﻿ON 
  SECONDAEY 
  MINERALS 
  IN 
  CRYSTALLINE 
  ROCKS. 
  475 
  

  

  30. 
  On 
  the 
  Production 
  of 
  Secondary 
  Minerals 
  at 
  Shear-zones 
  in 
  

   the 
  Crystalline 
  Bocks 
  of 
  the 
  Malvern 
  Hills. 
  By 
  Charles 
  

   Callaavay, 
  D.Sc, 
  F.G.S. 
  (Bead 
  April 
  17, 
  1889.) 
  

  

  [Plate 
  XVI.] 
  

  

  Contents. 
  

   Introduction. 
  

   I. 
  Structural 
  and 
  Mineral 
  Changes 
  produced 
  at 
  Shear-zones. 
  

  

  A. 
  Structure 
  of 
  a 
  Shear-zone. 
  

  

  B. 
  Schistosity 
  in 
  Diorite. 
  

  

  C. 
  ,, 
  ,, 
  Granite. 
  

  

  D. 
  „ 
  „ 
  Felsite. 
  

  

  E. 
  „ 
  „ 
  Veined 
  Complexes. 
  

  

  1. 
  Production 
  in 
  Diorite 
  of 
  Micas, 
  Quartz, 
  and 
  Secondary 
  Felspar. 
  

  

  2. 
  Further 
  Mineral 
  changes. 
  

  

  3. 
  Descriptive 
  Notes 
  on 
  some 
  of 
  the 
  Minerals 
  by 
  Dr. 
  H. 
  B. 
  Patton. 
  

  

  4. 
  Exogenous 
  Origin 
  of 
  the 
  Granite-veins. 
  

  

  5. 
  Mineral 
  Aggregation 
  and 
  Enlargement. 
  

  

  6. 
  Introduction 
  of 
  new 
  Minerals 
  by 
  Infiltration. 
  

   II. 
  Chemical 
  Considerations. 
  

  

  III. 
  Temperature 
  of 
  Metamorphism. 
  

   Summary. 
  

  

  Introduction. 
  

  

  In 
  an 
  introductory 
  paper 
  * 
  read 
  before 
  this 
  Society 
  in 
  April 
  1887, 
  I 
  

   gave 
  a 
  rough 
  sketch 
  of 
  the 
  mode 
  in 
  which 
  certain 
  of 
  the 
  Malvern 
  

   schists 
  t 
  were 
  produced 
  ; 
  but 
  no 
  attempt 
  was 
  made 
  to 
  offer 
  a 
  com- 
  

   plete 
  solution 
  of 
  the 
  questions 
  discussed. 
  At 
  the 
  British 
  Association 
  

   in 
  1887 
  and 
  1888, 
  and 
  at 
  the 
  International 
  Geological 
  Congress 
  in 
  

   1888, 
  I 
  briefly 
  stated 
  certain 
  additional 
  results, 
  reserving 
  particulars 
  

   of 
  the 
  evidence 
  for 
  more 
  detailed 
  communications. 
  One 
  of 
  the 
  most 
  

   important 
  branches 
  of 
  the 
  inquiry 
  is 
  the 
  genesis 
  of 
  the 
  respective 
  

   minerals, 
  especially 
  of 
  the 
  micas. 
  If, 
  as 
  I 
  hope 
  to 
  prove, 
  some 
  of 
  

   the 
  most 
  abundant 
  minerals 
  are 
  of 
  secondary 
  origin, 
  the 
  ground 
  will 
  

   be 
  cleared 
  for 
  working 
  out 
  the 
  details 
  of 
  the 
  problem 
  in 
  hand. 
  

  

  Minute 
  particulars 
  of 
  rock- 
  composition 
  will 
  rarely 
  be 
  necessary 
  

   in 
  this 
  paper. 
  The 
  principal 
  varieties 
  of 
  the 
  Malvern 
  rocks 
  have 
  

   lately 
  been 
  carefully 
  described 
  by 
  Mr. 
  Butley 
  J, 
  and, 
  furthermore, 
  I 
  

   believe 
  that 
  the 
  question 
  is 
  to 
  be 
  settled 
  rather 
  by 
  field-evidence 
  

   than 
  by 
  the 
  study 
  of 
  minute 
  structure. 
  Indeed, 
  the 
  chief 
  results 
  

   were 
  decided 
  in 
  the 
  mind 
  of 
  the 
  writer 
  before 
  a 
  single 
  slide 
  had 
  

   been 
  cut. 
  Nevertheless 
  more 
  than 
  150 
  rock-sections 
  have 
  been 
  

   piepared. 
  Some 
  typical 
  examples 
  of 
  these 
  were 
  submitted 
  to 
  the 
  

   skilled 
  examination 
  of 
  Dr. 
  H. 
  B. 
  Patton, 
  assistant 
  to 
  Prof. 
  Bosen- 
  

   busch, 
  of 
  Heidelberg, 
  and 
  he 
  has 
  generously 
  permitted 
  me 
  to 
  incor- 
  

   porate 
  his 
  notes 
  in 
  this 
  communication 
  §. 
  My 
  thanks 
  are 
  also 
  due 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xliii. 
  p. 
  525. 
  

  

  + 
  By 
  " 
  schist 
  " 
  I 
  always 
  mean 
  " 
  crystalline 
  schist." 
  

  

  \ 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xliii. 
  p. 
  481. 
  

  

  | 
  Dr. 
  Patton's 
  identifications 
  of 
  minerals 
  were 
  in 
  all 
  material 
  points 
  iden- 
  

   tical 
  with 
  my 
  own. 
  A 
  few 
  cases 
  in 
  which 
  we 
  differed 
  I 
  have 
  excluded 
  from 
  

   consideration. 
  

  

  