170 SUB-HIMALAYAN ROCKS OF N. W. INDIA. [ClIAP. VI, 



their enormous accumulation give evidence of the vast denudation 

 to which the older Himalayan rocks have been subjected, so the 

 disturbance of these strata gives more positive evidence of a period 

 of decadence of the Himalaya. I can see no explanation of these 

 contortions but in the thrust from the mountain mass consequent on 

 the sinking of that mass. Should this conjecture be well founded, we 

 have an example in the straight lines of flexure and of fracture of the 

 Sub-Himalayan rocks between the Sutlej and the Beas of how accurately 

 such testimony can be in accordance with the primary features of a 

 mountain range and those which appear to be necessarily connected with 

 its growth. It would be in agreement with the same opinion to suppose 

 some or all of the general upheaval, which this outer zone has under- 

 gone (independent of that due to contortion), to be an effect of the same 

 cause — the tendency to establish an equilibrium of pressure. 



If once these views have been admitted, it is manifestly difficult to 



draw the line between the secondary and the 

 Difficulty of drawing a 

 line between the rocks primary contortions. All contortions are neces- 

 affected by the two 



systems of disturbance sarily the result of lateral force. In the case 

 respectively. 



we have just described, the force is altogether 



external, and the contortions might be called secondary. When the 



force is exerted within the mass acted on, as in a mass compressed by 



its own gravitating tendency, the resulting contortions might be called 



primary ; they would perhaps be more regular than in the other case. 



The flexures in the old Himalayan rocks may be of this kind. From 



this point of view there are many reasons for associating the calcareo- 



shaly band, which I have described as the Krol-group, with the younger 



rather than with the older strata. Its contact 

 To which system 

 should the Krol-group with the latter is almost always abrupt, and, in 

 of rocks belong. 



many cases, as that described in the valley of the 



Sutlej, the junction is more easily explained by supposing it to be, 

 as in the case of the sub-Himalayan rocks, an original boundary only 



