262 TOEEENTS EXTINGUISHED. 



desolate valleys in those mountains is to be ascribed to the same 

 cause, and authentic descriptions of the irresistible force of the 

 torrent show that, aided by frost and heat, it is adequate to level 

 Mont Blanc and Monte Kosa themselves, unless new upheavals 

 shall maintain their elevation. 



There are cases where torrents cease their ravages of them- 

 selves, in consequence of some change in the condition of the 

 basin where they originate, or of the face of the mountain at a 

 higher level, while the plain or the sea below remains in substanti- 

 ally the same state as before. If a torrent rises in a small valley 

 containing no great amount of earth and of disintegrated or loose 

 rock, it may, in the course of a certain period, wash out aU the 

 transportable material, and if the valley is then left with sohd 

 walls, it will cease to furnish debris to be carried down by floods. 

 If, in this state of things, a new channel be formed at an eleva- 

 tion above the head of the valley, it may divert a part or even the 

 whole of the rain-water and melted snow which would otherwise 

 have flowed into it, and the once furious torrent now sinks to the 

 rank of a humble and harmless brooklet. "In traversing this de- 

 partment," says Surell, " one often sees, at the outlet of a gorge, 

 a flattened hillock with a fan-shaped outline and regular slopes ; 

 it is the bed of dejection of an ancient torrent. It sometimes re- 

 quires long and careful study to detect the primitive form, masked 

 as it is by groves of trees, by cultivated fields, and often by 

 houses, but, when examined closely, and from different points of 

 view, its characteristic figure manifestly appears, and its true his- 

 tory can not be mistaken. Along the hillock flows a streamlet, 

 issuing from the ravine, and quietly watering the fields. This was 

 originally a torrent, and in the background may be discovered its 

 mountain basin. Such extinguished torrents, if I may use the ex- 

 pression, are numerous." * 



* SunELii, Les Torrents des Sautes Alpes, chap. xxiv. In such cases, the 

 clearing of the ground, which, in consequence of a temporary diversion of the 

 waters or from some other cause, has become rewooded, sometimes renews 

 the ravages of the torrent. Thus, on the left bank of the Durance, a wooded 

 declivity had been formed by the debris brought down by torrents, which had 

 extinguished themselves after having swept off much of the superficial strata 

 of the mountain of Morgon. " All this district was covered with woods, which 

 have now been thinned out and are perishing from day to day ; consequently, 

 the torrents have recommenced their devastations, and if the clearings con- 



