TORRENTS OP THE HIGH ALPS. 33 



abandoned by the torrent from time immemorial. And torrents in all 

 stages of the transition, which begins in the establishment of the extreme 

 limit of the slope, and ends in complete extinction, are met with. Stability 

 begins, generally, first to show itself towards the extremities of the bed, and 

 vegetation establishes itself there, advances, and ends in invading the whole 

 surface of the deposit." Names of several torrents, illustrating what is 

 said, are given. 



These observed facts are followed up by M. SureU with reflections on the 

 age of the torrents themselves. Specifying and detailing the peculiar charac- 

 teristics of three recognised forms of torrents, and generalizing the whole, he 

 concludes, — " The action of torrents may thus be divided into three periods, 

 corresponding to three different ages of growth and development and having 

 each an end to accomplish, and distinct effects which they severally produce. 

 " The first period embraces the creation of the curve or general sweep of 

 the bed of the torrent. 



" In the second period the curve or sweep is detemiined, created, fixed, 

 but the course or channel is not yet fixed ; and it is changed from time to 

 time as if by accident, but all in accordance with law. 



" Finally, the third period is that of a stable regime. The course or 

 channel as well as the curve is permanent, or as permanent as manhood is 

 in comparison with childhood and youth. 



" But many things remain yet to be explained. 



" Why do extinct torrents, when they are confined within banks of their 

 own deposits, plough up the very slopes over which they themselves 

 immediately before flowed without having strength to scoop out of it a bed 

 for themselves 1 The reason is a very simple one. In proportion as the 

 torrent was becoming extinct the waters became more and more limpid. 

 They took then on the same slopes a greater velocity than that which they 

 had when they came charged with alluvial matter, and they then could 

 scoop out where they had previously been depositing. 



" By what cause, again, are new torrents produced ? One cannot at all 

 see why waters which have respected a district during long ages should 

 begin to attack such district now, if all things continue as they were. Those 

 causes which operate to produce a new torrent ought to, have formed it from 

 the first day of the creation of the mountains. How could the district of 

 itself change its form or nature ? 



" It is evident that foreign influences must have interfered, which have 

 modified the primitive conditions. We are thus brought into contact with 

 a new order of facts which demand attention." 



It is then stated that when we examine grounds, in the midst of which 

 are torrents of recent origin, we find them always devoid of trees and of 

 every kind of robust vegetation ; and when, in some other localities, we 

 look to revers, the sides of which have been recently deforested, we see 

 them to be cut by a great many torrents of the third class, which aparently 

 could only have been formed within a few years before ; and extended 

 observations bring under consideration a great many corresponding facts. 



" There exist many revers formed by the detritus of the vertical rocks 

 which generally crown the summits of the mountains. In these mobile soils 

 vegetation takes root with power, and vigorous forests of larch and firs have 

 clothed the sides of the mountains. But the axe, little by little, has deci- 

 mated the trees ; the fellings, made without plan, have opened across the 

 forest large open spaces running with the slope of the r&iers, this arrange- 



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