﻿CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  MALVERN 
  HILLS. 
  503 
  

  

  Dr. 
  Irving 
  alluded 
  to 
  the 
  important 
  difference 
  presented 
  by 
  the 
  

   phenomena 
  of 
  the 
  shear-zones 
  and 
  those 
  of 
  the 
  masses 
  of 
  the 
  

   gneisses. 
  We 
  have 
  no 
  right 
  to 
  assume 
  that 
  these 
  rocks 
  are 
  meta- 
  

   morphic 
  in 
  their 
  origin. 
  The 
  question 
  of 
  the 
  replacement 
  of 
  bases 
  

   is 
  one 
  of 
  much 
  interest. 
  He 
  explained 
  how 
  potash 
  may 
  be 
  

   replaced, 
  and 
  gave 
  illustrations 
  : 
  there 
  would 
  be 
  variations 
  in 
  the 
  

   results 
  according 
  to 
  the 
  quantity 
  of 
  free 
  carbonic 
  acid 
  acting 
  on 
  the 
  

   silicates. 
  

  

  The 
  Author, 
  in 
  reply, 
  stated 
  that 
  he 
  had 
  not 
  raised 
  the 
  general 
  

   question 
  as 
  to 
  the 
  origin 
  of 
  the 
  crystalline 
  schists. 
  Mr. 
  Rutley 
  

   recognized 
  sedimentary 
  rocks 
  towards 
  the 
  south 
  end 
  of 
  the 
  chain. 
  

   This 
  appearance 
  was 
  simply 
  due 
  to 
  more 
  intense 
  shearing. 
  The 
  

   rocks 
  were 
  more 
  highly 
  quartzose, 
  the 
  result 
  of 
  more 
  intense 
  

   metamorphism. 
  The 
  crushed 
  rock 
  gradually 
  passes 
  into 
  the 
  recon- 
  

   structed 
  rock. 
  He 
  allowed 
  that 
  black 
  mica 
  may 
  be 
  derived 
  directly 
  

   from 
  hornblende, 
  but 
  that 
  was 
  not 
  the 
  case 
  in 
  the 
  Malvern 
  Hills. 
  

   He 
  dissented 
  from 
  the 
  notion 
  of 
  friction-breccia. 
  Mr. 
  Teall's 
  

   point 
  was 
  the 
  kernel 
  of 
  the 
  whole 
  question. 
  There 
  was 
  deformation 
  

   at 
  the 
  margins 
  of 
  the 
  zones, 
  but 
  not 
  in 
  the 
  centre, 
  because 
  the 
  rock 
  

   had 
  been 
  reconstructed 
  ; 
  eyes 
  of 
  felspar 
  are 
  often 
  seen 
  in 
  the 
  most 
  

   highly 
  fohated 
  rocks. 
  A 
  granular 
  structure 
  was 
  characteristic 
  of 
  

   the 
  reconstructed 
  bands. 
  There 
  was 
  no 
  distinction 
  between 
  smaller 
  

   and 
  larger 
  granite-veins. 
  He 
  referred 
  to 
  Prof. 
  Blake's 
  point 
  as 
  

   to 
  the 
  evidence 
  of 
  shearing 
  in 
  the 
  broken 
  hornblende 
  crystals. 
  

   Most 
  of 
  the 
  questions 
  raised 
  were 
  answered 
  in 
  the 
  paper. 
  

  

  