﻿Yol. 
  53.] 
  GRANITE 
  FROM 
  THE 
  MIDDLE 
  CHALK 
  OF 
  BETCHWORTH. 
  217 
  

  

  felspar 
  are 
  more 
  or 
  less 
  cracked 
  and 
  recemented 
  ; 
  there 
  are 
  some 
  

   strain-shadows 
  in 
  the 
  former, 
  and 
  I 
  am 
  disposed 
  to 
  attribute 
  a 
  

   cross-hatched 
  structure, 
  which 
  occurs 
  ' 
  sporadically 
  ' 
  in 
  the 
  latter, 
  

   to 
  the 
  same 
  cause. 
  The 
  rock, 
  in 
  short, 
  is 
  gneissoid 
  from 
  pressure, 
  

   and 
  resembles 
  those 
  which 
  are 
  rather 
  common 
  in 
  the 
  same 
  regions 
  

   as 
  the 
  last-named. 
  

  

  ' 
  I 
  have 
  compared 
  these 
  slices 
  with 
  one 
  from 
  the 
  original 
  Purley 
  

   boulder 
  given 
  to 
  me 
  by 
  Prof. 
  Judd. 
  In 
  this 
  the 
  felspar 
  is 
  more 
  

   distinctly 
  idiomorphic, 
  the 
  quartz 
  has 
  slightly 
  larger 
  cavities, 
  there 
  

   is 
  hardly 
  any 
  mica 
  (biotite), 
  and 
  one 
  small 
  grain, 
  I 
  think, 
  of 
  horn- 
  

   blende. 
  One 
  or 
  two 
  zircons 
  occur, 
  and 
  also 
  a 
  few 
  very 
  small 
  

  

  Fig. 
  2. 
  — 
  Microscopic 
  section 
  of 
  Boulder 
  B. 
  

  

  X30. 
  

  

  The 
  dark 
  grains 
  are 
  garnets 
  containing 
  much 
  opacite. 
  The 
  clear 
  grains 
  are 
  

   quartz. 
  The 
  white 
  mica 
  can 
  be 
  recognized 
  by 
  its 
  cleavage-lines. 
  The 
  

   rest 
  of 
  the 
  slide 
  is 
  felspar. 
  The 
  rather 
  wavy 
  dusty 
  lines 
  are 
  cracks, 
  stained 
  

   or 
  bordered 
  with 
  decomposition-products. 
  

  

  minerals, 
  probably 
  of 
  secondary 
  origin, 
  together 
  with 
  one 
  slightly 
  

   larger, 
  which 
  is 
  oblong 
  in 
  form 
  ; 
  these 
  I 
  cannot 
  identify 
  with 
  

   certainty, 
  and 
  need 
  not 
  discuss 
  on 
  the 
  present 
  occasion. 
  This 
  rock, 
  

   though 
  less 
  affected 
  by 
  pressure, 
  might 
  have 
  come 
  from 
  the 
  same 
  

   region 
  as 
  the 
  others. 
  I 
  have 
  also 
  compared 
  Mr. 
  Stebbing's 
  

   specimens 
  with 
  a 
  slice 
  from 
  a 
  boulder 
  obtained 
  by 
  Mr. 
  Starkie 
  

   Gardner 
  from 
  the 
  Kentish 
  Gault, 
  which 
  is 
  almost 
  wholly 
  composed 
  

   of 
  quartz 
  and 
  felspar, 
  and 
  is 
  much 
  pressure-modified.' 
  

   Q. 
  J. 
  G. 
  S. 
  No. 
  210. 
  q 
  

  

  