﻿500 
  DR. 
  C. 
  CALLAWAY 
  ON 
  SECONDARY 
  MINERALS 
  IN 
  THE 
  

  

  movement, 
  by 
  which 
  minerals 
  are 
  distorted 
  and 
  broken, 
  and 
  rock 
  

   in 
  the 
  mass 
  is 
  sliced 
  by 
  countless 
  planes 
  of 
  infiltration. 
  As 
  Mr. 
  

   Mellard 
  Reade* 
  contends, 
  following 
  M. 
  Tresca, 
  solid 
  rock 
  under 
  

   enormous 
  pressure 
  is 
  compelled 
  to 
  flow. 
  In 
  this 
  case, 
  the 
  pressure 
  

   must 
  have 
  been 
  approximately 
  horizontal, 
  and, 
  the 
  flow 
  being- 
  

   normal 
  to 
  the 
  direction 
  of 
  pressure, 
  the 
  dips 
  of 
  the 
  foliation 
  are 
  

   usually 
  at 
  very 
  high 
  angles. 
  

  

  But 
  where 
  we 
  find 
  an 
  ordinary 
  massive 
  diorite 
  with 
  cloudy 
  felspar, 
  

   passing 
  insensibly 
  into 
  a 
  rock 
  in 
  which 
  allotriomorphic 
  hornblende, 
  

   aggregated 
  into 
  seams, 
  alternates 
  with 
  transparent 
  clearly 
  twinned 
  

   felspar, 
  which 
  is 
  completely 
  moulded 
  to 
  the 
  curvilinear 
  margins 
  of 
  

   the 
  modified 
  hornblende, 
  to 
  the 
  angles 
  of 
  cleavage-fragments 
  of 
  the 
  

   same 
  mineral, 
  and 
  to 
  the 
  contours 
  of 
  decomposition-products, 
  such 
  

   as 
  chlorite 
  and 
  epidote, 
  we 
  are 
  driven 
  to 
  conclude 
  that 
  the 
  mechanical 
  

   cause 
  has 
  operated 
  in 
  conjunction 
  with 
  an 
  actual 
  fusion 
  or 
  solution 
  

   of 
  some 
  of 
  the 
  constituents. 
  Or 
  take 
  the 
  production 
  of 
  a 
  sound 
  

   gneiss 
  out 
  of 
  a 
  mass 
  of 
  crushed 
  granite 
  containing 
  infiltrated 
  decom- 
  

   position-products. 
  Much 
  of 
  the 
  orthoclase 
  is 
  reconstructed 
  in 
  

   small 
  crystals 
  or 
  in 
  granules, 
  secondary 
  granular 
  quartz 
  is 
  generated, 
  

   most 
  of 
  the 
  opaque 
  matter 
  in 
  the 
  cracks 
  is 
  chemically 
  absorbed, 
  and 
  

   direct 
  evidence 
  of 
  the 
  crushing 
  and 
  shearing 
  is 
  obliterated. 
  The 
  

   cleanest, 
  soundest 
  schists 
  generally 
  form 
  the 
  bands 
  of 
  maximum 
  

   shearing, 
  and 
  we 
  are 
  forced 
  to 
  infer 
  a 
  connexion 
  between 
  the 
  

   degree 
  of 
  reconstruction 
  and 
  the 
  degree 
  of 
  shearing. 
  On 
  the 
  whole, 
  

   it 
  seems 
  probable 
  that 
  the 
  pressure 
  generated 
  sufficient 
  heat 
  to 
  fuse 
  

   or 
  dissolve 
  some 
  of 
  the 
  rock 
  in 
  and 
  near 
  the 
  sheared 
  bands. 
  

  

  Solution 
  appears 
  more 
  probable 
  than 
  fusion. 
  The 
  action 
  of 
  water 
  

   is 
  shown 
  by 
  the 
  abundance 
  of 
  chlorite 
  and 
  calcite, 
  and 
  by 
  the 
  other 
  

   decomposition-products 
  which 
  have 
  been 
  infiltrated 
  into 
  shear-planes 
  

   and 
  cracks 
  in 
  crystals. 
  The 
  most 
  recent 
  chemical 
  researches 
  prove 
  

   that 
  a 
  very 
  minute 
  proportion 
  of 
  water 
  will 
  suffice 
  to 
  hold 
  a 
  silicate 
  

   in 
  solution. 
  The 
  comparative 
  solubility 
  of 
  felspar 
  is 
  illustrated 
  by 
  the 
  

   frequency 
  of 
  the 
  occurrence 
  of 
  fragments 
  of 
  crushed 
  hornblende- 
  

   crystals 
  as 
  inclusions 
  in 
  clear 
  plagioclase. 
  

  

  Whether 
  the 
  whole 
  of 
  the 
  diorite 
  and 
  granite 
  had 
  consolidated 
  

   before 
  the 
  chief 
  mechanical 
  force 
  came 
  into 
  operation 
  is 
  not 
  easy 
  

   to 
  determine, 
  but 
  an 
  affirmative 
  answer 
  is 
  probable. 
  The 
  granite 
  

   is 
  certainly 
  younger 
  than 
  the 
  diorites, 
  yet 
  in 
  numerous 
  cases 
  exa- 
  

   mined 
  the 
  first 
  stage 
  in 
  the 
  conversion 
  of 
  the 
  granite 
  into 
  gneiss 
  

   is 
  the 
  crushing 
  of 
  the 
  rigid 
  rock 
  into 
  a 
  mass 
  of 
  lenticular 
  fragments. 
  

   The 
  Ragged-Stone-Hill 
  felsite, 
  too, 
  which 
  penetrates 
  the 
  coarse 
  grey 
  

   diorite 
  (the 
  younger 
  of 
  the 
  two 
  chief 
  varieties), 
  is 
  sometimes 
  sheared 
  

   like 
  a 
  solid 
  mass. 
  If 
  any 
  parts 
  of 
  the 
  Malvern 
  complex 
  had 
  not 
  

   consolidated 
  before 
  metamorphism, 
  they 
  were 
  in 
  a 
  very 
  small 
  pro- 
  

   portion. 
  

  

  The 
  views 
  to 
  which 
  the 
  writer 
  has 
  been 
  led 
  by 
  the 
  study 
  of 
  the 
  

   Malvern 
  rocks 
  agree 
  in 
  the 
  main 
  with 
  the 
  modern 
  theories 
  of 
  

   dynamic 
  metamorphism 
  ; 
  but 
  the 
  chemical 
  changes 
  here 
  recorded 
  

   appear 
  to 
  be 
  greater 
  than 
  any 
  previously 
  observed. 
  

   * 
  Origin 
  of 
  Mountain-Kanges, 
  p. 
  168. 
  

  

  