PROTECTION AGAINST AVALANCHES. 269 
inclined stratum ot limestone, with a thin layer of calcareous 
marl intervening, which, by long exposure to frost and the 
infiltration ot water, had lost its original consistence, and 
become a loose and slippery mass instead of a cohesive and 
tenacious bed. 
Protection against fall of Pocks and Avalanches by Trees. 
Forests often subserve a valuable purpose in preventing 
the fall ot rocks, by mere mechanical resistance. Trees, as 
well as herbaceous vegetation, grow in the Alps upon declivi¬ 
ties of surprising steepness of inclination, and the traveller sees 
both luxuriant grass and flourishing woods on slopes at which 
the soil, in the dry air of lower regions, would crumble and 
fall by the weight of its own particles. When loose rocks lie 
scattered on the face of these declivities, they are held in place 
by the trunks of the trees, and it is very common to observe a 
stone that weighs hundreds of pounds, perhaps even tons, rest- 
ing against a tree wdiich has stopped its progress just as it was 
beginning to slide down to a lower level. When a forest in 
such a position is cut, these blocks lose their support, and a 
single wet season is enough not only to bare the face of a con¬ 
siderable extent of rock, but to cover with earth and stone 
many acres of fertile soil below.* 
In Switzerland and other snowy and mountainous coun¬ 
tries, forests render a most important service by preventing 
the formation and fall of destructive avalanches, and in many 
parts of the Alps exposed to this catastrophe, the woods are 
protected, though too often ineffectually, by law. No forest, 
indeed, could arrest a large avalanche once in motion, but the 
mechanical resistance afforded by the trees prevents their 
* See in Kohl, Alpenreisen , i, 120, an account of the ruin of fields and 
pastures, and even of the destruction of a broad belt of forest, by the fall 
of rocks in consequence of cutting a few large trees. Cattle are very often 
killed in Switzerland by rock avalanches, and their owners secure them¬ 
selves from loss by insurance against this risk as against damage by fire 
or hail. 
