346 Lieut.- General C. A. McMahon — 



of the rock by pressure-metamorpliism, that he considers it 

 unnecessary to discuss the facts and arguments that I have from 

 time to time brought forward to show that pressure before consolida- 

 tion was the efficient cause of the foliation of the Himalayan rock. 

 ] shall, as far as possible, refrain from repeating in this paper what 

 I have previously written on this subject, and shall content myself 

 with referring the reader to my address, as President of the 

 Geologists Association (Proc. Geol. Assoc, xiv, p. 287), for a con- 

 densed presentation of my case. On the present occasion I shall con- 

 fine my remarks to a statement of supplemental facts and arguments. 



Mr. Middlemiss's hypothesis, given in his own words, is as 

 follows : — " Just as the mineral composition of the great crystalline 

 axis of the Himalaya has been found to be the same right through 

 from end to end of the chain, so is it also found to be the case that 

 the dynamic metamorphism of those rocks is also a constant factor 

 throughout the range. 



" I do not think there can be two opinions as to the origin of this 

 state of things. It can only imply a steadily acting lateral pressure 

 of the earth's crust tending to bank it up against the central 

 crystalline core by a movement and a resistance in two opposite 

 directions. To the south we have the newer zones of disturbance 

 showing no dynamic metamorphism ; but to the north the accumu- 

 lated pressures consequent on the upheaval of several zones one 

 after the other, with the gradually diminishing in size of the larger 

 earth-folds as the centre of the solid crystalline core is approached, 

 have all tended to bring about that intense cleaving, shearing, and 

 deformation of the minuter particles of the rock which I embrace 

 generally under the head of dynamic metamorphism " (p. 279). 



The author tells us (p. 61) that the gneissose-granite "is present 

 in the form of intrusive bands among the schistose rocks " ; that these 

 " bands are generally parallel to the foliation of the rocks among 

 which they lie " ; and that the foliation of the granite is " perfectly 

 parallel to that of the schists " (p. 66). Some of the granite is 

 foliated, but some is not (p. 64). The non-foliated variety repre- 

 sents the " original condition in which the rock first solidified after 

 intrusion among the sedimentary rocks of the region " (p. 64) ; and 

 the foliated variety has been derived from it " by the mechanical 

 action of pressure metamorphism " (p. 64) ; " acting on the rock 

 since the time it became a solid stationary mass " (p. 65). 



The evidence on which the author appears to rely for proof of his 

 position may be summarized as follows : — 



(1) The crushed condition of the Himalayan rocks generally 

 (p. 279). 



(2) The parallel foliation and fissility of the rocks (p. 279). 



(3) The fact that the foliation of the gneissose-granite is usually 

 parallel to that of the schists, although there are exceptions to this 

 rule (p. 66). 



(4) That the gneissose-granite exhibits augen structure (p. 65). 



(5) That the minerals have been rolled and dragged out (p. 65), 

 and exhibit " flaser " structure (p. 72). 



