244 



on the dip is less than on the head, when a reverse of favorable condi- 

 tions occurs, but the slides on the head side usually do not fall into 

 places where much damage can be anticipated. 



Eocks easily disintegrated, like the slates, Flysch, etc., are more fa- 

 vorable to the formation of slides than solid rock. 



Very dangerous are steep, stratified rock faces, from which spriug 

 and seepage water oozes out, which keeps the surface moist and slip- 

 pery, or else when frozen gives no chance for the snow to lie. 



On a rocky and very steep mountain side the snow when reaching a 

 certain depth must slide for lack of internal coherence^ especially when 

 dry. During a continual snow-fall several slides may fall from the same 

 place, but they are mostly of small dimensions and little effect. 



If the rock has a soil over it withont vegetation, the formation of 

 slides is dependent in the first place on the degree of steepness. Yet 

 other factors, as the height of the snow, the height of the mountain 

 wall, etc., are of such influence that the angle of elevation may not be 

 made a mathematical expression of the danger. 



If the foot of the snow-wall is washed by a brook, or if a spring or 

 other circumstance disturbs the continuity of the snow-masses, the for- 

 mation of avalanches is favored -, it is therefore dangerous in places lia- 

 ableto avalanches to open a track or even to wade through the snow. 



A declivity which offers varying angles, or is broken by occasional 

 steps or terraces, offers so many points of support to the snow-masses, 

 that avalanches are less liable to occur ; roads, ditches, or other artifi- 

 cial barriers to an even descent, offer also such points of support. 



Most important is the soil-cover. The more and the larger the loose 

 rocks, the more in the line of the horizontal they are placed, the more 

 hold and support has the snow. 



Vegetation has a varying effect upon the formation of slides, accord- 

 ing to the kind of plants that occupy the ground and their size. A 

 grass cover or turf is favorable to the sliding of the snow. It has been 

 observed in the mountain meadows, where the hay is made every sec- 

 ond year, that elides are less frequent the winter after the grass is cut. 



Low shrubs and tree-forms offer a better support to the snow, unless 

 tneir stems are, as m the case of the Mountain Alder, so elastic that after 

 being pressed down they exert a pressure against the snow which tends 

 to interrupt the coherence of the mass, when, with the aid of wind or 

 additional snow-fall, the snow may be set in motion. 



High timber affords the best protection against snow-slides, and if 

 the mountaineer had not in his ignorance removed and destro^^ed this 

 protector, many dangers of a mountain home would be avoided. The 

 importance of the forest in this respect was recognized in the Alps cen- 

 turies ago, and wherever "ban" forests were maintained, immunity from 

 avalanches to the extent of the forest has been secured. An interest- 

 ing account is given of the ban forest of Urseren, which was reserved by 

 the community as early as the year 1397, and of the constant-tight which 



