TITLES OP TBEATISES. ' 129 



violent, now feeble, this shotild be rectified! by the extensive application' of 

 works of consolidation, such as Surell has recommended. 



" The works of reboisement and gazonnement, to be effectual, require to be 

 extended over large areas. Work's of artificial consolidation, on the contrary, 

 may be confined Within a limited space, and the evil may in some cases be 

 stifled by attacking it in its principal source. 



"Sometimes it may happen that, through the pastoral and agricultural 

 operations carried on, it is impracticable' to' give to hoisemewt'the whole 

 ejrtension necessary to meet the evil. Every case must be decided on its own 

 merits. And-, from the general considerations adduced, it is apparent that it is 

 impossible to lay down invariable rules' of procedure applicable to every case. 



" When there is no special urgency for securing immediate restdts, it is 

 preferable to employ at once vegetation. ' By enclosing a Space, it is found 

 that the spontaneous work of nature exercises a most favourable inflU'ence 

 on the soil. Cover, then, with woods aU the lower slopes, where there is 

 no fear of the earth crumbling away, and where the spontaneous work of 

 nature is not likely to cover them with vegetation. With this done, the 

 delivery of water will insensibly diminish ; losing bulk and velocity, it 

 retains no longer the same power of undermining and Washing away ; the 

 hills are less frequently and less powerfally attacked ; ahd where it is 

 reckoned that the torrent is sufficiently enfeebled, there may then, if it be 

 thought necessary, be established in the gorges, with greater ease and at 

 less expense, works of consolidation deemed useful. 



" This order of procedure is more sure, and more economical, but more 

 slow than is the reverse. 



" With the vegetation there may be combined, on the upper slopes and 

 in the lesser ravines, a great many small works of consolidation, the design 

 of which is to efiect this by retarding the velocity of the flow, and the stib- 

 stituting oicolmatage for the undermining and carrying away of the soil. 



" The time for undertaking works of consolidation in the gorges must be 

 determined by the degree of urgency for a speedy extinction of the torrents, 

 and by administrative considerations, of which the superior authcffity' is 

 the judge." 



In illustration of what may be done, M. Costa cites the extinction of the 

 torrent of Saint Martha, already referred to. 



Besides the works which have been cited, the following have been 

 published in France : — 



Belgband, membre de I'lnstitut, inspecteur g6n6ral des ponrts et chauss6es. 



Hydrologie et mitiorologie du hasdn de la Seine. 

 Bblancbe, ing^nieur en chef des ponts et chauss6es. Essai sur le mowie- 



ment permanent des eaux courantes. 

 CoLLiGNON, cours d'hydraulique profess6 k I'Ecole des ponts et chauss6es. 

 CoMOT, inspect. g6n. des ponts et chauss6es. MSmoires sur les cmvrages 



de defense contre les inondations. 

 Daeot et Bazin. Eecherches hydrauUques. Premifere Partie — Eech^rches 



exp6rimentales sur I'^coulement de I'eau dans les canaux d6couverts. 



Deuxifeme Partie — Eecherches exp6rimentales sur la propagation 



des ondes. 

 DuMONT, ing^nieur en chef des ponts et chauss6es. Les eaux de Lyon et 



de Paris, — projets, traces et details d'ex6cution suivis d'une pi:atique 



des distributions d'eau. 



O 



