TEANSPOETING POWEE OF WATEE. 267 



pebbles and coarse gravel into the channel of the principal stream. 

 The banks of the other affluents — excepting some of those which 

 dischai-ge their waters into the great lakes — then either retained 

 theh woods, or had been so long clear of them that the torrents 

 had removed most of the disintegrated and loose rock in their 

 upper basins. The valley of the Trebbia had been recently 

 cleared, and all the forces which tend to the degradation and 

 transportation of rock were in full activity.* 



Tra/nsjportvng Power of Water. 



But the geographical effects of the action of torrents are not 

 coniined to erosion of earth and comminution of rock ; for they, 

 and the rivers to which they contribute, transport the debris of 

 the mountains to lower levels and spread them out over the dry 

 land and the bed of the sea, thus forming alluvial deposits, some- 

 times of a beneficial, sometimes of an injurious, character, and of 

 vast extent.f 



A mountain rivulet swollen by rain or melted snow, when it 

 escapes from its usual channel and floods the adjacent fields, 

 naturally deposits pebbles and gravel upon them ; but even at 

 low water, if its course is long enough for its grinding action to 

 have full scope, it transports the sohd material with which it is 

 charged to some larger stream, and there lets it fall in a state of 

 minute division, and at last the spoil of the mountain is used to 

 raise the level of the plains or is carried down to the sea. 



An instance that fell under my own observation, in 1857, will 

 serve to show something of the eroding and transporting power 

 of streams which, in these respects, fall incalculably below the 



* Since the date of Lombardini's observations, many Alpine valleys have 

 been stripped of their woods. It would be interesting to know whether any 

 sensible change has been produced in the character or quantity of the matter 

 transported by the rivers to the Po. — Notice sur les Rivihes de la Lomhardie, 

 Annates des Fonts et Ghaussees, 1847, ler semestre, p. 131. 



•j-Lorentz, in an official report quoted by Marchand, says : "The felling of 

 the woods produces torrents which cover the cultivated soil with pebbles and 

 fragments of rock, and they do not confine their ravages to the vicinity of the 

 mountains, but extend them into the fertile fields of Provence and other de- 

 partments, to the distance of forty or fifty leagues." — Mntwaldung der Gebirge, 

 p. 17. 



