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. 
Rocks 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 spring 
and seepage water oozes out, which keeps the surface moist and slp- 
pery, or else when frozen gives no chance for the snow to le. 
On arocky 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 without 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, ete., are of such influence that the angie 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 ;. itis therefore dangerous in places lia- 
able to 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 artiti- 
ial 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 tothe 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 slides are less frequent the winter after the grass is cut. 
Low shrubs and tree-forms offer a better support to the snow, unless 
their stems are, as 1n 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 destroyed this 
protector, many dangers of a mountain home would be avoided. The 
importance of the forest in this respect was recognized i the Alps cen- 
turies ago, and wherever “ban” forests were maintained, immunity from 
avalanckes 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 fight which | 





















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