EIVER EMBANKMENTS. 487 



proportion, and tliese processes would be repeated and repeated 

 indefinitely, had not nature provided a remedy in floods, which 

 sweep out recent deposits, burst the bonds of the river and over- 

 whelm the adjacent country with final desolation, or divert the 

 current into a new channel, destined to become, in its turn, the 

 scene of a similar struggle between man and the waters,* 



But here, as in so many other fields where nature is brought 

 into conflict with man, she first resists his attempts at interference 

 with her operations, then, finding him the stronger, quietly sub- 

 mits to his rule, and ends by contributing her aid to strengthen 

 the walls and shackles by which he essays to confine her. If, by 

 assiduous repair of his dikes, he, for a considerable time, restrains 

 the floods of a river within new bounds, nature, by a series of 

 ingenious compensations, brings the fluctuating bed of the stream 

 to a substantially constant level, and when his ramparts have 

 been, by his toO, raised to a certain height and widened to a cer- 

 tain thickness, she, by her laws of gravitation and cohesion, con- 

 sohdates their material until it becomes almost as hard, as indis- 

 soluble, and as impervious as the rock. 



But though man may press the forces of nature into his ser- 

 vice, there is a limit to the extent of his dominion over them, and 



found that the bed of the Sieve had heen permanently elevated two yards be- 

 tween 1708 and 1844, and that of the Fosso di San Gaudenzio more than a yard 

 and a half between 1752 and 1845. These, Indeed, are not rivers of the rank 

 of the Po ; but neither are they what are technically called torrents or movm- 

 tain streams, whose flow is only an occasional effect of heavy rains or melting 

 snow. — Trattato delle Macchie e Forests di Toscana, Firenze, 1857, p. 29. 



* The Hoang-ho has repeatedly burst its dikes and changed the channel of 

 its lower course, sometimes delivering its waters into the sea to the north, 

 sometimes to the south, of the peninsula of Chan-timg, thus varying its point 

 of discharge by a distance of 220 miles. — Elisee Recltjs, La Terre, 1. 1., p. 

 477. 



See interesting notices of the lower course of the Hoang-ho in Nature, Nov. 

 25, 1869. 



The frequent changes of channel and mouth in the deltas of great rivers are 

 by no means always an effect of diking. The mere accumulation of deposits 

 in the beds of rivers which transport much sediment compels them continually 

 to seek new outlets, and it is only by great effort that art can keep their points 

 of discharge approximately constant. The common delta of the Ganges and 

 the Brahmapootra is in a state of incessant change, and the latter river is said 

 to have shifted its main channel 200 miles to the west since 1785, the revolu- 

 tion having been principally accomplished between 1810 and 1880. 



