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Ch. XIX.] 



BY THE GANGES AND BRAHMAPOOTRA. 



483 



month of January, when it is near its minimum, discharges 

 150,000 cubic feet of water per second at Gwalpara, not 

 many miles above the head of its delta, 

 proportions observed at Ghazepoor at the different 



Taking: 



the 



seasons 



as a guide, tlie probable average discharge of the Brahma- 

 pootra for the whole year may be estimated at about the 

 same as that of the Ganges. Assuming this ; and secondly 

 in order to avoid the risk of exaggeration, that the propor- 

 tion of sediment in their waters is about a third less than 

 Mr. Everest's estimate, the mud borne down to the Bay of 

 Bengal in one year would equal 40,000 millions of cubic 



t 



feet, or between six and seven times as much as that brouo-ht 

 down to Ghazepoor, according to Mr. Everest's calculations 

 in 1831, and five times as much as that conveyed annually 

 by the Mississippi to the Gulf of Mexico. 



Colonel Strachey estimates the annually inundated portion 

 of the delta at 250 miles in length by 80 in breadth, making 

 an area of 20,000 square miles. The space south of this 

 in the bay, where sediment is thrown down, may be 300 

 miles from E. to W. by 150 N. and S., or 45,000 square 

 miles, which, added to the former, gives a surface of 65,000 

 square miles, over which the sediment is spread out by the 

 two rivers. Suppose then the solid matter to amount to 

 400,000 millions of cubic feet per annum, the deposit, he 

 observes, must be continued for forty-five years and three 

 tenths to raise the whole area a height of one foot, or 

 13,600 years to raise it 300 feet j and this, as we have seen, 

 is much less than the thickness of the iluviatile strata 

 actually penetrated (and the bottom not reached) by the 

 auger at Calcutta. 



Nevertheless we can by no means deduce from these data 

 alone, what will be the future rate of advance of the delta, 

 nor even predict whether the land will gain on the sea, or 

 remain stationary. At the end of 13,000 years the bay 

 may be less shallow than now, provided a moderate depres- 

 sion, corresponding to that experienced in part of Greenland 

 tor many centuries shall take place (see page 131). A sub- 

 sidence quite insensible to the inhabitants of Bengal, not 

 exceeding two feet three inches in a century, would be more 



112 



