278 DEVASTATIONS AND RESTORATIONS. 



out cavities in its bed, often fills them up again as soon as the diminished 

 velocity of the current allows it to let fall the sand and gravel with which 

 it is charged, so that when the waters return to their usual channel the 

 bottom shows no signs of having been disturbed. In a flood of the 

 Escontay, a tributary of the Ehone, in 1846, piles driven sixteen feet into 

 its gravelly bed for the foundation of a pier were torn up and carried off, 

 and yet, when the river had fallen to low-water mark, the bottom at that 

 point appeared to have been raised higher than it was before the flood, by 

 new deposits of sand'and gravel, while the cut stones of the half-built pier 

 were found hurried to a great depth in the excavation which the water had 

 first washed out. The gravel with which rivers thus restore the level of 

 their beds is principally derived from the crushing of the rocks brought 

 down by the mountain torrents, and the destructive effects of inundations 

 are immensely diminished by this reduction of large stones to minute 

 fragments. If the blocks hurled down from the cliffs were transported 

 unbroken to the channels of large rivers, the mechanical force of their 

 movement would be irresistible. They would overthrow the strongest 

 barriers, spread themselves over a surface as wide as the flow of the waters, 

 and convert the most smiling valleys into scenes of the wildest desolation." 



M. C6zanne refers to the Ardfeche as an illustration of the transition from 

 torrents ta rivers, — it may be described as a torrential river. And he 

 refers to the work by M. de Mardigny as one in every way satisfactory, 

 because the author, free from all foregone conclusions and theories, confines 

 himself to description, provokes neither objection nor opposition. He says, — 

 " The Ard^che is a great torrent, in which everything meets to produce a 

 maximum of effect — a circular basin, converging affluents, denuded moun- 

 tains, extraordinary rains. It is difficult to form any conception of the 

 violence of the storms of rain which the wind from the south-east, the 

 counter current to the mistral, precipitates on the amphitheatre of the 

 C6vennes. M. Tardy de Montravel has received in his rain-gauge, in one 

 day, 792 millemfetres, about 32 inches, as much as falls in Paris in a year 

 and a half These tremendous rain storms occur only in September or 

 October. 



" The Ardfeche is ordinarily a dry river-course, and the flood descends from 

 the mountains and rushes along faster than a horse can gallop : the washer- 

 women have to flee without thought of gathering up their linen ; the de- 

 livery rises suddenly from to from 7000 to 8000 cubic mfetres, and next 

 day the river is fordable : the deluge has flowed away. 



" Sometimes the flood has been seen to rush across the Rhone presenting 

 the appearance of a barrage, a wear, a broad wall of water, to break on the 

 dike opposite the debouchure, and to spread itself over the plains on the 

 left bank, and sometimes to cover the river with a continuous raft of trees 

 torn from the mountains.. 



" The Ardfeche alone creates in the Rhone at Avignon a sudden rise of 

 more than 5 mtoes, or nearly 17 feet, and in that country the sudden 

 floods in the Rhone are called co-ops de I'Ardeche. 



" If at any time a change of wind to the south-east, after having blown for 

 a long time to the east, were to occur, and such a flood to occur when the 

 Rhone and its affluents on the left bank were in flood, the river would pro- 

 bably exceed by many metres the highest level known to have been reached 

 by its waters. 



" Such a thing might happen, and it has been asked,— What, in such an 



