134 BULLETIN 711, U. S. DEPARTMENT OF AGRICULTURE. 
obsolescence, also the time the skidder can be used by an operator 
before it has to be disposed of, have a direct bearing on the amount 
that should be written off annually for depreciation. Conserva- 
tively, for the purpose of timber appraisal, the efficient life of a 
skidder should be placed at 10 years, with a scrap value of 10 per 
cent of the original cost. ( See discussion of depreciation on ground 
yarding engines.) 
MACFAELANE SKY-LINE SYSTEM. 
The MacFarlane sky-line system differs from the Lidgerwood sys- 
tem in that no slack-pulling line is employed, the main cable upon 
which the carriage travels being raised or lowered when the system is 
in operation. The first step in the evolution of this system was taken 
in 1905. In that year Mr. C. E. MacFarlane was confronted with the 
problem of moving logs about 900 feet down a steep slope to the 
Kalama River, the elevation of the bench above the river amounting 
to 600 feet, with the slope in places so steep that it was difficult for a 
man to climb up. To move the logs down this slope on the ground was 
not practicable and there was not enough water in the river to permit 
the use of a chute. It was decided that some inexpensive overhead 
method would have to be used. The trip drum of an ordinary 8J b}^ 
10 inch ground yarding engine, set at the top of the slope, was fitted 
with a double brake. A 1-inch plow steel cable was made fast to a 
stump on the opposite side of the river, led up the hill, and passed 
through a block suspended to a properly guyed tree about 60 feet 
from the ground. A J-inch line ran from the main drum, through 
a block attached to the end of the main or overhead cable, and thence 
back around a stump, thus providing a purchase for raising the main 
cable. A five-eighths-inch trip line was strung about 150 feet to one 
side of the overhead cable and led through a block to the carriage. 
In yarding a log, say, 150 feet from the main cable, the trip line 
pulled the carriage and main line over to the log, permitting the log 
to be hooked on ; slack was then taken out of the main cable, thus ele- 
vating the log, by reeling in the J-inch purchase line on the main 
drum, and the log was lowered down the hill by letting out the trip 
line. When the log reached the river the main cable was lowered, 
permitting the load to be unhooked. The device constituted an over- 
head snubbing system, since it relied on gravity to pull the logs in. 
The cost of yarding logs by this system was considerably less than 
it would have been if a ground-yarding method had been used, the 
operator finding that the steep ground was logged as cheaply as some 
moderately level ground with the ground method. The logs ranged 
from 600 to 1,500 feet in volume. 
