38 E^suM^ OF sueell's study of 



such basins j and at the same time it should be recollected that the cubical 

 measurement of these is still far from representing all the mass of material 

 which the torrent has drawn away from the mountain, since a portion of 

 this has been swept into the river, which has widely dispersed it far away. 

 By an effort of thought let ua transport the mountain formed by [this 

 deposit to the upper part of the torrent ; let us throw this into the hoUow 

 constituting the basin ; let us add to this all that has been carried away by. 

 the river, and we shall not be far from having fiUed up those deep excava- 

 tions which we hesitated just now to attribute to the digging away of the 

 waters. And we may come in this way to comprehend that there is no ex- 

 aggeration in alleging that the whole valley of the torrent, from its birth to 

 its junction with the thaXtveff, is the work of the waters alone." 



Of the correctness of this view there are numerous corroborative indica- 

 tions or proofs referred to ; and as the result of the whole of these observa- 

 tions the natural history of many of the torrents in the High Alps appears 

 to have been this : a deluge of rain such as is brought by the fcehn, falling 

 on an exposed bare spot of greater or lesser extent on the col, or the summit, 

 or the flank of a mountain, has washed away soil and formed thus a hoUow 

 basin with an outlet on its lower-edge, the water flowing oflf by this has 

 made a little runnel carrying away, along with the earth washed out of the 

 hollow, earth which impeded its progress ; and as more and more fell into 

 the runnel, through the undermining of its tiny banks, carrying this oflf also 

 and depositing the detritus, whenever a reduced inclination of the ground 

 reduced the velocity of the flow, and forming thus and there a tiny bed of 

 deposit. But the operation — ^the process thus begun — ^goes on widening 

 deepening, extending the basin drained, and the gorge or channel, and 

 adding to the deposit, increasing both its depth and extent, till they have 

 each of them attained the fearful aspect they now present. 



But there have been similar torrents in the same region in former times 

 — which are now as innocuous as the extinct volcano — they too, to borrow 

 the term, have become extinct ; and the brushwood and trees growing on 

 the bed of deposit tell by their age that these torrents have been extinct 

 long. And while the lits de d&jection are now covered with vegetation, and 

 in some cases with fields, and houses, and towns, the basin and the gorge 

 have also been covered with forests. May not this have been the cause of 

 the extinction i The more closely and the more extensively the subject is 

 studied the more manifest does it appear that it must be so. Thus may it 

 have been in the olden time. In more modem times the destruction of 

 trees has preceded the formation of torrents ; and the spread of the forests 

 seems to have preceded the extinction of those of an older creation. This 

 is in accordance with everything that is known in regard to the action of 

 trees in promoting the infiltration, retention, and percolation of water 

 ^through the soil, and subsoil, on which they grow. 



With the light thus obtained, we are enabled to trace back the natural 

 history of the existing torrents to the destruction of herbage and trees 

 formerly growing on the bare and exposed spots, from which these torrents 

 have originated, — a destruction of which in some cases historical records 

 direct us to the time in which it occurred ; while in other cases it has 

 occurred within the memory of the present inhabitants of the district. 



The student of physical phenomena may meet occaBionally with what 



