part 3] OF THE INDUS, BRAHMAPUTRA, AND GANGES. 155 



Granges, Brahmaputra, and Indus, and never enters the sea. The 

 cetacean inhabiting the Irrawadi, Orcaella brevirostris Owen, is 

 now known to be a marine form which makes its way for long 

 distances up stream, not only in Burma but also in Bengal and 

 Siam. Mr. Oldham noticed that the capture of the Upper Jamna 

 by the Ganges provided a connexion between the Indus and 

 Ganges basins only in the torrential regions unfrequented by 

 such cetaceans ; this difficulty, however, disappears on the assump- 

 tion that, earlier than this, the organic connexion between what 

 are now the Indus and the Ganges was a large continuous river. 

 Dr. Annandale calls attention also to the resemblance between the 

 Chelonia of the two rivers. He says : — 



' Those of the Indus are identical with those of the Ganges, whereas those 

 of the Mahanaddi [for instance] belong, in all cases in which they are 

 probably known, to distinct sub-species or local races. This is particularly 

 noticeable in the case of Trloay.v gcuigeticus Cuyier, one of the commonest 

 and biggest forms in all three rivers. I have been unable to find the slightest 

 difference between specimens from the Ganges and from the Indus ; those 

 from the Mahanaddi (sub-species maJtanadicus Annandale), however, exhibit 

 distinct racial characters, not only in colour but also in the bones of the skull.' 



EXPLANATION OF PLATE X. 



Geological map of the northern portion of the Indian Peninsula, on the scale 

 of 192 miles to the inch, or 1 : 12,165,120. 



Discussion. 



The Pbesldent (Mr. Gr. W. Lampluuh) said that the Society, 

 as well as the Author, was greatly indebted to Mr. Oldham (who 

 had read the paper on the Author's behalf) for the lucid and inter- 

 esting way in which he had dealt with it. liiver-capture had 

 undoubtedly taken place in most parts of the world, and had 

 affected small streams as well as big rivers. The process in a 

 broad way was readily explicable, but it was difficult to understand 

 the final stage, as the gathering-ground of the attacking stream 

 was then reduced to its minimum while the threatened stream 

 maintained its full strength. A temporary blocking of the main 

 stream, or an exceptional Hood, seemed to be required to give the 

 finishing touch. 



Mr. W. Whitakeb asked for information as to the mechanism 

 by which the great reversals of drainage described were brought 

 about. How much was owing to erosion, how much to earth- 

 movement ? 



Dr. J. W. Evans thought that the Author had made out a 

 .strong ease for his contention that in mid-Tertiary times the rivers 

 l n the low ground at the foot of the Himalayas and in the great 

 mid-Himalayan valley flowed towards the' west-north-west, but his 

 contention that the change to present conditions was due mainly to 

 the* working-back of the rivers at their sources was not convincing. 

 Such action was not of great importance among really hard 

 rocks. The variations of relative level due to earth-movements, 



N 12 



