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Ch. XIX.] 



EISE AND FALL OF THE TIDES. 



477 



storms into a sand-bank, half a mile long, on which a sea- 

 mark was placed. 



Although there is evidence of gain at some points, the 

 general progress of the coast is very slow ; for the tides, 

 when the river water is low, are actively employed in remov- 

 ing alluvial matter. In the Sunderbunds the usual rise and 

 fall of the tides is no more than eight feet, but, on the east 

 side of the del^a, Dr. Hooker observed, in the winter of 1851, 

 a rise of from sixty to eighty feet, producing among the 

 islands at the mouths of the Megna and Fenny Rivers a lofty 

 wave or c bore' as they ascend, and causing the river water to 

 be ponded back, and then to sweep down with great violence 

 when the tide ebbs. The bay for forty miles south of Chitta- 

 o*onp is so fresh that neither algse nor mangroves will grow on 

 it. We may, therefore, conceive how effective may be the 

 current formed by so great a volume of water in dispersing 

 fine mud over a wide area. Its power is sometimes augmented 

 by the agitation of the bay during hurricanes in the month 

 *of May. The new superficial strata consist entirely of fine 

 sand and mud ; such, at least, are the only materials which 

 are exposed to view in regular beds on the banks of the 

 numerous creeks. Neither here nor higher up the Ganges, 

 could Dr. Hooker discover any land or freshwater shells in 

 sections of the banks, which in the plains higher up some- 

 times form cliffs eighty feet in height at low water. In like 

 manner I have elsewhere stated* that I was unable to find 

 any buried shells in the delta or modern river cliffs of the 

 Mississippi. 



The Ganges is always raising the level of its bed and banks 

 in the same manner as the Mississippi before described 

 (p. 443, diagram, fig. 31) ; and we learn from Sir Proby Cantley 

 and Colonel Baker, that even artificial canals constructed for 

 inland navigation in India, such as those of the Jumna, 

 through which the water flows freely, deposit in like manner 

 much of the coarser matter immediately on their banks, so 

 that these last form a miniature representation of those of 

 larger rivers. Mr. J. Fergusson, in his paper on the Delta 



* Second Visit to United States, vol. ii. p, 145 



