Chap. V.] pgst-sivalik deposits. 153 



banks are annually being enlarged by the torrents from the Sivaliks, 

 whereas the regular plains' -deposits are deeply eroded by these same tor- 

 rents in the lower part of their course, and by the great rivers. Whether 

 these more regular strata were laid down in water, in a basin of deposi- 

 tion, after the manner usually supposed, or only by water, by the unaided 

 operation of river action, as has lately been maintained by Mr. Ferguson 

 (Quar. Jour. Geol. Soc, London, Vol. XIX., p. 321), it is evident that long 

 since a period of erosion had set in in these higher regions of the Gan- 

 getic plains. Such being the case, it would be interesting to find out 

 what limits the deposit may have formerly attained. Does that flat talus 

 of coarse debris that is still in process of formation along the base of the 

 Sivalik range rest upon and pass continuously into the topmost beds of 

 the Gangetic formation, or can it overlie a denuded surface of these 

 strata ? I strongly incline to the former supposition. Evidence on the 

 other side is altogether wanting. Had the Gangetic formation ever been 

 much thicker, and thus necessarily extended more or less over the 

 Sivalik hills, the denudation which reduced the level of the main area 

 could scarcely have spared any outlying remnants. Along the south front 

 of the Sivaliks I have not detected any elevated patch of superficial 

 deposits that might not be due to some petty local cause, such as the 

 temporary formation of a lake. About the openings of the great river 

 gorges we sometimes find, close to the Sivalik hills, strata that do not 

 belong to the talus-deposits of these hills. The low flat mounds near 

 Hurdwar are formed by a stratum of stiff clay covering one of coarse 

 boulders, resting on a basis of the highly inclined Sivalik conglomerates, 

 this basis being fully ten feet higher than the present full-flood level of 

 the river. 



In connection with this subject, and especially with reference to the 

 discussion raised by Mr. Ferguson, Dr. Hooker's observations at the base 

 of the Sikkim Himalaya are of great interest. The conditions there are 

 very different from what we have seen to the north-west. In speaking 



U 



