﻿216 
  J. 
  A. 
  PHILLIPS 
  ON 
  CERTAIN 
  

  

  22. 
  Additional 
  Note 
  on 
  Certain 
  Inclusions 
  in 
  Granites. 
  By 
  

   J. 
  Arthur 
  Phillips, 
  Esq., 
  F.R.S., 
  F.G.S. 
  (Read 
  March 
  8, 
  

  

  188*2.) 
  

  

  In 
  a 
  paper 
  which 
  I 
  had 
  the 
  honour 
  of 
  reading 
  before 
  this 
  Society 
  on 
  

   November 
  19th, 
  1879, 
  entitled 
  "On 
  Concretionary 
  Patches 
  and 
  

   Fragments 
  of 
  other 
  Rocks 
  contained 
  in 
  Granite," 
  I 
  called 
  attention 
  

   to 
  the 
  fact 
  that 
  a 
  certain 
  class 
  of 
  snch 
  inclusions, 
  usually 
  more 
  or 
  

   less 
  ovoid 
  in 
  form 
  and 
  resembling 
  imbedded 
  pebbles, 
  are 
  essentially 
  

   composed 
  of 
  a 
  fine-grained 
  variety 
  of 
  the 
  granite 
  in 
  which 
  they 
  are 
  

   severally 
  enclosed. 
  The 
  proportion 
  of 
  dark-coloured 
  mica 
  in 
  these 
  

   patches 
  is 
  almost 
  invariably 
  greater 
  than 
  in 
  the 
  rock 
  in 
  which 
  they 
  

   occur, 
  and 
  imparts 
  to 
  them 
  a 
  darker 
  colour 
  than 
  that 
  of 
  the 
  general 
  

   mass. 
  It 
  was 
  further 
  observed, 
  when 
  sections 
  made 
  through 
  both 
  

   pebble-like 
  inclusions 
  and 
  the 
  enclosing 
  granite 
  are 
  examined 
  under 
  

   the 
  microscope, 
  that 
  along 
  their 
  line 
  of 
  contact 
  minute 
  crystals 
  

   are 
  found 
  to 
  extend 
  from 
  the 
  one 
  into 
  the 
  other. 
  These 
  rounded 
  

   inclusions 
  sometimes 
  enclose 
  a 
  second 
  similar 
  nodule, 
  differing 
  from 
  

   the 
  first 
  either 
  in 
  colour 
  or 
  in 
  fineness 
  of 
  grain 
  only. 
  

  

  Such 
  inclusions 
  are 
  sometimes 
  porphyritic 
  in 
  structure, 
  and 
  enclose 
  

   large 
  crystals 
  of 
  the 
  felspar 
  characterizing 
  the 
  enclosing 
  rock. 
  Thus, 
  

   when 
  the 
  felspar 
  of 
  the 
  surrounding 
  granite 
  is 
  either 
  red 
  or 
  pink 
  in 
  

   colour, 
  that 
  which 
  is 
  porphyritically 
  distributed 
  through 
  the 
  inclu- 
  

   sions 
  will 
  be 
  correspondingly 
  red 
  or 
  pink 
  ; 
  if, 
  on 
  the 
  contrary, 
  white 
  

   felspar 
  be 
  a 
  characteristic 
  of 
  the 
  normal 
  granite, 
  the 
  porphyritic 
  

   crystals 
  of 
  the 
  inclusions 
  will 
  likewise 
  be 
  white. 
  The 
  angles 
  of 
  

   felspar 
  crystals 
  so 
  enclosed 
  in 
  ovoid 
  inclusions 
  are 
  often 
  much 
  

   rounded. 
  

  

  Arguing 
  from 
  these 
  facts, 
  I 
  had 
  concluded 
  that 
  rounded 
  " 
  inclu- 
  

   sions" 
  are 
  usually 
  contemporaneous 
  with 
  the 
  consolidation 
  of 
  the 
  

   general 
  rock-mass, 
  and 
  that 
  they 
  are 
  due 
  to 
  the 
  action 
  of 
  forces 
  of 
  

   somewhat 
  the 
  same 
  nature 
  as 
  those 
  which 
  have 
  resulted 
  in 
  the 
  

   production 
  of 
  the 
  concretionary 
  nodules 
  of 
  the 
  orbicular 
  diorite 
  of 
  

   Corsica. 
  

  

  Up 
  to 
  the 
  time 
  of 
  the 
  publication 
  of 
  the 
  paper 
  referred 
  to, 
  

   although 
  constantly 
  sought 
  for, 
  no 
  instance 
  had 
  been 
  met 
  with 
  of 
  

   the 
  penetration 
  of 
  large 
  crystals 
  of 
  felspar 
  from 
  the 
  surrounding 
  

   granite 
  into 
  one 
  of 
  these 
  pebble-like 
  inclusions. 
  More 
  recently, 
  

   however, 
  numerous 
  examples 
  have 
  been 
  observed 
  of 
  a 
  crystal 
  of 
  

   felspar 
  from 
  the 
  granite 
  penetrating 
  an 
  inclusion, 
  or 
  one 
  of 
  the 
  

   porphyritic 
  felspar 
  crystals 
  of 
  an 
  inclusion 
  extending 
  into 
  the 
  

   granite. 
  

  

  The 
  accompanying 
  woodcuts, 
  after 
  drawings 
  by 
  Mr. 
  Frank 
  Rutley, 
  

   represent, 
  one 
  half 
  natural 
  size, 
  a 
  dark 
  inclusion 
  and 
  a 
  portion 
  of 
  a 
  

   nearly 
  similar 
  one, 
  penetrated 
  by 
  large 
  crystals 
  of 
  red 
  microcline, 
  in 
  

   Shap 
  granite 
  forming 
  part 
  of 
  the 
  fagade 
  of 
  a 
  building 
  in 
  Nicholas 
  

  

  