218 Colonel McMahon — Granite of the Himalayas. 



structural features presented Iby this rock in certain cases were 

 impossible of satisfactory explanation on the supposition of its being 

 a really stratified gneiss." But if the eruptive origin of the gneissose- 

 granite be admitted, the further question arises whether the foliation 

 observed in it was produced prior, or posterior, to the consolidation 

 of the rock. In considering this question, I leave out of sight 

 altogether evidence of fluxion structure as being really irrelevant 

 to the question at issue, though I think it material to state that the 

 rock does show very decided evidence of fluxion. "Without laying 

 any stress on this fact, however, I think the following consider- 

 ations prove that the foliation was not produced by pressure acting 

 on the rock after its consolidation. 



First, the granite is not always foliated at its contact with the 

 rocks into which it has been intruded ; on the contrary, though still 

 porphyritic, it is not unfrequently decidedly gi'anitic along its margin. 

 This fact presents no difficulty to the acceptance of the hypothesis 

 advocated below, but I think it offers an insuperable barrier to the 

 acceptance of the view that the foliation was produced by pressure. 

 Simple pressure will not do : that would not explain the crumpled 

 micas and the very decided evidence of flow or fluxion. Pressure 

 resulting in shear, motion, the development of heat and concomitant 

 chemical and mineral ogical action, might possibly account for the 

 fluxion structure ; but if shear and motion were established on the 

 grand scale required after the consolidation of the rock, the granitic 

 portions along the margins could not possibly have escaped the effects 

 of this action. 



Secondly, the apparently capricious passage from a granitic to a 

 foliated structure in the main mass of the granite is another serious 

 impediment in the way of the acceptance of the theory of dry 

 pressure.^ 



Thirdly, the conjunction of the outer band of gneissose-granite at 

 Dalhousie with the Carboniferous series presents another almost 

 insuperable difficulty. The outer band is the most intensely foliated 

 of all the Dalhousie granite. Parts of it look as if it had been 

 rolled under a gigantic steam roller. Unquestionably it has been 

 subjected to very great pressure, and to either traction, or shearing ; 

 and yet this rock is chock and block with little altered black Car- 

 boniferous rocks. He who would apply the dry-pressure theory 

 to explain the intense foliation of the outer band of granite, would 

 have to invent a new set of conditions out of his inner conscious- 

 ness and bring some other rock into position next the granite before 

 he applied the squeeze. 



Fourthly, the condition of the long tent-peg-like splinter of 

 schist included in the granite, alluded to above, shows conclusively 

 that the granite at the point where the inclusion was found was not 

 subjected to extreme pressure of the character under consideration 

 after its consolidation. Had it been, the splinter of schist would 



^ I use this expression as a short term to indicate pressure applied after the con- 

 solidation of a rock, though, of course, I am aware that pressure so applied may- 

 produce heat and even fusion. 



