CHOKAMB AND KOTR1 DUNS. 83 



stone, the Thakal ga*dh ddnda (42), which appears as a sudden bulging 

 towards the south-west of the normal ridge of Nahans. There is there- 

 fore a manifest dip-fault, or horizontal displacement here, running 

 E.N.E., which is doubtless connected with the slight cross-fault in the 

 Pelani R. at the point where the nummulitics appear. It is owing to 

 this exceptional fault that we have the seldom-seen normal synclin?.! 

 fold, involving an ascending series from north to south. The following 

 seems to have been the chain of cause and effect: — A sigma- flexure 

 with reversed faulting was in the process of forming all along the south 

 edge of the middle band of Nahan rocks. In some places, as in the 

 Ramganga, the thrusting southwards of the Nahans over younger beds 

 has been more prominent than elsewhere. Differential thrusting of 

 this kind might either cause a transverse rupture of the above nature ; 

 or the order of events might be reversed, and a transverse rupture 

 bring about differential thrusting. In this case the rupture seems also 

 to be partly due to the sharp wrench in the general strike of the rocks 

 which becomes north and south as it nears the Kotri N. But, which- 

 ever event came first, the joint resulting position is that, whilst the 

 Nahans on the west side of the rupture have been carried southwards 

 a great distance, the same beds on the east side, being relieved, have 

 simply collapsed into the form of a normal flexure. The strike of the 

 beds, on each side of this horizontal displacement, bends round towards 

 it in the proximity of the line of rupture. Thus, its aspect, viewed on 

 the surface of the ground, is the same as that of a fold-fault viewed 

 in section. The south-westward bulging of the Nahan band west of 

 the horizontal displacement is obviously a return to the position seen 

 in the Ramganga; the amount of the thrusting is about the same; 

 lowermost Nahans appear to be superposed on the top of a thin band 

 of Siwalik conglomerate; whilst all trace of the northern half of the 

 normal synclinal or the middle limb of the sigma-flexure in the sand- 

 rock has vanished. 



On getting to the head of the Sona N., the sand-rock to the south 

 of the line of disturbance is still in force, rising into undulating hil- 

 locks with their triangular wedges very distinctly seen. Away to- 

 F 2 ( 14, ) 



