Bengal there is a large area of this older alluvium, where the 

 surface is somewhat undulating evidently in consequence of 

 denudation. This tract which is continuous with the newer 

 alluvium of Eastern Bengal, comprises the greater portion of 

 the country to the westward of the Bhagirathi and the 

 Hooghly and owes its comparative elevation to the deposits 

 from the Mourakshi, Ajay and Damodar, brought down 

 from the Rajmehal series of hills i.e., the range of hills in 

 Bengal extending north and south from the Ganges to 

 the neighbourhood of Suri in Bengal and, unlike the other 

 members of the Gondwana system, is confined to the 

 neighbourhood of the eastern margin of the Indian penin- 

 sula. The Rarh country of Bengal and the whole of the 

 Bihar alluvium are Old alluvium, The Old alluvium is under 

 denudation, though occasional elevation by silt formation due 

 to inundation also occurs at times. The New alluvium is 

 ordinarily under formation and it has the tendency to rise, 

 though occasional denudation and disappearance of whole 

 tracts of New alluvium often takes pace in different loca- 

 lities. This general depression of Old alluvium and this 

 general elevation of New alluvium are to be distinguished 

 from the geological upheaval and depression that have taken 

 place in the alluvial tracts of Bengal since the tertiary period. 

 The elevation of the Tippera hill and the coast of Orissa, and 

 the depression of the Gangetic delta by over 481 feet cannot 

 be explained by alluvial action and denudation. There is 

 some evidence to show that the drainage of the Indo-gangetic 

 plain took place at one time by one delta only, viz. t the 

 Delta of the Indus, and that the Gangetic Delta has been 

 formed since the depression of the lower part of Bengal, 

 facilitating drainage by a second delta. The extensive Madhu- 

 pur jungles of Eastern Bengal are probably the remains of 

 the Old alluvium which existed prior to this depression which 

 has resulted in the accumulation of new alluvium in the 

 greater portion of East Bengal. 



