80 MODERN FOBEST ECONOMY. 



In accordance with this it is mentioned by Mahd : — ' In 

 France, in the Montagne-Noire, experiments have been 

 made in two different valleys, the one wooded, and the 

 other denuded of wood ; and it has been ascertained that 

 the first gives off immediately after rain less water than 

 the second, but on the other hand this becomes rapidly 

 dried up, while the former feeds the stream throughout 

 the entire year. And it has been observed that while in 

 denuded regions the heaviest rains fall in the summer, in 

 wooded districts they fall in the autumn and winter— that 

 is to say, during the season in which, according to Belgrand, 

 they contribute most to feed the water-courses. These 

 observations, made by Maistre in Aude, are of indisputable 

 explicitnessintheir teaching; the results show so evidently 

 that the aridity of a country goes on increasing with the 

 clearing away of woods, and that the water-courses which 

 formerly gave movement to mills have to-day no longer 

 sufficient water to do so. 



' Oauvigril has in like manner observed that a stream, 

 that of Cauman, which takes its rise in a forest district 

 belonging to that same forest of the Montaigne-Noire, 

 formerly gave movement to fulling mills, but after the 

 clearing away of the forest the flow became so irregular 

 that the mills had to stand still through part of the year. 

 The commune, however, having recently replanted the 

 forest, the Cauman has resumed its former regime, and the 

 works go on now without interruption.' 



I have had occasion elsewhere to state that the Alpine 

 torrents are traced by Surell to two sources— the melting 

 of snow about the beginning of June, and storms of rain 

 occurring about the end of summer. The inundations in 

 the Garonne valley was occasioned by similar causes, but by 

 these operating simultaneously, and this in the Cevennes 

 and in the Pyrenees at the same time. In accordance 

 with what has now been stated, when a basin drained by a 

 river is covered by vegetation the flow of the water is 

 retarded, diffused, and protracted ; but when mountains 



