250 



and secured at its ends against other trees, or by posts, or placed upon 

 trestles, if necessary, supported in the middle by posts. Over this tree 

 are placed sticks, with a slight inclination to the mountain side, some- 

 what in the shape of a corduroy bridge, and fastened with wooden 

 nails to the tree and secured by stones on the ground, if possible. 



The retaining- works of stone are the strongest, most lasting, and are 

 possible everywhere, but also the most expensive. For a foundation a 

 space of about 3 feet is leveled, with a slight inclination into the mount- 

 ain side, as if cutting out a road; the base must be natural, not made, 

 soil. The proper making of this foundation-base is of the highest im- 

 portance. The height of the wall must be 3 feet above the ground on 

 the upper side ; the steeper the ground, therefore, the higher necessa- 

 rily becomes the wall work. Simple dry Avails are all that is needed? 

 which, in addition to being cheaper, permit rain and suow water to seep 

 through. 



Especially the ends of the wall must be well secured, and the use of 

 cement in this part of the wall is recommended. The roof is made of 

 large slabs or, in their absence, of sods. 



The length of walls, as of pile rows, depends on the configuration of 

 the soil. The distance of the walls from each other may be greater than 

 with wood-work. 



There have also been used iron rods let into the rock and covered 

 with wood- work. 



The choice of work and the adaptation to the configuration is of 

 greatest imiDortance. 



If the slope presents an even surface, like a roof, the pile rows and 

 walls are placed at intervals, so that the next series covers the even 

 spaces of the one before. 



In ravines, the work is to be placed where the slope changes to the 

 steeper wall. Large bowlders or rocks rising above the surface are often 

 the incipient cause of slides. The safety- work is to be placed at their 

 foot, so, however, that the snow sliding from such elevations should 

 not fall upon the wall, ])ut in front of it, to be there retained. 



Springs and collections of seepage water must be taken care of and 

 properly conducted. 

 A yearly inspection and repairs are, of course, necessary. 

 After the starting-point of avalanches has been thus secured reforest- 

 ation is at once begun, with such species as belong to the locality. 

 The planting is done with seedlings, at a distance of 40 inches, as a 

 rule. This reforestation of the tracks of avalanches, especially in steep 

 situations, including after-planting, is very expensive, and amounts to 

 $25 to $40 per acre in Switzerland. 



In conclusion, it may be stated that the Swiss Government bears 40 

 per cent. — in extraordinary cases 50 per cent. — of the cost of building 

 retaining-works. In reforestation in existing protective forests, 20 to 

 50 per cent., and in planting new forests, 30 to 70 per cent, of the cost is 

 borne by the Government, the commuuilies being liable for the balance. 



