Chap. IV.] nahun and sivalik groups. 101 



Chapter IV. — Sub-Himalayan Series: Nahun and Sivalik 



Groups. 



The rocks of the region, orographically denominated Sab-Himalayan, 

 Nahun and Sivalik P resent great similarity in primary characters, with 



ups " much complexity of structural relations. We can 



trace one tolerably well defined division in these deposits, based upon a 

 general unconformable contact, and hence the distinction of a middle 

 and an upper group, under the names of Nahun and Sivalik. In many 

 sections we shall find evidence of the same kind, suggestive of further 

 sub-division at least locally ; we cannot, however, notice this further than 

 admitting its testimony as to the cotemporaneous action of disturbing 

 and of formative causes. 



Were our notice to be limited to the region east of the Sutlej, it 



Eastern and western might be most convenient to separate the descrip- 

 regions. ^- on Q £ ^ ie ^ w0 U pp er me mbers of the Sub-Hima- 



layan series. Throughout this region it is possible, in almost every 

 section, to draw an exact boundary between the Sivalik and the Nahun 

 groups. Beyond the Sutlej, however, the relation of the two is much 

 obscured: we find, along very definite lines, rocks which we can with 

 certainty pronounce to be the continuation of the Middle rocks ; but inti- 

 mately associated with these, up to the very base of the inner mountains, 

 there occur strata which, as far as I can prove, may be represented 

 among the undoubted Sivalik rocks of the outermost hills. This diffi- 

 culty will be fully illustrated in the sections and the descriptive text ; 

 in the map, however, I prefer adopting the purely arbitrary measure of 

 colouring all the outer rocks west of the Sutlej as Sivalik, to the ambi- 

 guous one of mapping an uncertain and possibly unreal boundary; the 

 innermost band alone is here coloured as belonging to the middle group. 

 It is in narrow bands along the lines of disturbance that the lower rocks 



