covered 
with a bed of gravel. The rear mud-sill is protected by toe- 
Photograph by H. R. McMillan. 
Fig. 133. — The Sluiceway and Apron of a Rafter Dam on the Priest River. 
Idaho. 
spiling driven down to hard clay or bedrock, and the cribs are 
weighted down with stone. 
The frame for a rafter dam is frequently supported on round 
or squared tmibers instead of cribwork. 
Pile Dam. — The buttresses and wings of this type of dam are 
formed by a double row of piles driven to bedrock, the space 
