64 MIDDLEM1SS: PHYSICAL GEOLOGY OF SUB-HIMALAYA. 



dip of 50° S.S.E. gradually increases up to 90 , and then becomes 

 inverted 40 in the opposite direction at the position of the fault 

 (see section VI). North of the reversed fault, lowermost Nahan 

 sandstones, with a great display of purple shales, and much crush- 

 ed, dip north at high angles. It is of the utmost importance to 

 get a right conception of the relation of the three rock stages to 

 one another in this locality. If we examine the horizontal sec- 

 tion (No. VI) we shall see that, for the sake of simplicity, the south- 

 ernmost fault may be neglected. What we have to consider is 

 the reversed fault separating the Siwalik conglomerate from the Na- 

 hans. It is apparent at a glance that this Nahan-Siwalik boundary is 

 not the simple thing we saw it to be south of the Sanguri sot, re- 

 presented in section V. In the latter section there are to the north 

 of the fault uppermost Siwalik conglomerates lying in marked uncon- 

 formability upon lowermost Nahans ; from which the inference was 

 drawn that the lower part of the conglomerate, and the whole of the 

 sand-rock stage, had been overlapped as if deposited against a 

 shelving slope of Nahans. That is to say, the position of the fault had 

 to be regarded as a limit of deposition for the Middle and most of the 

 Upper Siwalik stages. The case in the present section, however, is 

 different. From the fact that to the north of the reversed fault, the 

 Nahans are again covered conformably by the sand-rock at Gutua 

 g£dh, we cannot regard the fault as a limit of deposition for that rock 

 stage. It must have once spread over the high Nahan ridge, con- 

 tinuously, from what is now the west end of the Pcitli dun into con- 

 nection with the corresponding rock higher up in the Pelini R. Of 

 course we might assume that the Nahan ridge was a ridge in part 

 when the sand-rock was deposited, and that the latter was laid down 

 synchronously on each side of it ; but this would be a gratuitous as- 

 sumption, and not borne out by sections across the same ridge fur- 

 ther north-west. If we look at section VII across the Sona N. near 

 Dhansi chaor, we find no signs of the sand-rock thinning out or over- 

 lapping itself against a cliff of Nahan sandstone ; on the contrary, 

 the northern half of the inverted synclinal (which at the same time is 

 ( 122 ) 



