CAUSE OF EARTHQUAKE. 337 



along the Himalayan mountain-foot, as we know it, is there such excep- 

 tional irregularity, un evenness one might say, in the disposition of 

 these bordering bands of Tertiary strata. 



Coincident with these two inbayings are the two rather similar 

 upland valleys —the Kangra valley and the Pehra Dun — which have 

 come into existence as a joint product of earth movements and rock 

 sculpture. 



We may also notice several other striking facts of structure and 

 Structure of the relief bound up with those just given, facts which 

 Sub-Himalayan zone- although not evident from the sketch map (fig. 46) 

 are well known from other published descriptions and maps. The 

 whole of the Sub-Himalayan Tertiary zone is at a lower general eleva- 

 tion than the older Himalayan tract behind, a feature which obtains 

 throughout the length of the whole range, whilst the valleys also are 

 gentler and the slopes less steep. Furthermore the Sub-Himalayan 

 rocks themselves may be divided up into an older set of harder sand- 

 stones which occupy most of the area including the strip of country 

 next the main boundary fault, and a younger set of softer sandstones 

 and shales overlain by thick beds of coarse conglomerate, which only 

 become specially prominent in the flatter parts of the Kangra valley 

 and Dehra Dun. In each case also these younger sets which dip 

 somewhat gently to the north-east under the Kangra valley and Dehra 

 Dun are suddenly reversed on their N.E. edge and separated from the 

 older sandstones by a reversed fault or faults similar in nature to that 

 of the main boundary fault which in turn separates the latter from the 

 older Himalayan series. 



Such inversions complicated by fold -faults, which characterise the 

 behaviour of the younger to the older series, have been well studied 

 in the case of the Dehra Dun and the other stretches of country between 

 the Ganges and Sarda river. They were so familiar to the author that 

 there was no difficulty in recognising the similarity on a larger scale 

 that the structure of the Kangra valley bore to them ; and it was soon 

 seen that the position of the actual axial centrum, as derived from the 



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