TOEBENTS OF THE HIGH ALPS. 21 



whioli they have been lost for ever ; in view of this next in importance ia 

 reckoned the ravages committed by the flood in undermining enclosing 

 banks, and thus bringing down fields and houses to be washed away and 

 added to the deposit of debris ; and M. SureU, after having traced the evil 

 to its source, returns to treat of the several parts of the torrent in what 

 would probably be considered by some of my readers an inverted order, — 

 treating first of this bed of deposit, next of the channel, next of the basin 

 drained, and next of the flood creating the torrent. I find it more 

 convenient for my purpose to reverse somewhat the order in which I bring 

 forward his views, following that which I have adopted in enumerating 

 these difierent parts of the torrent. 



Looking at a bed of deposit, or lit de dejection, such as is often seen in 

 the Alps, the question suggests itself, — Whence has come this detritus 1 

 Deep as may be the channel of the torrent, the canal d'dcoulement, this alona 

 could not have suppUed such a mass of material as is generally found con- 

 stituting a lit de dejection. 



A study of the outline aud soil of the bassin de reception, or basin drained 

 by the torrent, with the information previously obtained, supplies the 

 information desired. This is generally more or less of a funnel-shaped 

 basin ; the angle of inclination formed by its sides may be acute, very acute, 

 or it may be obtuse, very obtuse, — -but the resemblance to the sides of a 

 funnel is marked ; the curve may be more or less irreg-ular, and the arc 

 may be more or less nearly complete, but there it is, more or less distinctly 

 perceptible. Here we have discovered what may have been both cause and 

 efiect of what we have seen, — an effect of the rapid rush of water, a cause 

 of the increased fall, and of the increased flow, and increased velocity of 

 flow, and thus of the increased ravages and increased deposit and devasta- 

 tion occasioned by the torrent ; and here we have found what may have been 

 the quarry whence most of the material deposited at the outlet of the gorge 

 may have been obtained. 



It is optional with any one to prosecute the enquiry thus suggested by 

 himself alone, or to do so with the help of others who have gone over the 

 ground before him. It is a matter to which SureU has given careful considera- 

 tion. He has given as the result of his observations and thoughts that in 

 order to the formation of these deposits there must have been in operation 

 a great erosive force, acting on ground susceptible of erosion ; and seeing 

 these meet in the flow of the torrent of water, and in the character of the 

 soil over which it flows, he attributes all the phenomena to the meeting of 

 a copious rainfall and a friable soil, so situated that a rapid flow of the 

 water and a consequent erosion of soil must follow ; and I have cited in 

 detail his exposition of the whole contour of the region being attributable 

 to some such aqueous operation. 



To follow him in his application to bassins de reception of the law thua 

 evolved, it may be desirable to bear in mind that he speaks of three distinct 

 forms of torrents, designated respectively torrents of the first, second, and 

 third classes. The distinction is based entirely upon the position which 

 their bassins de reception occupy in the mountains, — the first proceeding from 

 a col or neck in the mountain range, the second from the mountain brow, the 

 third from the mountain flank, — this difference of position to a great extent 

 determining the differences seen in the aspect they present. 



In torrents of the first kind, in which everything appears on the largest 



