﻿CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  MALVERN 
  HILLS. 
  491 
  

  

  planes 
  of 
  the 
  chlorite 
  and 
  the 
  mica 
  points 
  to 
  the 
  secondary 
  origin 
  of 
  

   both 
  of 
  these 
  minerals. 
  If, 
  on 
  the 
  other 
  hand, 
  the 
  mica 
  is 
  an 
  

   original 
  product, 
  we 
  seem 
  driven 
  to 
  reverse 
  the 
  series 
  of 
  changes, 
  

   and 
  to 
  conclude 
  that 
  the 
  sphene 
  of 
  the 
  mica, 
  and 
  subsequently 
  of 
  

   the 
  chlorite, 
  is 
  changed 
  to 
  ilmenite 
  and 
  enclosed 
  in 
  hornblende, 
  for 
  

   the 
  granular 
  leucoxene, 
  with 
  its 
  nucleus 
  of 
  ore, 
  is 
  often 
  more 
  or 
  

   less 
  surrounded 
  by 
  that 
  mineral. 
  

  

  Actinolite. 
  — 
  Near 
  the 
  summit 
  of 
  the 
  Eagged 
  Stone 
  Hill 
  is 
  a 
  rock 
  

   which 
  Mr. 
  Teall 
  considers 
  * 
  " 
  identical 
  with 
  many 
  Cornish 
  epi- 
  

   cliorites," 
  such 
  as 
  have 
  been 
  described 
  by 
  Mr. 
  Allport, 
  Mr. 
  J. 
  A. 
  

   Phillips, 
  and 
  more 
  recently 
  by 
  himself 
  f. 
  Three 
  specimens 
  were 
  

   taken 
  along 
  a 
  line 
  parallel 
  with 
  an 
  adjacent 
  felsite-dyke. 
  One 
  

   slide 
  (343) 
  contains 
  uralite, 
  actinolite, 
  epidote, 
  and 
  felspar. 
  The 
  

   uralite 
  rarely 
  presents 
  the 
  true 
  form 
  of 
  augite, 
  but 
  is 
  usually 
  in 
  

   irregularly 
  tabular 
  sections 
  with 
  rounded 
  angles. 
  It 
  is 
  feebly 
  

   pleochroic. 
  It 
  shades 
  off, 
  often 
  in 
  the 
  same 
  crystal, 
  into 
  acicular 
  

   actinolite, 
  which 
  entirely 
  replaces 
  it 
  in 
  some 
  parts 
  of 
  the 
  slide. 
  

   The 
  epidote 
  is 
  in 
  numerous 
  highly 
  polarizing 
  granules. 
  The 
  felspar 
  

   is 
  tolerably 
  clear, 
  displaying 
  no 
  twinning, 
  and 
  merely 
  filling 
  in 
  

   spaces 
  between 
  the 
  other 
  minerals, 
  often 
  enclosing 
  spicules 
  of 
  

   actinolite 
  and 
  grains 
  of 
  epidote. 
  It 
  is 
  obviously 
  secondary, 
  as 
  ob- 
  

   served 
  by 
  Mr. 
  Teall 
  % 
  with 
  reference 
  to 
  a 
  similar 
  rock 
  near 
  Tavistock. 
  

  

  A 
  second 
  specimen 
  (342), 
  a 
  few 
  feet 
  to 
  the 
  north 
  in 
  the 
  same 
  

   mass, 
  is 
  almost 
  exclusively 
  composed 
  of 
  actinolite 
  and 
  felspar 
  in 
  

   about 
  equal 
  proportions. 
  It 
  is 
  semi-schistose, 
  this 
  structure 
  being- 
  

   due 
  to 
  a 
  rough 
  parallelism 
  of 
  the 
  spicules 
  of 
  actinolite, 
  which 
  often 
  

   coincide 
  in 
  direction 
  with 
  irregular 
  undulating 
  lines 
  of 
  fracture 
  

   (shear-planes). 
  Some 
  of 
  the 
  felspar 
  is 
  in 
  elongated 
  prisms 
  and 
  

   shows 
  polysynthetic 
  twinning. 
  

  

  A 
  few 
  feet 
  further 
  to 
  the 
  north, 
  and 
  continuous 
  on 
  the 
  strike 
  

   with 
  the 
  last-named 
  rock, 
  is 
  a 
  narrow 
  band 
  of 
  a 
  green 
  schist 
  (345), 
  

   enclosed 
  between 
  two 
  bands 
  of 
  felsite. 
  It 
  is 
  more 
  distinctly 
  schis- 
  

   tose 
  under 
  the 
  microscope 
  than 
  the 
  last, 
  and 
  the 
  green 
  mineral, 
  

   which 
  is 
  apparently 
  actinolite 
  (see 
  Dr. 
  Patton's 
  note, 
  p. 
  494), 
  is 
  not 
  

   so 
  distinctly 
  acicular, 
  but 
  runs 
  in 
  irregular 
  strings. 
  The 
  felspar 
  

   shows 
  no 
  twinning, 
  and 
  some 
  quartz 
  appears 
  to 
  be. 
  present. 
  We 
  

   have 
  here, 
  as 
  in 
  many 
  of 
  the 
  preceding 
  cases, 
  the 
  combined 
  effect 
  of 
  

   contact 
  and 
  shearing. 
  

  

  Hcematite 
  occurs 
  most 
  frequently 
  in 
  the 
  coarse 
  grey 
  diorite, 
  and 
  

   is 
  usually 
  enclosed 
  in 
  the 
  chlorite 
  formed 
  from 
  hornblende. 
  It 
  is 
  

   often 
  associated 
  with 
  ilmenite 
  and 
  leucoxene 
  in 
  such 
  a 
  way 
  as 
  to 
  

   suggest 
  that 
  it 
  sometimes 
  results 
  from 
  the 
  alteration 
  of 
  the 
  former. 
  

   It 
  appears 
  in 
  bright 
  red 
  blotches 
  or 
  in 
  lath-shaped 
  sections, 
  orien- 
  

   tated 
  with 
  the 
  cleavage 
  of 
  the 
  chlorite 
  or 
  biotite. 
  

  

  Calcite 
  is 
  frequent 
  in 
  altered 
  diorite, 
  and 
  in 
  the 
  schists 
  which 
  

   result 
  from 
  further 
  metamorphic 
  action. 
  It 
  is 
  a 
  decomposition 
  

   product 
  of 
  both 
  hornblende 
  and 
  felspar. 
  

  

  Apatite 
  and 
  Magnetite 
  are 
  often 
  noticed 
  in 
  Mr. 
  Kutley's 
  paper 
  on 
  

  

  * 
  In 
  Uteris. 
  t 
  Brit. 
  Petrogr. 
  p. 
  235. 
  \ 
  Ibid. 
  p. 
  235. 
  

  

  