﻿522 
  MAJOE-GENEEAL 
  C. 
  A. 
  M'MAHON 
  ON 
  THE 
  HOEKBLENDE-SCHISTS 
  

  

  Table 
  of 
  Hornblende-schists. 
  

  

  Localities 
  from 
  which 
  the 
  

   specimens 
  were 
  taken. 
  

  

  T3 
  j 
  

  

  e 
  Hi 
  §° 
  

  

  Wit* 
  ^ 
  

  

  Between 
  Caerthilhan 
  and 
  

  

  Lizard 
  Head 
  

  

  Bumble 
  

  

  Penolver 
  Point 
  

  

  Quarry 
  between 
  Landewed- 
  

   nack 
  Church 
  and 
  Church 
  

   cove 
  

  

  Ditto 
  

  

  Ditto 
  

  

  Church 
  Cove 
  

  

  Cove 
  between 
  Church 
  Cove 
  

   and 
  Pen 
  Voose 
  

  

  Ditto 
  

  

  Ditto 
  

  

  Chough 
  Ogo 
  

  

  Cam 
  Barrow 
  

  

  Ditto 
  

  

  Ditto 
  

  

  Ditto 
  

  

  Cadgwith 
  

  

  H 
  F 
  

  

  HF 
  

   HF 
  

  

  HF 
  

   HF 
  

   HF 
  

   H 
  F 
  

  

  H 
  F 
  

   H 
  F 
  

  

  1616 
  

  

  Aug 
  

  

  Aug 
  

   Aug 
  

   Aug 
  

   Aug 
  

  

  Sph 
  

   Sph 
  

  

  Sph 
  

   Sph 
  

   Sph 
  

   Sph 
  

  

  Sph 
  

   Sph 
  

   Sph 
  

   Sph 
  

  

  Sph 
  

   Sph 
  

  

  Ma 
  

  

  Ap 
  

  

  Ap 
  Ma 
  

  

  Ap 
  

   Ap 
  

  

  Ap 
  

   Ap 
  

  

  Ma 
  

  

  Ma 
  

   Ma 
  

  

  Ma 
  

   Ma 
  

   Ma 
  

   Ma 
  

   Ma 
  

  

  12 
  I 
  7 
  10 
  

  

  Py 
  

  

  

  Ep 
  

  

  Ep 
  

  

  Py| 
  

   Pyi 
  

  

  ... 
  i 
  

  

  Py 
  

   p 
  y| 
  

  

  Ca 
  

  

  Ca 
  

   Ca 
  

   Ca 
  

  

  Chi 
  

   Chi 
  

   Chi 
  

  

  £ 
  

  

  Mi 
  

  

  An 
  

  

  Sphene, 
  it 
  will 
  be 
  seen, 
  is 
  present 
  in 
  nearly 
  all 
  the 
  specimens 
  ; 
  

   apatite 
  may 
  be 
  detected 
  in 
  7 
  out 
  of 
  the 
  16 
  samples, 
  whilst 
  iron, 
  in 
  

   the 
  form 
  of 
  magnetite, 
  pyrites, 
  or 
  ferrite, 
  is 
  common. 
  

  

  Carbonate 
  of 
  lime 
  occurs 
  in 
  four 
  slides 
  ; 
  epidote 
  in 
  two 
  ; 
  mica 
  

   and 
  analcime 
  in 
  one 
  each. 
  

  

  The 
  most 
  unexpected 
  mineral 
  found 
  in 
  these 
  schists 
  is 
  malacolite 
  or 
  

   a 
  colourless 
  augite 
  ; 
  it 
  occurs 
  in 
  five 
  of 
  the 
  specimens 
  entered 
  in 
  the 
  

   foregoing 
  list, 
  and 
  as 
  its 
  presence 
  in 
  the 
  hornblende-schists 
  of 
  the 
  

   Lizard 
  has 
  not 
  hitherto 
  been 
  noted, 
  it 
  may 
  be 
  as 
  well 
  to 
  give 
  some 
  

   details 
  regarding 
  it. 
  No. 
  3 
  of 
  this 
  list 
  was 
  taken 
  from 
  the 
  top 
  and 
  

   extreme 
  edge 
  of 
  an 
  inaccessible 
  cliff 
  at 
  Penolver 
  Point. 
  This 
  is 
  a 
  some- 
  

   what 
  remarkable 
  rock 
  ; 
  macroscopically 
  examined 
  it 
  does 
  not 
  materially 
  

   differ 
  in 
  appearance 
  from 
  an 
  ordinary 
  hornblende-rock 
  in 
  which 
  the 
  

   foliation 
  is 
  obscure 
  ; 
  but 
  under 
  the 
  microscope 
  it 
  is 
  seen 
  to 
  be 
  a 
  finely 
  

   granular 
  mixture 
  of 
  felspar, 
  augite, 
  hornblende, 
  and 
  sphene. 
  It 
  is 
  

   perfectly 
  noncrystalline 
  in 
  structure. 
  The 
  augite 
  is 
  in 
  rounded 
  gran- 
  

   ules 
  and 
  it 
  is 
  almost 
  as 
  abundant 
  as 
  the 
  felspar. 
  The 
  hornblende 
  is 
  a 
  

   secondary 
  product 
  and 
  it 
  is 
  more 
  abundant 
  along 
  one 
  zone 
  than 
  in 
  the 
  

   rest 
  of 
  the 
  slice. 
  Indeed 
  this 
  tendency 
  of 
  the 
  hornblende 
  to 
  arrange 
  

   itself 
  in 
  zones 
  constitutes 
  what 
  there 
  is 
  of 
  foliation 
  in 
  the 
  rock. 
  The 
  

   augite 
  and 
  felspar 
  exhibit 
  no 
  parallelism 
  in 
  the 
  mutual 
  arrangement 
  

   or 
  in 
  the 
  orientation 
  of 
  their 
  crystals. 
  The 
  slice 
  supplies 
  abundant 
  

  

  * 
  This 
  includes 
  ilmenite 
  and 
  ferrite. 
  

  

  