﻿CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  MALVERN 
  HILLS. 
  489 
  

  

  latin 
  g 
  sericitic 
  bundles 
  thickest 
  in 
  the 
  middle. 
  Its 
  colours 
  of 
  polari- 
  

   zation 
  are 
  clear 
  and 
  vivid, 
  not 
  in 
  uniform 
  sheets, 
  but 
  with 
  a 
  rather 
  

   blotchy 
  aspect, 
  except 
  when 
  the 
  fibres 
  or 
  laminae 
  are 
  distinctly 
  defined. 
  

   This 
  mica 
  is 
  associated 
  with 
  chlorite. 
  The 
  latter 
  sometimes 
  occurs 
  

   in 
  small 
  isolated 
  patches 
  ; 
  but 
  a 
  large 
  proportion 
  of 
  it 
  surrounds 
  the 
  

   mica-bundles, 
  and 
  lies 
  within 
  them, 
  sometimes 
  in 
  irregular 
  blotches. 
  

   The 
  chlorite 
  of 
  some 
  of 
  these 
  blotches 
  gradually 
  passes 
  into 
  the 
  

   non-fibrous 
  part 
  of 
  the 
  mica. 
  By 
  plain 
  light 
  the 
  green 
  colour 
  of 
  

   the 
  former 
  is 
  seen 
  to 
  be 
  densest 
  in 
  the 
  middle 
  of 
  the 
  blotch, 
  and 
  it 
  

   shades 
  off 
  into 
  the 
  transparency 
  of 
  the 
  enclosing 
  mica. 
  Under 
  

   crossed 
  nicols 
  the 
  chlorite 
  is 
  of 
  a 
  mottled 
  black 
  colour 
  in 
  the 
  centre, 
  

   and 
  it 
  graduates 
  outwardly 
  into 
  a 
  grey, 
  which 
  shades 
  through 
  white, 
  

   orange, 
  and 
  red 
  into 
  the 
  blues 
  and 
  greens 
  of 
  the 
  second 
  order. 
  The 
  

   nucleus 
  of 
  the 
  chlorite-blotch 
  remains 
  dark 
  during 
  an 
  entire 
  rotation 
  

   of 
  the 
  stage, 
  the 
  mica 
  extinguishing 
  as 
  its 
  fibres 
  are 
  brought 
  into 
  

   parallelism 
  with 
  the 
  axis 
  of 
  a 
  nicol. 
  A 
  large 
  quantity 
  of 
  opaque 
  

   matter 
  in 
  irregular 
  angular 
  particles 
  is 
  enclosed 
  in 
  both 
  chlorite 
  

   and 
  mica, 
  and 
  is 
  probably 
  part 
  of 
  the 
  iron-oxide 
  liberated 
  in 
  the 
  

   general 
  metamorphosis. 
  The 
  fine 
  lines 
  in 
  the 
  white 
  mica 
  probably 
  

   also 
  indicate 
  liberation 
  of 
  iron. 
  

  

  Other 
  slides 
  from 
  the 
  same 
  band 
  of 
  rock 
  show 
  a 
  more 
  complete 
  

   change, 
  the 
  mica 
  being 
  in 
  still 
  greater 
  proportion 
  and 
  the 
  chlorite 
  

   being 
  nearly 
  or 
  entirely 
  absent. 
  I 
  am 
  unable 
  to 
  explain 
  the 
  facts 
  

   here 
  described 
  except 
  on 
  the 
  supposition 
  that 
  the 
  mica 
  has 
  been 
  

   formed 
  from 
  the 
  chlorite. 
  

  

  The 
  possibility 
  that 
  the 
  mineral 
  which 
  I 
  have 
  described 
  as 
  mica 
  

   was 
  talc 
  at 
  first 
  occurred 
  to 
  me 
  ; 
  but 
  two 
  analyses 
  of 
  this 
  schist, 
  

   kindly 
  made 
  for 
  me 
  under 
  the 
  direction 
  of 
  Dr. 
  G. 
  H. 
  Bailey, 
  of 
  Oweus 
  

   College, 
  Manchester, 
  giving 
  respectively 
  only 
  1'29 
  and 
  0*35 
  per 
  cent, 
  

   of 
  magnesia, 
  forbid 
  the 
  supposition. 
  

  

  Garnets 
  and 
  Zoisite. 
  — 
  Garnets 
  are 
  not 
  common 
  at 
  Malvern, 
  as 
  

   only 
  three 
  or 
  four 
  slides 
  in 
  my 
  collection 
  contain 
  them 
  in 
  noticeable 
  

   quantity. 
  No. 
  357 
  is 
  from 
  the 
  crest 
  of 
  Swinyard's 
  Hill, 
  south 
  of 
  

   the 
  summit. 
  It 
  is 
  modified 
  kersantite 
  with 
  two 
  parallel 
  granite- 
  

   veins 
  included. 
  At 
  one 
  side 
  of 
  the 
  slide 
  is 
  a 
  highly 
  quartzose 
  vein, 
  

   only 
  a 
  few 
  shreds 
  of 
  curvilinear 
  felspar 
  remaining, 
  and 
  the 
  second 
  

   vein, 
  which 
  is 
  at 
  the 
  opposite 
  side, 
  is 
  entirely 
  of 
  quartz. 
  The 
  inter- 
  

   mediate 
  foliated 
  kersantite 
  becomes 
  progressively 
  quartzose 
  towards 
  

   the 
  latter. 
  At 
  first 
  it 
  contains 
  little 
  quartz, 
  then 
  the 
  felspar 
  is 
  more 
  

   and 
  more 
  replaced 
  by 
  quartz, 
  till, 
  in 
  some 
  parts 
  of 
  the 
  slide, 
  the 
  

   quartz 
  is 
  to 
  the 
  felspar 
  and 
  mica 
  in 
  the 
  proportion 
  of 
  five 
  or 
  six 
  to 
  one. 
  

   At 
  the 
  contact 
  with 
  the 
  quartz-vein 
  the 
  felspar 
  is 
  rather 
  more 
  

   abundant. 
  In 
  the 
  more 
  quartzose, 
  and 
  presumably 
  the 
  more 
  altered, 
  

   parts, 
  there 
  is 
  less 
  black 
  mica 
  than 
  usual, 
  and 
  garnets 
  appear 
  ; 
  they 
  

   are 
  also 
  abundant 
  round 
  the 
  margin 
  of 
  the 
  quartz-vein. 
  They 
  are 
  

   of 
  small 
  size, 
  the 
  largest 
  being 
  not 
  more 
  than 
  2 
  mm. 
  in 
  diameter, 
  

   mostly 
  in 
  single 
  or 
  compound 
  granules 
  of 
  irregular 
  form, 
  translucent 
  

   or 
  rather 
  cloudy, 
  showing 
  strong 
  refraction, 
  and, 
  between 
  crossed 
  

   nicols, 
  remaining 
  dark 
  during 
  an 
  entire 
  rotation 
  of 
  the 
  stage. 
  

  

  No. 
  356 
  is 
  from 
  another 
  part 
  of 
  the 
  same 
  mass. 
  A 
  part 
  of 
  the 
  

  

  