In the Sierra 



clefts of the rock were broken off near the 

 ground. It seems strange at first sight that 

 trees that had been allowed to grow for a 

 century or more undisturbed should in their 

 old age be thus swished away at a stroke. 

 Such avalanches can only occur under rare 

 conditions of weather and snowfall. No 

 doubt on some positions of the mountain 

 slopes the inclination and smoothness of the 

 surface is such that avalanches must occur 

 every winter, or even after every heavy snow- 

 storm, and of course no trees or even bushes 

 can grow in their channels. I noticed a few 

 clean-swept slopes of this kind. The up- 

 rooted trees that had grown in the pathway of 

 what might be called "century avalanches' 

 were piled in windrows, and tucked snugly 

 against the wall-trees of the gaps> heads down- 

 ward, excepting a few that were carried out 

 into the open ground of the meadows, where 

 the heads of the avalanches had stopped. 

 Young pines, mostly the two-leaved and the 

 white-barked, are already springing up in 



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