OCT., 1899. 



TIMHERLINE. 



27 



them oil over an almost level tract with such resistless force that the 

 few now left standing arc deeply scarred at a height of 3 to 15 feet 

 above the ground, showing where they were struck by other trees in 

 passing over the deep snow. Hundreds of huge trunks To to 100 feet 

 long and .'> or 4 feet in diameter are strewn in desolate confusion over 

 the broad area tlnit marks the place where this terrific avalanche 

 slowed up and hnally 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. 



Fig. 13. — Track of avalanche iii\ adiuii lll^e^^t nt' Sliasta liis uii Cold Creek, ea.st side of Shasta. 



TIMBERLINE. 



Timbeiiine is the upj)er 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 fir is replaced by the white-bark pine, the latter is the true tim- 

 berline tree and always attains higher elevations than the hemlock. 



Theoretically, nothing is easier than tracing timberline on a moun- 

 tain \vhose upper slopes are bare or dotted with alpine fiowers and 

 whose middle slopes sui)port a continuous forest. Yet on Shasta, and 

 on most high mountains, it is exceedingly difiicult to fix the boundary 

 of timberline or indicate its exact position on a map. Of course, it is 



