1863.] FERGUSSON DELTA OF THE GANGES. 329 



This is a curious and complicated process, which I shall now try- 

 to make as clear as I can, by describing the phenomena as they have 

 occurred in the valley of the Ganges. 



IT. Physical Changes in the Valley of the Ganges. 



1. Upheaval of the Madoopore Jungle. — Although the principal 

 object of this paper is to describe the phenomena resulting from the 

 deposit of silt by the rivers of Bengal, there is one of a contrary- 

 nature which has had so marked an influence on the river-systems 

 of the delta that it is impossible to pass it over. The circumstance 

 I allude to is the upheaval of a large tract of country known as the 

 Madoopore Jungle, which there is every reason to suppose took 

 place in very recent times. 



This tract extends for about seventy miles due north from the city 

 of Dacca, which is built on its southern extremity. Its greatest 

 width in the centre is about thirty-five miles. On its western face 

 it has a well-defined boundary, and rises in hillocks to a height of 

 about 100 feet from the level of the alluvial plain along its whole 

 length ; in the centre its average height is from 40 to 60 feet above 

 the plain, and it gradually slopes away to the eastward, dipping below 

 the old bed of the Brahmapootra, and losing itself in the Sylhet Jheels. 



The surface of this district is a hard ochreous clay, identical, so 

 far as I can judge, with the strata found below the peat and recent 

 deposits at Calcutta, where it exists at a depth of from 70 to 120 feet 

 below the surface of the soil. 



There is, at all events, no a priori improbability against this up- 

 heaval having occurred in very recent times. An inspection of the 

 map will show that it occurred in the axis of the belt of volcanic 

 action which extends from Narcondam through Barren Island on to 

 Cheduba and Raniree, and thence to Chittagong and Dacca. 



Without going further back than the great earthquake which 

 occurred at Chittagong in April 1762*, I may remind the Society 

 that a large tract of land was then submerged, that other parts were 

 elevated, that two volcanos broke out, and the whole settlement was 

 shattered, and that at Dacca the shocks were so violent that the 

 wave from the river swept off a large number of the inhabitants. 



It was not then, however, that any upheaval took place, nor at 

 any period subsequent to the foundation of that city in the beginning 

 of the seventeenth century by Jehanguire ; for its oldest buildings, 

 though cracked, are not destroyed, as they would have been by such 

 a convulsion. And how long before that time it occurred we can only 

 guess by trying to estimate how long it would take the Brahma- 

 pootra to fill up the Sylhet Jheels to the extent it has done, and by 

 the uncertain light of native traditions, some of which will be alluded 

 to in the sequel. 



As hinted above, there exists to the eastward of the upheaved 

 region a depressed area of about equal extent. For a description of 

 this I cannot do better than refer to Dr. Hooker's ' Himalayan 



* Phil. Trans, vol. liii. p. 251. 



