PETROLOGY, 1 9 



The Upper, and a portion of the Middle Sirmurs, are not repre- 

 sented in this district ; we therefore have — 

 r r Upper. 

 \ Siwalik Series . . \ Middle. 

 Sub-Himalayan ) ( Lower (Nahan). 

 System. J 



/ C Middle (Dagshai) in part. 



V Sirmur Series . . [ Lower (Sabdthu . nummu ii t i c ). 



As equivalent terms, I shall make use of the following, which 

 depend for their nomenclature on the character of the composing 



rock : — 



Siwalik conglomerate = U. Siwalik. 



Sand-rock stage «= M. Siwalik. 



Nahan sandstone «= L. Siwalik. 



C M. Sirmur (in part). 

 Nummulitics = ] T Q . - 



( L. birmur. 



It will be seen from this that the geological succession is a simple 

 one. It is even simpler in the de facto Sub-Himalayan zone, as de- 

 fined by Mr. Medlicott ; for, as explained by that author, the num- 

 mulitics lie in a zone among older Himalayan rocks, some distance 

 above the main boundary fault which divides the Sub-Himalayan from 

 the Himalayan country. For several reasons, therefore, I shall only 

 describe in detail the rock series as found occurring actually in the 

 Sub-Himalayan zone. I have been led to do this partly from the fact 

 that the large-scale Forest maps do not, in the majority of cases, extend 

 beyond the Sub-Himalayan zone ; and partly because the nummuli- 

 tics, in this part of the country, are in the form of a very thin band, 

 and appear so constantly in a regular succession upon a set of meso- 

 zoic formations, that it would be absurd to describe the one without 

 the others. The nummulitics will, therefore, be left for subsequent 

 delineation along with the Himalayan formations. This decision 

 will not interfere with my taking any one individual section, such as 

 that along the Pelani R., and discussing it, even as far as the meta- 

 morphic rocks, for the purpose of illustrating the relations of the Sub- 

 Himalayan to the older rocks. Such sections will, however, merely 

 be illustrative, and not exhaustive. 



The description of the individual formations of the Sub-Himalayan 

 tract, from a petrological point of view, is sufficiently easy. There 

 B 2 ( 77 > 



