e cars. It is itself mounted
on a flat car.

An improvement on this is the locomotive boom derrick which is widely
used both on the Pacific coast and of late in the Lake Superior
region. It is a combined locomotive, skidder and loader. Its most
unique feature is that it can be lifted off the track so as to allow
flat cars to run underneath it. This feat is accomplished thus: A
device, which is something like that used in elevating the bodies of
coal wagons, lifts the engine several feet above the rails. Then steel
legs, which are curved outwardly, are lowered until the shoes which
are attached to them rest on the outward end of the railroad ties. The
truck of the locomotive is then folded up under it out of the way and
cars can run under it, the curved legs giving plenty of clearance.
The derrick attached is of the breast type, the two legs being firmly
fastened. When anchored the engine can be used either for skidding or
loading. For skidding, there are two cables, one being run out while
the other is being wound on its drum.

[Illustration: Fig. 28. Log Train, Humboldt County, California.]

In loading, the machine is located so that the empty car will be
directly in front of it, and then the logs are lifted up and placed on
the car by the derrick. When the car is loaded the machine can either
move on to the next car, or pull it under itself into place. With the
help of four men it can load from 125,000 to 150,000 feet of timber
in a day. By means of the cable it can make up a train, and then
by lowering the truck and raising the legs out of the way, it is
converted into a locomotive and hauls the train away to the mill or
railway station at the rate of three or four miles at hour.

As forests are cut away along the water courses, railways have to be
resorted to more and more, Fig. 28. This has had a stimulative effect
on the logging business, for now the logger is independent of the
snow. On account of the steep grades and sharp curves often necessary
in logging railways, a geared locomotive is sometimes used, Fig. 29.
It can haul a train of twenty loaded cars up a twelve per cent grade.
The geared engine has also been used as a substitute for cable power,
in "yarding" operations. The "turns" of logs are drawn over the ground
between the rails, being fastened to the rear of the engine by hook
and cable. This has proved to be a very economical use of power and
plant.

[Illustration: Fig. 29. Donkey Engine Yarding