TOEEENTS, ETC., BY COSTA DB BASTELICA. 123 



" In a perfected forest culture it would be possible, by light works, to 

 enrich the soil by favouring this natural eolmatage on steep lower declivities, 

 and if it be desired to fix voluminous materials, wood is preferable ; but on 

 gentle slopes the turf and herbage, which act on the smaU gravel and the 

 finest sands, secure a eolmatage more complete and more compact. 



" It is a fact, ascertained by experience, that lands so covered are more 

 equably levelled than are wooded lands. 



" One may then draw this consequence — that, in the given cases, even for 

 lands which it is desired to cover with woods, it is often preferable to 

 subject them previously to the treatment of simple enclosures, that they 

 may be subjected to this natural preparation which levels and fertilizes them. 



" When, in consequence of the bad state of the soil, and the too advanced 

 state of the ravine, action of this kind would be too slow to heal over these 

 defep sores, it is necessary to aid them by artificial appliances. It often 

 suffices to put some facines across the ravines, to induce the process of 

 eolmatage, and to give to this great energy. It is impossible on this point to 

 lay down any fixed rule. The principle is this — when it is by its concentra- 

 tion that the water acquires its velocity, and its power of destruction, it is 

 necessary, as much as possible, and at all points, to diminish the velocity 

 by extending the section. 



" Simple enclosure does not produce everywhere a pure gazonnement ; 

 there is required a certain altitude favourable to the turf forming plants of 

 high mountains, and also certain conditions of the soil. In the lower 

 districts of some countries, from the time that a piece of ground is no longer 

 open to flocks and herds, vegetation revives, and all the plants of the 

 locality, the seeds of which have been preserved in the soil, or have been 

 borne thither by the wind, deveiope themselves. These are the lavender, 

 the broom, the fescue grass, and very often forest trees, especially the oak, 

 the seeds of which are very tenacious of vitahty. 



"All this natural vegetation, whatever it may be, is valuable when it 

 acts to restore an impoverished land, and to combat the redoubtable effects 

 of ravines. 



" In conclusion, vegetation, under all its forms, is the most powerful 

 means of the restoration and consolidation of the soil, and through this also 

 the most active and most valuable agent in the extinction of torrents ; but 

 there are certain cases in which the evil has made such fearful progress 

 that nature, left to its own powers, would be powerless to repair it. It is 

 absolutely necessary to come to its aid if we wish to protect the valley 

 effectually, and above all if we wish to do it quickly.'' 



Referring to the use of barrages advocated by Surell, by Scipion 'Gras, 

 and by Philippe Breton, M. Costa discusses the whole theory of such 

 appliances, viewed both as designed for the consolidation of the soil in 

 danger of being washed away, and as designed to retain or collect gravel — 

 the former the purpose for which they were proposed by M. Surell, the 

 latter the purpose for which they are prescribed by MM. Gras and Breton. 

 He discusses both at considerable length, and also the diversion of torrents 

 into new courses, and what combinations of each and of all of them with 

 reboisement and gazonnement were likely to be most efficient in different 

 circumstances ; and in illustration of the success in consolidating ground 

 which had followed proceedings such as he advocates, he cites what had 

 been accomplished in the extinction of the torrent of Saint-Martha, near 



