﻿492 
  DR. 
  C. 
  CALLAWAY 
  ON 
  SECONDARY 
  MINERALS 
  IN 
  THE 
  

  

  the 
  Malvern 
  rocks 
  ; 
  but 
  I 
  have 
  not 
  been 
  able 
  to 
  find 
  that 
  they 
  have 
  

   any 
  material 
  bearing 
  on 
  my 
  inquiry. 
  Some 
  of 
  the 
  latter 
  is 
  probably 
  

   secondary, 
  but 
  a 
  part 
  of 
  it 
  is 
  apparently 
  original. 
  

  

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

  

  I 
  am 
  permitted 
  to 
  use 
  these 
  notes 
  at 
  my 
  discretion. 
  I 
  have 
  

   strictly 
  confined 
  myself 
  to 
  the 
  descriptive 
  matter 
  of 
  Dr. 
  Patton 
  's 
  

   letters, 
  but 
  I 
  have 
  added 
  such 
  remarks 
  as 
  are 
  necessary 
  to 
  connect 
  

   his 
  observations 
  with 
  my 
  line 
  of 
  inquiry. 
  The 
  extracts 
  will 
  be 
  

   indicated 
  by 
  inverted 
  commas. 
  

  

  Passage 
  from 
  diorite 
  (medium 
  black) 
  to 
  muscovite 
  chlorite-gneiss 
  

   (Nos. 
  325, 
  326, 
  327). 
  The 
  specimens 
  are 
  from 
  a 
  quarry 
  on 
  the 
  old 
  

   road 
  below 
  the 
  Wych, 
  on 
  the 
  east 
  side. 
  The 
  diorite 
  is 
  interlaced 
  

   with 
  a 
  few 
  large 
  granite-veins. 
  The 
  slides 
  are 
  taken 
  in 
  order 
  ; 
  325 
  

   being 
  12 
  inches 
  from 
  a 
  thick 
  vein, 
  326 
  and 
  327 
  within 
  3 
  inches. 
  

  

  " 
  No. 
  325. 
  A 
  compact 
  rock, 
  showing 
  no 
  trace 
  of 
  schistosity, 
  with 
  

   the 
  structure 
  and 
  composition 
  of 
  a 
  diorite. 
  The 
  principal 
  mineral, 
  

   forming 
  about 
  half 
  the 
  mass, 
  is 
  hornblende, 
  showing 
  little 
  tendency 
  

   to 
  idiomorphic 
  forms. 
  Here 
  and 
  there, 
  however, 
  we 
  can 
  recognize 
  

   the 
  faces 
  oo 
  P= 
  (110) 
  and 
  go 
  Poo 
  = 
  (010). 
  The 
  outlines 
  are 
  irregular, 
  

   wavy, 
  and 
  jaggy, 
  as 
  is 
  generally 
  the 
  case 
  with 
  diorite-hornblende. 
  

   The 
  ends 
  are 
  often 
  ravelled 
  out 
  into 
  a 
  fringe 
  of 
  needles. 
  It 
  possesses 
  

   the 
  cleavage-characteristics 
  of 
  hornblende, 
  and 
  also 
  the 
  high 
  index 
  

   of 
  refraction 
  and 
  moderate 
  interference-colours. 
  It 
  is 
  mostly 
  fresh, 
  

   or, 
  at 
  most, 
  changed 
  along 
  the 
  cleavage-planes 
  to 
  little 
  scales 
  of 
  

   chlorite. 
  

  

  "Feldspar 
  is 
  very 
  much 
  decomposed, 
  mostly 
  to 
  very 
  small, 
  irregular, 
  

   nearly 
  colourless 
  grains, 
  possessing 
  the 
  very 
  high 
  refractive 
  powers 
  

   and 
  the 
  brilliant 
  interference-colours 
  of 
  epidote. 
  The 
  original 
  

   plagioclase-twinning 
  has 
  totally 
  disappeared. 
  

  

  " 
  Quartz 
  in 
  rounded 
  grains 
  is 
  very 
  abundant, 
  and 
  easily 
  recog- 
  

   nized 
  by 
  its 
  clear 
  colour. 
  

  

  " 
  Biotite 
  is 
  apparently 
  wanting, 
  but 
  a 
  few 
  scales, 
  showing 
  the 
  

   properties 
  of 
  the 
  muscovite 
  in 
  No. 
  327, 
  are 
  scattered 
  about. 
  

  

  " 
  Grains 
  of 
  magnetite 
  or 
  possibly 
  ilmenite 
  are 
  scattered 
  abun- 
  

   dantly 
  through 
  the 
  slide. 
  They 
  are 
  often 
  associated 
  with 
  grains 
  of 
  

   great 
  refractive 
  powers 
  resembling 
  sphene. 
  

  

  " 
  No. 
  326. 
  This 
  rock 
  has 
  a 
  similar 
  composition 
  to 
  325, 
  but 
  a 
  

   schistose 
  structure 
  has 
  been 
  impressed 
  upon 
  it 
  by 
  the 
  drawing-out 
  

   of 
  the 
  hornblende 
  and, 
  to 
  a 
  still 
  greater 
  degree, 
  of 
  the 
  chlorite. 
  The 
  

   latter 
  appears 
  to 
  have 
  been 
  formed 
  at 
  the 
  expense 
  of 
  the 
  hornblende, 
  

   occasionally 
  almost 
  totally 
  replacing 
  it. 
  The 
  chlorite 
  is 
  positive 
  in 
  

   character, 
  and 
  is 
  easily 
  recognized 
  by 
  its 
  low 
  interference-colours 
  as 
  

   well 
  as 
  by 
  the 
  characteristic 
  pleochroism, 
  the 
  rays 
  vibrating 
  

   parallel 
  to 
  the 
  cleavage 
  being 
  green, 
  and 
  those 
  at 
  right 
  angles 
  to 
  

   the 
  same 
  yellow 
  or 
  reddish 
  to 
  colourless. 
  It 
  is 
  deposited 
  along 
  the 
  

   cleavage-planes 
  of 
  the 
  hornblende. 
  

  

  u 
  Feldsj>ar, 
  as 
  in 
  325, 
  is 
  very 
  much 
  decomposed, 
  being 
  changed 
  to 
  

   small 
  grains 
  .... 
  of 
  epidote. 
  

  

  