produce or throw off a sliding mass of snow. 

 Raise, lower, or roughen this slope, increase or 

 decrease the annual snow-fall, or change the 

 direction of the wind, — and thus the position 

 of snow-drifts, — and there will follow cor- 

 responding slide-action. Wind and calm, grav- 

 ity, friction, adhesion, cohesion, geology, tem- 

 perature and precipitation, all have a part and 

 place in snow-piling and in slide-starting. 



The Century slides are the damaging ones. 

 These occur not only at unexpected times but 

 in unexpected places. The Century slide is the 

 deadly one. It usually comes down a course not 

 before traversed by a slide, and sometimes 

 crashes through a forest or a village. It may be 

 produced by a record-breaking snow or by 

 snow-drifts formed in new places by winds from 

 an unusual quarter; but commonly the mass is 

 of material slowly accumulated. This may con- 

 tain the remnant snows and the wreckage spoils 

 of a hundred years or more. Ten thousand 

 snows have added to its slowly growing pile; 

 tons of rock-dust have been swept into it by the 

 winds; gravel has been deposited in it by water; 



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