476 



EDMONSTONE ISLAND. 



[Ch. XIX. 



part of the Bay of Bengal was excessive, or that subsidences 

 have occurred in modern times. The latter conjecture is the 

 less improbable, as the delta near Calcutta has certainly been 

 sinking (as is shown by Artesian borings, see p. 478) , during 

 the period of its formation. Parts of Bengal have also been 

 convulsed in the historical era by earthquakes, and actual 

 subsidences have taken place in the neighbouring coast of 

 Chittagong, while ' the swatch ' lies not far from the volcanic 

 band which connects Sumatra, Barren Island, and Kamree * 

 Mr. Fergusson has suggested that ' the swatch/ in which 

 soundings have been made to the depth of no less than 1,800 

 feet without reaching the bottom, is a channel ' scooped out ' 

 by the force of the tides or one which they have had power to 

 keep clear. In support of this view he observes that the tides 

 of the Hoogly have a rotatory motion ;f but he is unable to 

 confirm this by any exact observations as to their velocity, 

 such as might warrant us in ascribing so extraordinary an 

 effect to their excavating power. To me it seems less difficult 

 to conceive the pre-existence of a submarine valley 2,000 feet' 

 or more deep which may have formed part of the original 

 basin of the Bay of Bengal. Before the two great rivers 

 the Ganges and Brahmapootra reach this deep and central 

 part of the gulf they meet the tidal current, and their speed 

 being checked, they part with their sediment, which has in 

 this way been prevented from filling up ' the swatch/ 



mouth of the Hoo 



■&> 



from 



the delta, a new islet was formed at the beginning of the 

 present century, called Edmonstone Island, on the centre of 

 which a beacon was erected as a landmark in 1817. In 1818 

 the island had become two miles long and half a mile broad, 

 and was covered with vegetation and shrubs. 



Some houses 



were then built upon it, and in 1820 it was used as a pilot 

 station. The severe gale of 1823 divided it into two parts, 

 and so reduced its size as to leave the beacon standing out in 

 the sea, where, after remaining seven years, it was washed 



away 



* 



The islet in 1836 had been converted by successive 



See below, Chaps. XXIII. and the Ganges, Quart. Geol. Journ. vol. xix. 



t Fergusson, Changes in Delta of 



1863. 



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