TIMBER SLIDES AND CHUTES 271 
a support for the slide structure. These may be laid directly on 
the ground or supported on crib work if it is necessary to elevate 
them in order to avoid abrupt changes in grade. Blocks 3 or 4 
feet long with one end beveled at an angle of 45 degrees are sawed 
from crossties, and drift-bolted on top of the sills so that there 
is a space of about 24 inches between the nearest points. Two 
45-pound steel rails, spaced 10 inches center to center, are then 
fastened with railroad spikes to the sills between the side blocks. 
Another rail also is spiked near the top of each sloping face of 
the side blocks. Rail joints are braced with angle bars, properly 
bolted. The advantage of this type of slide is that it can be 
readily moved from one site to another and can be installed by 
the logging railroad steel-laying crew at a daily rate of from 40 
to 60 feet of slide per man. On one operation a slide of this type 
was used to lower logs from the top of a steep grade to a loading 
point along the logging railroad. The logs were brought to the 
slide on wagons, and unloaded on skids which sloped down from 
the upper side towards a set of dead rollers at the head of the 
slide. The logs were pushed forward on the rollers by hand to 
the slide down which they moved by gravity. This type of slide 
is well adapted to moving rough logs since the projecting stubs 
do not catch on the slide. 
GRADES 
The grade is an important feature of all slides. On trailing 
slides the grades are so low that logs will not run by gravity, 
and animal or other power is required to keep them in motion. 
Running slides have a grade which is steep enough to cause the 
logs to move by gravity. 
Slides vary in gradient at different points along the line and 
in some parts they may be trailing slides and in other sections run- 
ing slides. The grade necessary to make logs run by gravity 
depends on the character and condition of the slide, the kind and 
size of the timber and whether the slide is used dry, greased or 
iced. The greater the weight of the log the faster its speed, hence 
large or long logs will run on lower grades than small or short 
ones. Heavy hardwood logs will run on lower grades than 
most softwoods, and peeled logs will nm on lower grades than 
unpeeled ones. 
Earth slides with a 25 per cent grade may be used during the 
