CKOLOGICAL NOTES ON ASSAM. 51 



to the Indus I have heard of no other break in the Sub- Himalayan 



chain. It wouki seem most likely that these deposits on both sides of 



IFpper Assam are continuous round the eastern extremity of the valley. 



' I scarcely like to touch upon the very interesting and important, 



but most intricate, question of alluvium without 

 Alluvium. , . . , -. . . , 



havmg time or data to discuss it as it deserves. 



On first reading Mr. Ferguson's most valuable paper on the Delta of 

 the Ganges,"^ it struck one as prima facie anomalous, and requiring ex- 

 planation, that the deposits of the Bramahpootra should be so backward as 

 compared with those of the Ganges. Its volume is stated as equal to 

 that of the Ganges, and the amount of silt it carries as immensely 

 greater. The valley of Assam above Doobrie is insignificant compared 

 to that of the Ganges above Bajmahal ; over a large portion of it, more- 

 over, rock seems to be near the surface. Yet the alluvial formation of 

 Assam is far more backward than that of the Gangetic plains. Even 

 Supposing that most of the deeper deposits of the Dinagepoor region, and 

 even of the Delta, were the work of the Bramahpootra, the actual 

 relations of the rivers must have been long since established, and still 

 the work of the Bramahpootra, in the Delta, which must to some 

 extent precede that in its valley, is altogether in arrears as compared 

 with that of the Ganges. The temporary diversion into the Sylhet 

 Jheels would hardly be an adequate explanation. The difliculty for 

 which I would seek an explanation is expressed by the question, why 

 is it (remembering the silt-power of the Bramahpootra) that ^'' at present 

 the elevation of the river at Gowhatty, with 350 miles to run, is apparently 

 lower than the Ganges at Rajmahal, within 250 miles of the ocean P^'^f 

 Mr. Ferguson most correctly described Assam as in a " semi-habitable 

 state." From the Bramah Khoond to Doobrie it is under the dominion of 

 the waters. It is in the condition of a Delta without the power of vertical 



* Quarterly Journal Geological Society, Loudon, Vol. XIX., p. 321. 

 t Loc. cit,, p. 330. 



( i37 ) 



