﻿628 
  ME. 
  F. 
  ETTTLEY 
  ON 
  TACHTLZTE 
  EEOM 
  

  

  what 
  must 
  once 
  have 
  been 
  an 
  almost 
  purely 
  vitreous 
  band 
  (indicated 
  

   by 
  the 
  letter 
  b), 
  which 
  has, 
  however, 
  undergone 
  a 
  partial 
  devitrifi- 
  

   cation, 
  seemingly 
  by 
  the 
  development 
  of 
  globulites. 
  Fluxion-struc- 
  

   ture 
  is 
  very 
  well 
  defined 
  in 
  places. 
  There 
  are 
  a 
  few 
  isolated 
  sphe- 
  

   rules 
  in 
  this 
  band, 
  and 
  between 
  it 
  and 
  the 
  more 
  densely 
  spherulitic 
  

   zone 
  there 
  is 
  a 
  sharp, 
  but 
  very 
  irregular, 
  sinuous 
  line 
  of 
  demarcation 
  

   slightly 
  stained 
  by 
  ferric 
  oxide. 
  The 
  band 
  (b) 
  appears 
  very 
  dark 
  

   between 
  crossed 
  nicols, 
  in 
  spite 
  of 
  the 
  devitrification, 
  showing 
  that 
  

   a 
  considerable 
  amount 
  of 
  unaltered 
  glass 
  is 
  still 
  present. 
  

  

  This 
  band 
  is 
  succeeded 
  by 
  another 
  (indicated 
  by 
  the 
  letter 
  c), 
  

   which 
  is 
  also 
  vitreous 
  in 
  character, 
  and 
  is 
  densely 
  crowded 
  with 
  

   minute, 
  opaque, 
  white 
  specks, 
  which 
  cause 
  it 
  to 
  assume 
  a 
  bluish- 
  

   white 
  milky 
  appearance 
  when 
  viewed 
  in 
  reflected 
  light. 
  When 
  

   thus 
  illuminated 
  the 
  belt 
  is 
  seen 
  to 
  be 
  marked 
  with 
  irregular 
  snow- 
  

   white 
  streaks, 
  indicative 
  of 
  fluxion. 
  

  

  In 
  transmitted 
  light 
  the 
  belt 
  appears 
  of 
  a 
  yellowish-brown 
  to 
  

   reddish-brown 
  or 
  almost 
  coffee-colour, 
  while 
  the 
  fluxion-banding 
  now 
  

   stands 
  out 
  in 
  dark, 
  almost 
  black, 
  streaks. 
  The 
  difference 
  in 
  colour 
  

   between 
  this 
  and 
  the 
  adjacent, 
  nearly 
  colourless 
  band 
  (6) 
  is 
  very 
  

   marked. 
  

  

  In 
  the 
  coffee-coloured 
  band 
  (c) 
  a 
  few 
  well-defined 
  spherules 
  also 
  

   occur. 
  

  

  Between 
  this 
  and 
  the 
  Carboniferous 
  shale 
  there 
  is 
  a 
  very 
  per- 
  

   sistent, 
  irregular, 
  finely 
  crumpled, 
  opaque 
  line 
  of 
  a 
  pale 
  yellowish 
  

   or 
  reddish 
  white. 
  This 
  line 
  represents 
  what 
  appears 
  to 
  be 
  the 
  limit 
  

   of 
  fusion 
  of 
  the 
  shale. 
  

  

  The 
  bands 
  b 
  and 
  c 
  show 
  great 
  irregularity 
  in 
  their 
  respective 
  

   thicknesses, 
  and 
  occasionally 
  one 
  of 
  them 
  seems 
  to 
  thin 
  out 
  almost 
  

   entirely. 
  This 
  is 
  evidently 
  due 
  to 
  the 
  drag 
  exerted 
  upon 
  the 
  once 
  

   viscous 
  matter 
  of 
  the 
  vein 
  by 
  the 
  walls 
  along 
  which 
  it 
  crept, 
  such 
  

   a 
  motion, 
  and 
  that 
  an 
  occasionally 
  retarded 
  one, 
  being 
  sufficiently 
  

   evinced 
  by 
  the 
  fluxion-banding. 
  

  

  To 
  ascertain 
  the 
  relative 
  fusibilities 
  of 
  the 
  whin 
  and 
  the 
  shale 
  two 
  

   small 
  splinters 
  were 
  taken, 
  one 
  of 
  whin 
  and 
  the 
  other 
  of 
  shale, 
  as 
  

   nearly 
  as 
  possible 
  of 
  the 
  same 
  size 
  and 
  thickness, 
  and 
  were 
  held 
  side 
  

   by 
  side 
  in 
  the 
  forceps 
  and 
  exposed 
  to 
  the 
  blowpipe-flame 
  for 
  the 
  

   same 
  period 
  and 
  in 
  the 
  same 
  part 
  of 
  the 
  flame. 
  An 
  exposure 
  of 
  

   several 
  seconds 
  sufficed 
  to 
  fuse 
  the 
  extremity 
  of 
  the 
  fragment 
  of 
  

   whin 
  to 
  a 
  dark 
  glass, 
  while 
  that 
  of 
  the 
  shale 
  was 
  slightly 
  fritted 
  to 
  

   a 
  greyish 
  enamel. 
  

  

  A 
  further 
  exposure 
  to 
  the 
  flame 
  resulted 
  in 
  the 
  formation 
  of 
  more 
  

   and 
  of 
  a 
  darker 
  glass 
  on 
  the 
  shale 
  than 
  that 
  previously 
  developed 
  ; 
  

   but 
  it 
  was 
  at 
  once 
  evident 
  that, 
  of 
  the 
  two 
  splinters, 
  the 
  whin 
  

   produced 
  the 
  darker 
  glass, 
  and 
  was 
  the 
  more 
  readily 
  fusible 
  rock. 
  

   The 
  dark 
  colour 
  of 
  the 
  glass 
  produced 
  by 
  the 
  fusion 
  of 
  the 
  whin 
  in 
  

   the 
  blowpipe-flame 
  is 
  evidently 
  due 
  to 
  further 
  oxidation 
  of 
  the 
  iron 
  

   present 
  in 
  the 
  rock, 
  and 
  which, 
  as 
  shown 
  by 
  the 
  analysis, 
  exists 
  

   chiefly 
  in 
  the 
  condition 
  of 
  protoxide. 
  

  

  The 
  deep 
  colour 
  of 
  the 
  vitreous 
  band 
  in 
  contact 
  with 
  the 
  shale 
  and 
  

   the 
  colourless 
  character 
  of 
  the 
  adjacent 
  glassy 
  one, 
  which 
  unques- 
  

  

  