PREVENTION OF TORRENTS AMONG THE ALPS. 357 



When stone cannot be had, they build these barriers of timbers and 

 fascines, but these can never be of much size, nor are they very dura- 

 ble. They are only used in case of little injuries which vegetation will 

 easilj' cover. 



Ihile-paths. — While building the partial dams they open within the 

 limits of the work such paths as are necessary. These are about a 

 meter wide and have an easy grade, so as to easily pass back and forth 

 in supplying the works. These paths also are quite essential to the 

 dams and facilitate the distribution of labor. Being destined at a 

 future day for use as roads for removing the growth of wood, they 

 ought, as much as possible, to be made with reference to this use. 



Sustaining-walls. — In passing each ravine the mule-paths are sus- 

 tained by dry stone walls or by the dams, according to the extent of 

 the ravines. 



Drains. — In the lateral ravines the simplest, cheapest, and most 

 effectual method of arresting the process of degradation is by means of 

 drainage. These drains are made by throwing into the bottom of the 

 ravines whole trees, with the heads downward, together with fascines 

 and branches, and then with powder throwing down the impending 

 banks of earth, which, falling naturally into the lowest part, are 

 crushed to pieces in falling. They thus obtain at once, along the 

 whole length of the ravine, a large mass of loose earth, which raises the 

 beds of the channel, sensibly reduces the stee'pness, and secures a deep, 

 damp, and finely-pulverized soil, upou which, from the first year, they 

 may establish a good vegetation. 



When the bottom is solid, narrow, and very steep, it iS necessary, in 

 order to prevent sliding, to build redans in some places, and to make 

 small dams, and for these purposes they employ conical gabions, with 

 the open end above. These drains, even in the driest places, often col- 

 lect water enough to form little springs through the summer. 



Belts. — After the banks have become thus consolidated, the portions 

 denuded and destined to be covered with vegetation are divided into 

 horizontal belts, as also the zones affording pasturage, when superficial 

 erosions are to be feared. These belts, the width of which is from 0.8 

 to 1.0 meter, are nearer together where the slope is steeper (being on 

 the average 4 meters apart), but must not be too near each other, as 

 they are then liable to slide. Being sufficiently sloping in toward the 

 mountain, they arrest the water that falls, and force it to soak into 

 the ground. They spade into the slope 0.4 to 0.5 meters deep, as much 

 as possible the year before planting, so that the soil shall have time to 

 harden by the action of the atmosphere, and to be comminuted by the 

 frost. 



PacTcing with clay and brush. — In very steep places the belts are sus- 

 tained by the aid of a packing of clay and brush, or by dry stone walls. 

 These packings and made with strong stakes, above which are fascines 

 dipped in mud and packed with soil. These fascines by their slow decay 

 serve to fertilize the soil, and to favor vegetation. 



Coverings. — When the surface between the belts is easily degraded, 

 or keeps its place badly, the parts most liable to this accident aie 

 covered with brush laid imbricating, rather thick, and top downward. 

 They are also covered with all kinds of rubbish, in places most liable to 

 erosion. These coverings, even without fastenings, retain the soil per- 

 fectly and protect it from the rains, by which they deaden their force. 

 They retain the moisture of the soil, and hinder evaporation. 



In the zones affording pasturage, the opening of belts, with sustaining- 



