﻿532 
  MAJOR-GENERAL 
  C. 
  A. 
  m'MAHON 
  ON 
  THE 
  HORNBLENDE-SCHISTS 
  

  

  a 
  tabular 
  form 
  of 
  the 
  result 
  of 
  the 
  microscopic 
  examination 
  of 
  some 
  

   samples 
  of 
  them 
  collected 
  by 
  me. 
  

  

  No. 
  

  

  Locality 
  from 
  which 
  the 
  

   specimens 
  were 
  taken. 
  

  

  Pentreath 
  Beach 
  H 
  

  

  ditto 
  H 
  

  

  Pen 
  Voose 
  H 
  

  

  ditto 
  \R 
  

  

  Cadgwith 
  iH 
  

  

  ditto 
  ... 
  H 
  

  

  Pen 
  Voose 
  H 
  

  

  Pentreath 
  H 
  

  

  Flag-staff 
  Quarry, 
  Cadgwith 
  . 
  |H 
  

  

  Pen 
  Voose 
  H 
  

  

  Kennack 
  Cove 
  H 
  

  

  Pen 
  Voose 
  H 
  

  

  ditto 
  

  

  ditto 
  ... 
  

  

  Flag-staff 
  Quarry, 
  Cadgwith 
  

  

  ditto 
  ... 
  

  

  Pentreath 
  

  

  Kennack 
  Cove 
  \ 
  . 
  . 
  . 
  

  

  ditto 
  

  

  7i 
  

  

  Q 
  Mi 
  

   Q.Mi 
  

   QjMi 
  

   Q 
  Mi 
  

   QjMi 
  

   Q, 
  ! 
  Mi 
  

   Q! 
  Mi 
  

   ... 
  Mi 
  

   ...I 
  Mi 
  

   ...I 
  Mi 
  

   ... 
  

  

  Q 
  Mi 
  

   Q 
  ' 
  Mi 
  

   Q 
  Mi 
  

   Q 
  Mi 
  

   QMi 
  

   ... 
  Mi 
  

   ... 
  Mi 
  

   ...Mi 
  

  

  -2 
  

  

  

  *-+j 
  

  

  

  c3 
  

  

  J3 
  

  

  P- 
  

  

  P, 
  

  

  < 
  

  

  w. 
  

  

  Ap 
  

  

  Sph 
  

  

  Ap 
  

  

  Sph 
  

  

  Ap 
  

  

  Sph 
  

  

  Ap 
  

  

  Sph 
  

  

  Ap 
  Sph 
  

   Ap 
  Sph 
  

   Ap 
  Sph 
  

   Ap 
  | 
  ... 
  

   Ap 
  Sph 
  

  

  ;;; 
  s 
  P 
  h 
  

  

  Ma 
  

   Ma 
  

  

  Ma 
  

  

  Ma 
  

  

  Ma 
  

  

  Ma 
  

   Ma 
  

  

  Ap 
  

  

  Ap 
  Sph 
  Ma 
  

  

  Ap 
  Sph 
  ... 
  

  

  Ap 
  Sph 
  Ma 
  

  

  Ma 
  

  

  Ap 
  

  

  Chi 
  

  

  Chi 
  

  

  cm 
  

  

  Chi 
  

  

  w 
  

  

  w 
  

  

  f 
  w 
  

  

  Granites 
  undoubtedly 
  intrusive 
  in 
  the 
  " 
  Granulitic 
  " 
  group. 
  

  

  Pen 
  Voose 
  

   ditto 
  ... 
  

  

  Cadgwith 
  

   ditto 
  ... 
  

  

  ...'F 
  Q 
  

  

  ...|F|Q 
  

   ...F 
  Q 
  

  

  122316 
  

  

  Mi 
  

  

  Mi 
  

   Mi 
  

   Mi 
  

  

  22 
  

  

  Ap 
  

   Ap 
  

   Ap 
  

   Ap 
  

  

  IS 
  

  

  12 
  

  

  10 
  

  

  f. 
  Indicates 
  that 
  these 
  specimens 
  are 
  more 
  or 
  less 
  foliated, 
  

   b. 
  Specimens 
  taken 
  from 
  black 
  bands 
  in 
  the 
  granulitic 
  rocks, 
  

   w. 
  Specimens 
  taken 
  from 
  white 
  bands 
  in 
  the 
  granulitic 
  rocks. 
  

  

  Felspar, 
  it 
  will 
  be 
  observed, 
  is 
  common 
  to 
  all 
  the 
  specimens. 
  It 
  

   forms 
  the 
  base 
  in 
  which 
  the 
  other 
  minerals 
  are 
  imbedded, 
  and 
  here 
  

   and 
  there 
  it 
  exhibits 
  the 
  twinning 
  of 
  plagioclase. 
  It 
  is 
  generally 
  

   more 
  or 
  less 
  decomposed, 
  but 
  it 
  is 
  occasionally 
  water-clear. 
  

  

  The 
  felspar 
  in 
  all 
  these 
  rocks 
  affords 
  more 
  or 
  less 
  evidence 
  of 
  

   incipient 
  saussurization 
  : 
  round 
  patches, 
  opaque 
  in 
  transmitted 
  light, 
  

   and 
  of 
  pearly 
  white 
  colour 
  in 
  reflected 
  light, 
  have 
  been 
  formed 
  here 
  

   and 
  there, 
  which 
  have 
  no 
  definite 
  relation 
  to 
  the 
  shape 
  of 
  the 
  crystals 
  

   containing 
  them. 
  Possibly 
  the 
  granular 
  appearance 
  often 
  given 
  to 
  

   the 
  rock 
  by 
  these 
  white 
  spots 
  may 
  have 
  suggested 
  the 
  term 
  " 
  granu- 
  

   lite." 
  If 
  so 
  it 
  simply 
  denotes 
  the 
  progress 
  of 
  decay 
  and 
  gives 
  no 
  

   clue 
  to 
  the 
  original 
  structure 
  of 
  the 
  rock. 
  

  

  Mica 
  is 
  another 
  mineral 
  found 
  in 
  all 
  but 
  one 
  of 
  the 
  samples. 
  

   The 
  predominant 
  type 
  is 
  a 
  mica 
  at 
  one 
  end 
  of 
  the 
  scale 
  and 
  a 
  chlorite 
  

   at 
  the 
  other 
  ; 
  but 
  it 
  is 
  often 
  difficult 
  to 
  say 
  regarding 
  the 
  interme- 
  

  

  