240 DESTRUCTIVE ACTION OF TOERENTS. 



waters occasioned no otlier evil than to produce, once in ten years 

 upon tlie average, an inundation whicli should destroy the harvest 

 of the low grounds along the rivers, the damage would be too 

 inconsiderable, and of too transitory a character, to warrant the 

 inconveniences and the expense involved in the measures which 

 the most competent judges, in many parts of Europe, believe the 

 respective governments ought to take to obviate it. 



Dest/ructwe Action of Torrents. 



But the great, the irreparable, the appalling mischiefs which 

 have already resulted, and which threaten to ensue on a still more 

 extensive scale hereafter, from too rapid superficial drainage, are 

 of a properly geographical, we may almost say geological, char- 

 acter, and consist primarily in erosion, displacement and trans- 

 portation of the superficial strata, vegetable and mineral — of the 

 integuments, so to speak, with which nature has clothed the skel- 

 eton framework of the globe. It is difficult to convey by de- 

 scription an idea of the desolation of the regions most exposed to 

 the ravages of torrent and of flood ; and the thousands who, in 

 these days of swift travel, are whirled by steam near or even 

 through the theatres of these calamities, have but rare and im- 

 perfect opportunities of observing the destructive causes in ac- 

 tion. Still more rarely can they compare the past with the actual 



meadows in Lincolnshire, whicli have been covered with shme by warping, 

 as it is called, or admitting water over them at high tide, are remarkably pro- 

 ductive. 



Recent analysis is said to have detected in the water of the Nile a quantity 

 of organic matter — derived mainly, no doubt, from the decayed vegetation it 

 bears down from its tropical course — sufficiently large to furnish an important 

 supply of fertilizing ingredients to the soil. 



It is computed that the Durance — a river fed chiefly by torrents of great 

 erosive power — carries down annually solid material enough to cover 272,000 

 acres of soil with a deposit of two-fifths of an inch in thickness, and that this 

 deposit contains, in the combination most favorable to vegetation, more azote 

 than 110,000 tons of guano, and more carbon than 121,000 acres of woodland 

 would assimilate in a year. — Elisee Reclus, La Terre, vol. i., p. 467. On the 

 chemical composition, quantity and value of the solid matter transported by 

 rivers, see Herve Mangon, 8ur VEmploi des Eaux dans les Irrigations, 8vo. 

 Paris, 1869, pp. 133 et seq. Duponchel, Traite d' HydrauUque et de Oeohgie 

 AgricoUs. Parir., 1868, chap, i., xii., and xiii. 



