698 On the Embankments of Rivers. [July, 



the larger embankments beyond the limits of constant change, all risk 

 of having them attacked by the fluctuating stream will be avoided, and 

 regard will merely have to be had to sustaining the pressure of a tran- 

 quil flood or of a given height of water ; while by employing minor 

 embankments likewise, much valuable land may be kept under the 

 plough, except on the occurrence of great floods, which perhaps only 

 take place at intervals of ten, twelve or twenty years. (See PL XVI. 

 sketches I. and II.) 



The upper courses of rivers in Diluvial plains. — In explanation of 

 this scheme it is necessary to recapitulate the distinguishing character- 

 istics of rivers subject to flood and running through diluvial plains. 

 Rivers on quitting the hills rush over the surface of the plains like 

 water spilt upon a table. The channels are shallow, and are at first 

 formed partly by tearing up the soil below, and partly by depositing the 

 coarser materials brought from the hills to the right and left. As 

 banks become formed, the process of deposition is modified into leaving 

 the coarser debritus in the bed of the stream, which is accordingly 

 raised, and the waters being impeded by the diminution of slope, seek 

 a new channel on the original plain to the right or left of that first 

 chosen. In large and constantly flowing streams this process is repeat- 

 ed until at last the general surface of the country is so much raised 

 that the river is eifectually controlled by the mass of its own deposits, 

 and gradually sinks within them, limiting its changes to a series of 

 reflections between two lines, parallel, as in large rivers, at five, eight 

 or ten miles apart. In the case of small, and occasional streams, how- 

 ever, such as the hill torrents between the Ganges and Jumna, such 

 adjustments of channel will never perhaps take place, and these brooks 

 of a rainy day scarcely even now know which of the two rivers to seek, 

 while in the case of others of greater size, as of those descending from 

 the Burdwan and Beerbhoom hills, the settlement is in steady progress, 

 sometimes aided or retarded by artificial " bunds" or embankments. 

 Thus the accompanying sketch No. III. (PI. XVII.) shows the instance 

 of the Bansli Nullah, which joins the Bhagiruttee near Jungypore, and 

 sketch No. IV. shows the instance of the More, which joins the same 

 river between Moorshedabad and Cutwah. The old channels from A to 

 B, toward C, had become so raised with coarse sand, assisted in the case 

 of the More by embankments, that the surface of the country on either 



