ocr., 1899.) TIMBERLINE. 27 
them on over an almost level tract with such resistless force that the 
few now left standing are deeply scarred at a height of 10 to 15 feet 
above the ground, showing where they were struck by other trees in 
passing over the deep snow. IJlundreds of luge trunks 75 to 100 feet 
long and 3 or 4 feet in diameter are strewn in Aesolate confusion over 
the broad area that marks the place where this terrific avalanche 
slowed up and finally stopped. The accompanying illustration shows 
a part of this area, and also the gate cut by the avalanche when it 
struck the upper edge of the forest. 
Sehe otieaate.| 
TIMBERLINE, 
Timberline is the upper or boreal limit of tree growth, as determined 
by temperature. It varies somewhat according to the particular species 
of tree, for even Hudsonian species differ in the degree of cold they 
are able to endure. Thus in the northern Cascades where the alpine 
hemlock and alpine fir are the dominant timberline trees, the fir pushes 
up to higher altitudes than the hemlock. So on Shasta, where the 
alpine tir is replaced by the white-bark pine, the latter is the true um- 
berline tree and always attains higher elevations than the hemlock. 
Theoretically, nothing is easier than tracing timberline on a moun- 
tain whose upper slopes are bare or dotted with alpine flowers and 
whose middle slopes support a continuous forest. Yet on Shasta, and 
on most high mountains, it is exceedingly difficult to fix the boundary 
of timberline or indicate its exact position on a map. Of course, it is 
