27 



The Khishna is the next river 800 miles in length with 

 a drainage area of 94,500 miles. 



The excessive rainfall in the basins of the Brahmaputra, 

 Ganges, and Godavery, and the constant erosion of the banks and 

 beds of those rivers, leads to the formation of that river mouth 

 formation called Deltaic which is observable in other parts of the 

 world where there are large rivers, as for instance, the Nile and 

 Mississippi. 



At the mouth of a Deltaic river and for some distance inland, 

 the river bed is raised by gradual deposits of silt, and if the river 

 is very highly charged with silt the formation of land from the 

 original coast line sea-wards, continually goes on, thus a very 

 important addition to, or alteration of, the features of the country 

 is brought about by rainfall. 



In Bengal a length of about 200 miles of coast consists of 

 estuaries of the Ganges intersected by low islands entirely formed 

 out of river silt. 



The Ganges may be taken to be a typical river possessing the 

 three stages or conditions : first, the Hill stage where it rushes 

 down as a torrent carrying with it large stones and carving out 

 for itself channels in solid lock ; second, the low country stage 

 where seeking the lowest levels it winds along towards its ultimate 

 destination receiving the mud from the drainage of the land it 

 passes through and carrying with it such parts of the detritus 

 which its velocity enables it to carry, dropping the heavier 

 particles, as the fall of the bed flattens, until it reduces itself to 

 a fall of five inches per mile, as between Benares and the delta 

 through which it still further flattens the fall to one inch per mile, 

 which is too fiat to allow the silt to be held in suspension any 

 longer. Here then it enters upon the third stage, and its speed 

 being checked, the river breaks up into innumerable branches, the 

 water spills over the edges and silt is deposited thereon, marshes 

 are formed between the branches and in course of time as more 

 silt is deposited, these marshes are filled up. At the end of the 

 Deltas a network of tidal creeks fiows through the dark and 

 dismal swamps overgrown with Mangrove, Pandanus, and other 

 plants that thrive in brackish water. Here also the ocean currents 

 find themselves checked by the out-flowing streams and they in 

 their turn deposit their sand and thus help in the outward growth 

 of the land. 



It must not be supposed that these deltaic tracts are merely 

 on the immediate coast line ; borings and geological observations 

 have proved that in the case of the Brahmaputra and Ganges the 

 whole of the lower part of Bengal has thus been built up, out of 

 the sea, by means of the river-borne silt. The head of the Delta 



