26S MIDDLEMISS: GEOLOGY OF HAZARA AND BLACK MOUNTAIN. 



bable that it was a limit for those beds, their argillaceous and 

 estuarine character bearing out the same view. Hence we must date 

 that boundary fault as having been in the main completed since the 

 Nummulitic limestone was formed, and probably before or just at the 

 beginning of the deposition of the Murree beds. 



The next boundary fault, or line of weakness, between the Slate 



Boundary fault or line and Metamorphic zones, cannot be dated so 

 of weakness between accurately. It must, however, be vouno-er than 



the Slate and Crystal- J S 



line and metamorphic the Infra-Trias, and it most probably went on 

 forming pari passu with the deposition of the 

 Trias, It nowhere shows itself as cutting or truncating any rocks 

 younger than the Trias. 



Thus, each boundary fault is older as we travel north-west across 

 the zones ; and since we must regard them as the great lines of relief 

 which allowed the much folded rocks of each zone to respond to the 

 growing horizontal compression by sliding en masse over the 

 younger deposits which were forming to the south, we have here an 

 argument for the gradual upheaval of the various disturbance zones 

 at successive geological epochs. Thus as regards age we find it 

 true that zone A>B>C>D. 



This practically answers the question propounded above as to 



the cause of the different degrees of upheaval, 



d^°rf to 4K compression, and denudation which mark the 



compression, and denu- disturbance zones ; inasmuch as the different 



dation in each zone. 



effects of the tangential stresses tending to 

 compress the earth's crust laterally, may be most simply understood 

 as due to the different periods of time during which they have been 

 at work : in other words, the older the zone the more it has been 

 elevated, compressed, and denuded. The above hypothesis seems 

 altogether more reasonable than one involving a different local 

 intensity of the tangential forces, an assumption in support of which 

 no arguments can be brought forward drawn from the rocks them- 

 selves, and one which requires a further assumption concerning the 

 direction and origin of those tangential stresses. 

 ( 268 ) 



