82 LITERATUEE ON T0EKENT8. 



bulk or gravity, a subject underlying tbe proposal of M. Gras, M. Cdzanne 

 ■jfrites, — " The triage of the matters borne along is very strongly marked in 

 torrents which tend to extinction, or only, if the case be so, to take a rigime 

 of greater constancy. It happens even that the lesser stones, &c., being 

 all borne along, there remain only the larger ; the bed is then furnished 

 with a self-created rockery, which energetically resists erosion, and as a 

 necessary consequence the torrent cannot deepen the channel in which it 

 flows. It is then necessary to give some assistance to the torrent, and the 

 larger blocks are removed and ranged along the bank. The water 

 re-collected between these rude embankments digs away anew. This 

 system is much used in Switzerland. The course to be followed is this : 

 replant with woods these parts of the basin in which this can be done ; and 

 when the torrent shows a tendency to cut a bed in the dejection, facilitate 

 the process by removing the self-formed rockwork of blocks denuded by 

 the triage." 



In 1865 was published Memoire sur les barrages de retenue des graviers 

 dans les gorges des Torrents, by M. Philippi Breton, Ingenieur des ponts et 

 Chaussies. Of this M. Cezanne says, — " This treatise may be justly charac- 

 terized a treatise on torrential geometry ; the author demonstrates in it, 

 with beautiful clearness and distinctness, the principal theories which relate 

 to the transport of gravel, — to the profile or outline of the bed of deposit, — 

 to the different kinds of cones thus formed, the troncature or section of 

 which, and the reproduction of which, are explained by beautiful sketches 

 taken from nature." 



Of the design of the work, M.Breton writes, — "Different questions connected 

 with the establishment of barrages, or barriers, for the retention of gravel, have 

 been raised and discussed. But, notwithstanding all that has been done, it 

 appears to me that ideas in regard to what results are to be expected from 

 these barrages are still vague, varied, and undetermined; there is still a great 

 want of decision in regard to selection of location, to the number of barrages 

 to be employed, to the best or most suitable means of constructing them, 

 and to the duration of their efficiency. After having reflected long on these 

 subjects, I have come to be of opinion that, to preserve a plain from invasion 

 by a torrent which debouches on it, it is necessary to establish, in the first 

 place, a single barrage, situated at the outlet of the gorge, or very near to 

 this ; then a second barrage at some metres [or yards], and not more, above 

 the first, when that one shall cease to be efficacious ; then a third at some 

 mtoes above the second, when this in its turn shall have completed the 

 service it can render ; and so on. Such is the subject of this memoir." 



" From this it appears," says M. Cezanne, " that the proposal of M. Breton 

 is the very opposite of that of M. Scipion Gras, submitted eight years ago ; 

 he speaks not of barriers but slightly raised above the level of the bed, or 

 of silts stretching across expansions in that bed, but of solid massive walls, 

 carried up as high as possible by successive stages into the throat of a 

 gorge, and constructed, not of blocks bound to one another by chains, but 

 of hydraulic masonry of the strongest that can be obtained. 



" Barrages in which wood is employed to meet the want of cohesion in 

 gravel, last (says he) but for a short time,— for the wood, buried half of its 

 bulk in the gravel, often dry and often wet, will quickly rot, as quickly as do 

 the Cabrettes, and more quickly than do the coffers known under the name 

 of arks (arches) in the mountains of Dauphiny and Provence. Barrages 



