1867.] the Western Himalaya and Afghan Mountains. 103 



95. The Nummulitic epoch must have been a long one, if we can 

 judge by the thickness of its deposits. There does not appear to have 

 been any violent volcanic action, nor any great and sudden movement 

 during the period, but there was a great deal of very slow and 

 probably imperceptible oscillation. Thus we first find the base of 

 the Nummulitic to be generally a sandstone without fossils,* this 

 is gradually impregnated with calcareous matter, becoming a sandy, 

 very impure limestone, full of shallow water fossils and containing 

 only a few very small species of Nummulites. This has been therefore 

 a period of slow and trifling sinking of the land, and it is probable 

 that the sea never covered it by more than a few feet. Then the 

 oscillation went the other way, and the land appeared again, and was 

 covered by forests. Another slow sinking brought on a fresh incursion 

 of the sea, which soon covered the forests (lignite) with a layer of 

 limestone, full of large Nummulites and other shells. The depth of 

 the sea was greater than before the growth of the forests, but it 

 probably did not much exceed 20 fathoms. Another movement upwards 

 again exposed the land, and again forests grew and formed thin seams 

 of lignite. Again the land sank and the sea covered in the lignite-beds 

 with calcareous mud. At first the depth was trifling, little exceeding 

 20 fathoms, but the sinking continued to the end of the Nummulitic 

 period, and the limestone assumes more and more the appearance of a 

 deep-sea formation as we get higher up the series. It is, however 

 improbable that the volcanic mountains of the great bars of the 

 Himalaya and Afghan mountains were ever covered by the Num- 

 mulitic sea, as no nummulite has ever been found amongst the 

 central chains ;f but that sea filled up the whole of the space between 

 the arms of the great everted V formed by the Himalayan and the 

 Afghan chains, and probably also bathed the outside shores of the arms 

 of the V. This slow, gradual and long continued sinking of the 

 land, during the deposition of the Upper Nummulitic formation, 

 accounts for the appearance of no great depth in rocks which have 



* Sometimes a fragile limestone with Planorhis, and probably fresh- water. 

 See note to para. 66, chap. iii. 



t Dr. T. Thomson reported having observed Nummulitic Limestone in Little 

 Thibet at an elevation of 16,500 feet. But I much doubt the accuracy 

 of the observation, and cannot help imagining that the Thibet nummulites are, 

 like those of Manus Bal, weathered encrinite rings. See "Introduction," 

 page ii. 



