94 MODERN JPORESl' ECONOMY. 



' This may demand some explanation. 



' Many lands are formed of parallel banks, disposed in 

 flat layers and raised up on great inclinations. Often an 

 interposed bed, more soluble or less tenacious, is decom- 

 posed or disintegrated by infiltration. If it happens at 

 the same time that the under banks be attacked by the 

 current at the foot, an enormous weight of ground finds 

 itself suspended over an abyss; the force of adhesion 

 being weakened, it no longer suflSces to keep together 

 this mass and to attach it to the body of the mountain ; 

 it is then detached in a mass, and it slides over the sur&ce 

 of the decomposed bed as on an inclined plane. One may 

 indeed see similiar landslips frequently occurring in the 

 limestones of the lias formation, which decompose with 

 the greatest facility, and which often present a schistos9 

 stratification; this kind of ground extensively prevails 

 here. In other cases the grounds have been formed of 

 the dibris of the upper parts of the mountains ; they 

 compose a rough mass without stratification, and most 

 frequently without consistency, covering the stratified 

 nucleus of the mountain, and forming on its surface beds 

 of great thickness. It rarely happens that a hassin de 

 reception does not contain within its circuit a large strip 

 of this quite recent formation, for it is into the scooped 

 out parts that the M>ris have had to roll and rest. And 

 one may easily see that the erosions which take place in 

 such grounds, when they attack the foundation of very 

 high banks, must force the soil to detach itself in 

 great masses ; and the fractures will take the form of 

 .immense prisms, in accordance with laws similar to those 

 regulating land-shoots {jpousee des terres). So that it is in 

 the abundance of certain kinds of earths, and in the 

 composition of the soil itself, that we find the secret of the 

 principal power of these- torrents.' 



It is established beyond all question that reboisement is 

 an efficient preventitive ; and in manifold cases torrents 

 and landslips have made their appearance after, but only 

 after, the destruction of forests in the basins of reception 



