152 DH. E. H. PASCOE OX THE EAELT HISTOET [toL lxxv, 



Upper Jhilam must have formed a continuous tributary with the 

 Soan, and this river was doubtless responsible for the gravels and 

 alluvial deposits of the Soan valley, since these are rather more 

 considerable than they would be had they been entirely due to the 

 modern Soan. The upper part of this tributary was subsequently 

 captured b} r the Lower Jhilam, and the Soan reduced to what it is 

 at the present day. 



The buckling trough-forming movement still went on during 

 the Eecent period, and enormous masses of sediment, estimated at 

 something between 15,000 and 20,000 feet in thickness, were 

 concentrated in this way in the central parts of the Indobrahm 

 valley ; in the lower waters deposition is thought to have been 

 more diffuse. Across the central Punjab and Bajputana there 

 was perhaps more than one geosyncline produced, and the deposition 

 of sediment much less concentrated and still more widely dispersed. 



While the Punjab rivers were cutting back and seizing the 

 middle waters of the Indobrahm, its upper course was being 

 captured, either by two branches of the same river, or by two 

 separate rivers draining Bengal and flowing southwards into the 

 Bay. One of these was the Jamuna or Bengal part of the 

 Brahmaputra, and the other either a tributary of this river or a 

 separate stream, the Ganges. These rivers present the appearance 

 of having been initiated by the continuation northwards of the 

 broad geosyncline of the Bay of Bengal. There is, in fact, 

 evidence from boreholes that the deltaic area is still an area of 

 depression. This geosyncline, the result of the Shan movement 

 from the east, may even have been perceptible as far north as the 

 barrier of ancient rocks which connected the Bajmahal with the 

 Garo Hills. Perhaps with the assistance of this geosyncline, 

 perhaps with the assistance of faults, both streams cut back 

 through this barrier. The Jamuna captured the whole of the 

 upper part of the Indobrahm from Dhubri upwards, and became 

 the modern Brahmaputra. The Ganges cut back in a west- north- 

 westerly direction, capturing element by element the succeeding 

 portion of the Indobrahm as far as Hardwar, where the Alaknanda 

 was captured, the Jamna at that time being the head-waters of the 

 Ghaggar (see below). The voluminous waters of the Indobrahm 

 having been tapped in this way. the scouring of a broad gap 

 through the barrier was an easy matter, and the sediments derived 

 therefrom were flung by the flood into the Bay to form the 

 enormous delta of the Ganges and Brahmaputra. I have stated a 

 definite case for the sake of clearness — obviously there are equally 

 valid alternatives. It may, for instance, have been a single river 

 which cut through the barrier, beheaded the Indobrahm, and 

 "became the Brahmaputra, the Ganges originating north of the gap 

 as a right-bank tributary and cutting back north-westwards in 

 the way described, the confluence subsequently retreating south- 

 wards through the gap. 



The history of the Jamna may be deduced as follows. The 

 Alaknanda, with perhaps the Bhagirathi, having been captured by 



