In the Sierra 



clefts of the rock were broken off near the 

 ground. It seems strange at first sight that 

 :rees that had been allowed to grow for a 

 :entury or more undisturbed should in their 

 >ld age be thus swished away at a stroke. 

 >uch avalanches can only occur under rare 

 :onditions of weather and snowfall. No 

 ioubt on some positions of the mountain 

 lopes the inclination and smoothness of the 

 surface is such that avalanches must occur 

 ;very winter, or even after every heavy snow- 

 torm, and of course no trees or even bushes 

 :an 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 

 [ 291 ] 



