﻿308 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 25, 



shells having been obtained from them ; but I think on the whole that 

 the probabilities appear to be in favour of this plain having been a 

 true sea-bottom rather than of having been occupied by a detached 

 body of fresh water. The general extension of some of the older 

 fossiliferous rocks along the northern face of the Himalaya, over a 

 great longitudinal distance, is a fact of which we have tolerable proof, 

 and it thence follows that the line on which they occur, distant about 

 twenty or thirty miles to the north of the great line of peaks, has 

 probably been a sea-margin from the remotest ages of the earth's 

 history until as late as the Oolitic period at least. So far, therefore, 

 there is nothing adverse to my supposition. Nor is the present in- 

 terruption of the plain any proof that it did not once have a far 

 greater extension. This is sufficiently proved by my having traced 

 these Tertiary beds to the very top of the water-shed-ridge in the 

 vicinity of the Niti Pass, where they reach an elevation of upwards of 

 1 7,000 feet ; the summit of that Pass being strewn with boulders that 

 appear to be derived from the white quartzite capping the Silurian 

 strata of the neighbourhood. Further, two or three miles to the 

 south of the Pass, a detached portion of this deposit is to be seen on 

 the declivity of the mountain, which must have been separated from 

 the general mass by the dislocations that have upheaved the whole 

 country. 



It is moreover to be noticed that there seem to be grounds for 

 supposing that plains, such as I have mentioned, are found in other 

 parts of the chain under somewhat similar circumstances, which may 

 not improbably have once formed portions of the same sea-bottom. 

 The plain of Pamir so long known from the accounts of Marco Polo, 

 and the existence of which is fully corroborated by Lieut. Wood, of 

 the Indian Navy, in his Narrative of his Journey to the Source of 

 the Oxus, may be its representative to the west ; while to the east 

 the plains described by Turner as having been passed over during 

 his embassy into Tibet, as well as others mentioned by Kirkpatrick 

 as existing to the north of Nepal, the descriptions of which are quite 

 confirmed by Dr. Hooker, are not improbably of a similar nature. 



Another argument in favour of the marine origin of this deposit is, 

 I think, also to be derived from the very regular way in which the 

 beds of gravel and boulders are laid out, for which I should conceive 

 that some action like that of the tides would be requisite. 



I have already mentioned the occurrence of eruptive rocks in the 

 Tibetan plateau. A great outburst, in which are found hypersthene 

 and bronzite, besides syenitic and ordinary greenstones, and various va- 

 rieties of porphyry, occurs in the vicinity of the lakes which are found 

 at the eastern extremity of the plateau (see Map). The greenstone is 

 known to extend considerably to the west, and forms, at an elevation 

 of about 17,600 feet, the summit of Balch, one of the Himalayan 

 Passes into Tibet which I have crossed (see Sections No. 1 and 2). 



Having thus given a general description of the geology of this 

 region, I shall as shortly as possible enumerate the chief conclusions to 

 which I have been led with regard to the physical forces that have 

 been called into action in the formation of these mountains. 



