Chap. IV.] nahun and sivalik gkoups. 117 



Having indicated the extent of the Nahun band in this region, that 

 „. *,., , of the Sivaliks is also fixed. The same doubt 



bivahk group of east- 

 ern region. applies to both along their boundary in the duns, 



owing to the great difficulty of assigning a limit between the Sivaliks 



and more recent deposits ; the section in the river Noon will illustrate 



this point. On the score of composition there is much more to be said 



of the younger group ; both vertically and horizontally its strata exhibit 



some remarkable variations. It were a deliberate 

 Lithological variations. 



error to seek for general regularity or defmiteness 



in deposits that were so palpably accumulated under local influences, but, 



roughly estimated, there may be four divisions made in the Sivalik 



series where it is most developed, — in the range 

 A general sub-division. 



separating the Behra Dun from the plains, to which 



the name, Sivalik, was originally exclusively applied. The lowest of these 



sub-groups of strata is the least marked, as it is also the least exposed, 



its base being unknown. Its only peculiarity is a greater prevalence of 



clays than in the portion of the series immediately overlying it ; still, 



even here the thick-bedded sandstones predominate. Above this comes 



a thick band of massive sandstone with scarcely a parting of clay, or 



on the other hand, with only an occasional small pebble. Passing 



upwards, strings and beds of pebbles make their appearance, increasing 



into massive banks of conglomerate, but still with a clear sand matrix. 



The change is rather abrupt into the fourth stage of deposits, consisting 



of thick-bedded stiff clays and coarse clay-conglomerates. The crests of 



the passes and of the inner portion of the range are of this top band ; 



it also occupies the area of the dun. It is important, however, to know 



that it is in no degree a dun-formation : this point is strongly suggested 



by the fact, just mentioned, of its forming the inner slopes and crests of 



the Sivalik hills, and with the same steady dip as the rest of the group ; 



but it is put beyond a question by the fact of the re-appearance of these 



same beds at the most south-westerly point of the whole range, to the 



