J58 SUB-HIMALAYAN ROCKS OF N. W. INDIA. [CHAP. V. 



at the earth's surface. One phase of their geological function has 

 lately been ably treated in a paper, already mentioned, on the Ganges 

 delta, by Mr. Ferguson ; the author chiefly illustrates the action of rivers 

 as agents of rock-formation, and, as contingent upon that process, he 

 exhibits the mutability of rivers themselves. The antiquity of rivers,, 

 and their powers as agents of destruction might form the subject of an 

 essay as instructive as Mr. Ferguson's, based upon a study of the Ganges 

 and its great associates in the Himalayan mountains. It has hitherto 

 been the fashion* to attribute the deep valleys, or rather gorges of the 

 Himalayas, in a great measure to marine denudation, likening them to 

 the deep fiords of the Norway coast. The simile reversed may be just 

 as much to the point, — the Norway coast or any other such (I too speak 

 without reference to details,) may be likened to a submerged mountain 

 range. I feel assured that these valleys can all be more justly accounted 

 for by river-action and atmospheric denudation generally, operating 

 through the untold ages of the Sub-Himalayan epoch. Every reader 

 of this memoir will be familiar with descriptions more graphic than I 

 could give, and with sketches of the deep gorges of the Himalayas. I 

 only add one view to the number already published. Plate III. exhibits 

 a view of the gorge of the Tonse where crossed by the Simla and Masuri 

 road, at the Tiuni bridge, a rude suspension bridge of native con- 

 trivance ; at a considerable elevation over the stream glacial blocks 

 are seen on the steep slopes. 



The Eavee in its bend round the termination of the Dhaoladhar gives 

 a good instance of a river course adapting itself to the conditions of rock- 

 structure. At innumerable places on every river and stream we may 

 find instances of the deliberate contravention of this apparently necessary 

 law of natural selection as applied to river courses, and which breaches 

 of law may safely lead us to infer very remote conditions of the surface, 



* Dr. Thomson, " Western Himalaya and Tibet, 1 ' p. 27 ; Dr. Hooker, "Himalayan Jour- 

 nals," Vol. I., p. 380 ; and R. Strachey, Quar. Jonr. Geol. Soc., London, Vol. VII., p. 309. 



