﻿494 
  DE. 
  C. 
  CALLAWAY 
  ON 
  SECONDARY 
  MINERALS 
  IN 
  THE 
  

  

  tioned 
  properties, 
  we 
  can 
  notice 
  that 
  the 
  axial 
  plane 
  is 
  at 
  right 
  

   angles 
  to 
  the 
  longest 
  axis, 
  and 
  that 
  the 
  extinction 
  is 
  parallel 
  or 
  at 
  

   right 
  angles 
  to 
  the 
  same. 
  The 
  other 
  diorite-bands 
  partake 
  of 
  the 
  

   nature 
  of 
  this 
  sheared 
  portion 
  in 
  that 
  they 
  show 
  much 
  chlorite 
  and 
  

   epidote, 
  the 
  former 
  occasionally 
  interlaminated 
  with 
  black 
  mica." 
  

  

  Identification 
  of 
  the 
  actinolite 
  (?) 
  in 
  the 
  green 
  schist 
  near 
  the 
  

   summit 
  of 
  Ragged 
  Stone 
  Hill: 
  — 
  

  

  " 
  I 
  think 
  this 
  is 
  actinolite 
  on 
  account 
  of 
  the 
  following 
  properties 
  : 
  — 
  

   Pleochroism 
  marked 
  green-yellow, 
  with 
  the 
  least 
  absorption 
  at 
  right 
  

   angles 
  to 
  the 
  longer 
  axis 
  of 
  the 
  crystals. 
  The 
  longer 
  axis 
  is 
  also 
  

   axis 
  of 
  least 
  elasticity. 
  The 
  mineral 
  shows 
  further 
  moderately 
  

   high 
  index 
  of 
  refraction 
  (judging 
  from 
  the 
  roughness 
  of 
  the 
  surface) 
  

   and 
  double 
  refraction." 
  

  

  4. 
  Exogenous 
  Origin 
  of 
  the 
  Granite-veins. 
  

  

  It 
  is 
  of 
  the 
  first 
  importance 
  to 
  determine 
  whether 
  the 
  veins 
  are 
  

   segregatory 
  or 
  intrusive. 
  That 
  they 
  are 
  coarse-grained 
  compounds 
  

   of 
  orthoclase 
  and 
  quartz 
  would 
  rather 
  suggest 
  an 
  endogenous 
  origin 
  ; 
  

   but 
  the 
  following 
  evidence 
  seems 
  to 
  establish 
  their 
  intrusive 
  

   character. 
  

  

  a. 
  They 
  appear 
  as 
  Apophyses 
  from 
  large 
  masses. 
  — 
  We 
  have 
  seen 
  

   that 
  at 
  the 
  southern 
  end 
  of 
  Swinyard's 
  Hill 
  the 
  plexus 
  of 
  veins 
  in 
  

   the 
  shear-zone 
  is 
  in 
  close 
  proximity 
  with 
  the 
  larger 
  veins 
  wdiich 
  

   penetrate 
  the 
  diorite 
  in 
  the 
  unsheared 
  rock 
  above, 
  and 
  these 
  large 
  

   veins 
  are 
  succeeded 
  at 
  a 
  short 
  distance 
  by 
  masses 
  several 
  yards 
  in 
  

   breadth. 
  Man} 
  r 
  smaller 
  veins 
  occur 
  amongst 
  the 
  masses, 
  and 
  both 
  

   veins 
  and 
  masses 
  are 
  occasionally 
  sheared 
  into 
  gneiss. 
  Similar 
  

   granite 
  is 
  found 
  at 
  intervals 
  along 
  the 
  ridge, 
  and 
  towards 
  its 
  nor- 
  

   thern 
  end 
  the 
  granite 
  swells 
  out 
  into 
  a 
  mass 
  extending 
  along 
  the 
  

   axis 
  for 
  several 
  hundred 
  yards. 
  There 
  is 
  no 
  reason 
  for 
  believing 
  

   that 
  the 
  veins 
  have 
  a 
  different 
  origin 
  from 
  the 
  masses, 
  and 
  it 
  is 
  not 
  

   easy 
  to 
  believe 
  that 
  the 
  latter 
  have 
  been 
  formed 
  by 
  segregation. 
  

  

  b. 
  They 
  have 
  the 
  same 
  Texture 
  in 
  different 
  hinds 
  of 
  Diorite. 
  — 
  The 
  

   same 
  granite 
  is 
  found 
  in 
  the 
  two 
  chief 
  kinds 
  of 
  diorite. 
  It 
  is 
  the 
  

   same 
  large-grained 
  binary 
  compound 
  when 
  enclosed 
  in 
  the 
  coarse 
  

   diorite 
  of 
  the 
  North 
  Hill 
  and 
  Worcestershire 
  Beacon 
  as 
  in 
  the 
  fine- 
  

   grained 
  black 
  variety 
  of 
  Wind's 
  Point 
  and 
  Swinyard's 
  Hill. 
  We 
  

   should 
  hardly 
  expect 
  a 
  granite 
  or 
  pegmatite 
  of 
  the 
  same 
  texture 
  to 
  

   be 
  segregated 
  from 
  magmas, 
  one 
  of 
  which 
  is 
  (roughly 
  speaking) 
  

   three 
  times 
  as 
  coarse 
  as 
  the 
  other. 
  

  

  c. 
  They 
  produce 
  Contact-effects 
  similar 
  to 
  those 
  of 
  intrusive 
  Veins. 
  — 
  

   The 
  action 
  of 
  granite-masses 
  on 
  diorite 
  in 
  contact 
  has 
  been 
  described 
  

   by 
  Dr. 
  Ch. 
  Barrois. 
  The 
  following 
  are 
  the 
  chief 
  effects 
  noticed 
  by 
  

   him 
  * 
  : 
  — 
  

  

  (1) 
  Abundance 
  of 
  quartz 
  in 
  large 
  distinct 
  irregular 
  grains. 
  

  

  (2) 
  Much 
  alteration 
  of 
  the 
  crystals 
  of 
  felspar, 
  which 
  are 
  filled 
  

   with 
  quartz-granules, 
  and 
  epigenized 
  by 
  calcite. 
  

  

  * 
  Le 
  Granite 
  de 
  Kostrenen, 
  p. 
  104. 
  

  

  