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Page:Popular Science Monthly Volume 19.djvu/851

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often wholly dry, it becomes a flood after a storm, and overcomes all the obstacles that oppose its course. There are clear torrents and muddy torrents. The former, which are the torrents of eruptive regions, carry but little matter with them, and are characterized by sudden freshets, which are due to the fact that the waters running over impermeable rocks, are precipitated immediately into the ravines and collect in considerable masses. The torrents of the second class have formed themselves beds in the loose soil, are continually washing away the bases of their banks, provoking slides, carrying with them solid matters derived from the degradation of the hills, and discharging them in the lower valleys and covering the fields with a thick mud. The bed of the torrent is washed out more and more, and the banks increase at the same time; new ravines are formed, and branches of them, thus eating away the spur of the mountain, which is gradually destroyed, or which, undermined at the base, occasionally slides bodily into the valley, which it closes up.

Attention has long been given to devising means to limit the ravages of these torrents, which ruin the land, threaten estates, destroy roads, and sometimes even compromise the existence of villages. Walls have been built along the banks to protect them, or across the streams to allay the force of the waters. The most efficacious means, however, as yet discovered, has been to maintain the woods on the slopes of the mountain. The effect of cutting away the trees in promoting the formation of torrents has not been doubted by the inhabitants of mountainous regions, and is clearly set forth by M. Surrell, who says: "When we examine the tracts in the midst of which torrents of recent origin have been formed, we perceive that they have in all cases been despoiled of their trees and bushes. If, on the other hand, we examine hills whose sides have been recently stripped of wood, we observe that they are cut up by numerous torrents, which have evidently been formed very lately. Here is a remarkable double fact: wherever there are recent torrents there are no longer forests, and wherever the ground is cleared these torrents are formed; and the same eyes that see the woods fall on the declivity of a mountain, may see appear there immediately a multitude of torrents."

The disastrous consequences of removing the woods from the Alps began to attract attention in the last century, and have since been discussed in many publications and official reports. In 1853 the prefect of the department of the Lower Alps said in a report to the Minister: "If prompt and energetic measures are not taken, it will be almost possible to designate the precise moment when the French Alps will become a desert. The period from 1851 to 1853 will produce a new diminution in the number of the population. In 1862 the Minister will remark a continuous and progressive reduction in the number of hectares devoted to agriculture; each year will aggravate the evil, and in a half-century France will count more ruins and one depart-