LOGGING IN THE DOUGLAS FIR REGION. 123 
log travels suspended from a trolley is the characteristic feature. 
This arrangement results in both advantages and limitations. The 
advantages in the main are the reduction of friction and the fact 
that with a structure that costs -very little as compared with a rail- 
road or pole road logs can be yarded for long distances at a uniform 
speed. The limitations are fixed by the strength of the line as 
related to its own weight, the tension that has to be applied, and the 
service required of it. The load imposed by a turn of logs, great as 
it may be at times, is a small part of the normal burden. The tension 
necessary to keep it from sagging to the ground is greater on long 
reaches. That, combined with the weight of the line, in time 
exhausts its tensile powers. 
These considerations, well understood by makers of wire rope 
and machinery, weighed heavily on the layout of the first attempt 
with this system. A thousand feet was the longest reach attempted. 
Trial, however, chiefly inaugurated by loggers under the spur of 
necessity, has demonstrated the practicability of longer reaches. 
Difference in elevation of the two cable supports is the key to the 
matter. This changes the forces on the line greatly, and as much 
of the ground to be logged compels just this arrangement the method 
has of late been successfully employed on two or three times the 
distance originally proposed. Not always, of course, does topog- 
raphy so lend itself. Intervening ridges may cut off the oppor- 
tunity to stretch a cable for a long distance, or at least prevent the 
line from taking the sag which safeguards it. - 
Three methods which are used successfully are described. Two 
of these require special engines, and the other gives the best results 
when used in connection with a special engine. It should not be 
understood, however, that they are the only methods that have been 
used or that no other types of engines or line arrangements have 
been thought of. These methods have been used the most, have 
been given the most publicity, and probably represent the best 
principles so far evolved. The use of overhead logging methods 
for swinging or roading is dealt with under " Swinging." 
UDGERWOOD OVEEHEAD SYSTEM. 
The Lidgerwood overhead system consists of a standing wire 
cable suspended either between two trees, known as the head spar 
and the tail trees— the tree-rigged type (fig. 36)— or between a 
portable steel* head spar and a tail tree— the portable spar type. 
In the tree-rigged type one end of the standing cable passes around 
the tail tree, being held in place by spikes, or over a tree shoe (fig. 
37) suspended on the tail tree, and then down to a stump, to which 
it is made fast. The other end of this cable may be connected to 
