Early History of the Indus, Brahmaputra, and Ganges. 667 



March 12th.— Mr. G-. W. Lamplugh, F.R.S., President, 

 in the Chair. 



The following communication was read by Mr. R. D. Oldham, 

 F.R.S., in the absence of the author :— ~ 



' The Early Historv of the Indus, Brahmaputra, and Granges.' 

 By Lieut. Edwin Hall Pascoe, I.A.R.O., M.A., D.Sc., F.G.S., 

 Superintendent, Geological Survey of India. 



The occurrences of marine Nummulitic rocks show that in 

 Eocene times a gulf of the sea extended up the Indus valley and 

 the hill country to the west of it, and eastwards along the southern 

 margin of the Himalayas at least as far as the neighbourhood of 

 Naini Tal. In the Himalayan region the marine deposits are suc- 

 ceeded by a series of red clays with intercalated sandstones and 

 occasionally marine beds, regarded by the author as having been 

 deposited in a series of lagoons. The Upper Tertiary deposits 

 consist of a great series of conglomerates, sandstones, and silts of 

 freshwater origin, which are known to extend along the whole of 

 the southern face of the Himalayas. From these geological indi- 

 cations the author concludes that the first effect of the commence- 

 ment of the Himalayan uplift was the establishment of a great 

 westward -flowing river along the southern face of the range, for 

 which he proposes the name of Indobrahm. The distribution of 

 Tertiary rocks on the northern side of the range suggests that here 

 also a westward-flowing river was formed, which discharged either 

 round the end of the range into the same sea as the Indobrahm, or 

 flowed westwards into the region of Turkestan and the Caspian Sea. 

 The subsequent history of the drainage-system consists of the 

 capture of the upper waters of this river by a tributary of the 

 Indobrahm, a cutting-back along the valley to form the east- 

 ward flowing Tsangpo, now the upper waters of the Brahmaputra, 

 and the capture of the lower reaches in part by the Sutlej and in 

 part by the Attock tributary of the Indobrahm, to form the 

 Himalayan portion of the Indus valley. Meanwhile, on the 

 southern side of the range, some of the tributaries on the eastern 

 side of the Lower Indobrahm had cut back from the Sind region 

 and cut off the original bend near Attock, to form the present 

 plains of the Punjab ; and farther east, a river cutting back along 

 the present line of the Gauge tic delta and lower course of the 

 Ganges and Brahmaputra, had captured the upper waters of the 

 Indobrahm to form the present Brahmaputra. The same system 

 of capture had worked westwards, until the tributaries of the 

 Indobrahm had been successively diverted from a westerly to an 

 easterly drainage up to and including the Jumna river. The 

 author finds proof of the recent date of the separation hot ween 

 the drainage-system of the Indus and that of the Ganges in certain 

 historical evidence, indicating that the Jumna was a tributary of 

 the Indus within the human period; in the occurrence of the same 

 species of freshwater porpoise in the two river-systems and 



