224 
LOGGING 
being fastened to a stump at the rear. Both the head spar and 
tail spar tree are guyed with four lines. 
The trolley or carriage is triangular in shape with two 16- by 
3-inch sheaves; with a clevis at the apex to which chokers are 
attached; and also with a clevis on each edge of the block to 
which the haul-back and haul-in lines are attached. The trolley 
is drawn towards the head spar by means of a haul-in line which 
passes from a drum on the engine up to and through a block 
Fig. 69. — The MacFarlane Skyline System of Overhead Power Logging. 
on the head spar and is then fastened to a clevis on the side of the 
trolley next to the spar tree. The trolley is drawn out towards 
the tail tree by means of a haul-back line which leads from a 
drum on the engine, through blocks placed at one side of the run, 
to a block on the tail tree or to some other convenient point of 
attachment, and is then brought back and fastened to a clevis 
on the side of the trolley next to the tail spar tree. 
When skidding is in progress the main cable is pulled taut, 
and the trolley drawn out to the desired point by means of the 
haul-back line. The main cable is then slacked off until the trolley 
is lowered to the ground. The trolley and main cable are then 
dragged to the log if it is at one side of the center of the run. 
When the log has been fastened to the trolley by means of chokers, 
the main line is tightened and held in place by powerful drum 
brakes and the log brought to the head spar tree by the haul-in 
