jS M1DDL.EMISS: PHYSICAL GEOLOGY OF SUB-HIMALAYA, 



Massive limestone (4). 

 Nahans (7). 



Middle Siwalik sand-rock (8). 

 Nahans (7). 



Siwalik conglomerate (9). 

 Middle Siwalik sand-rock (8). 

 Nahans (7). 



s.s.w. 



In all there are twelve stratigraphical zones, grouped into six dis- 

 turbance zones. 



Fourthly, each disturbance zone, except the purple slate and 

 volcanic breccia, has its ascending order of rock stages at the surface 

 from south to north ; nowhere is there an ascending series of different 

 stages dipping south ; for such a position in this greatly crushed 

 region is unstable. As soon as formed, it would tend to become 

 vertical and then inversed by the ceaseless horizontal crush of the 

 rocks ; and then following on inversion would come the tearing along 

 it (now become the middle limb of a sigma-flexure), and the final 

 condition of a reversed fault. As a corollary to this, every formation, 

 when its southern neighbour is younger than itself, is divided from it 

 by a reversed fault ; and, when its southern neighbour is older than 

 itself, it is in normal superposition upon it. Only among the younger 

 Siwaliks do we see, in an individual stratum, a normal dip to the 

 south still left as evincing portions of a middle limb not entirely in- 

 verted or disseminated. 



Fifthly, each disturbance zone is, considering the average age of 

 its rock stages, older than the succeeding zone to the south ; because 

 each succeeding zone introduces a newer member than was previ- 

 ously present ; this is shown in the table above by the numbered 

 formations, a higher number and a higher average number coming in 

 with each disturbance zone to the south. Should the present plainward 

 edge of the hills be a reversed fault, it will in due order come to pass 

 (when a further crushing of the margin of the hills has taken place) 



( 136 ) 



