﻿Ob 
  ME. 
  F. 
  EUTLET 
  ON 
  ETJLGTTEITES 
  EEOM 
  MONTE 
  VISO. 
  

  

  cases 
  ; 
  but, 
  be 
  this 
  as 
  it 
  may, 
  these 
  bodies 
  appear, 
  unquestionably, 
  

   to 
  have 
  been 
  formed 
  during 
  the 
  refrigeration 
  of 
  the 
  fulgurite, 
  the 
  

   glass 
  presenting 
  none 
  of 
  the 
  signs 
  which 
  would 
  characterize 
  a 
  

   subsequent 
  devitrification 
  or 
  secondary 
  change. 
  It 
  must 
  be 
  

   confessed, 
  however, 
  that 
  we 
  know 
  as 
  yet 
  nothing 
  of 
  the 
  manner 
  in 
  

   which 
  fulgurite-glasses 
  would 
  undergo 
  devitrification 
  ; 
  but, 
  judging 
  

   from 
  the 
  mineral 
  constitution 
  of 
  this 
  rock, 
  it 
  is 
  possible 
  that 
  we 
  

   might 
  look 
  for 
  somewhat 
  similar 
  changes 
  in 
  a 
  tachylyte. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  in. 
  

  

  Fig. 
  1. 
  Specimen 
  of 
  glaucophane-epidote 
  schist, 
  containing 
  garnet, 
  altered 
  

   sphene, 
  and 
  occasionally 
  a 
  little 
  diallage, 
  from 
  Monte 
  Viso, 
  Cottian 
  

   Alps. 
  aa. 
  Lightning-tubes 
  split 
  open 
  along 
  a 
  joint-plane 
  or 
  uneven 
  

   plane 
  of 
  easy 
  fission. 
  The 
  tubes 
  are 
  lined 
  with 
  a 
  dark-brown 
  glass. 
  

   b. 
  Arrow 
  indicating 
  the 
  general 
  direction 
  of 
  banding 
  or 
  foliation 
  in 
  

   the 
  specimen, 
  cc. 
  Trace 
  of 
  a 
  smooth 
  joint-surface. 
  Natural 
  size. 
  

  

  2. 
  Section 
  of 
  part 
  of 
  a 
  lightning-tube, 
  showing 
  approximate 
  thickness 
  of 
  

  

  the 
  glassy 
  lining. 
  Natural 
  size. 
  

  

  3. 
  aa. 
  Portion 
  of 
  a 
  lightning-tube, 
  showing 
  the 
  slaggy, 
  vesicular 
  character 
  

  

  of 
  the 
  vitreous 
  lining, 
  b. 
  Narrow 
  band, 
  due 
  to 
  foliation 
  and 
  lying 
  

   in 
  a 
  direction 
  approximately 
  at 
  right 
  angles 
  to 
  that 
  of 
  the 
  lightning- 
  

   tube. 
  /. 
  Minute 
  pellets 
  of 
  vitreous 
  matter 
  adhering 
  to 
  the 
  rock, 
  and 
  

   situated 
  not 
  far 
  from 
  the 
  wall 
  of 
  the 
  tube. 
  X 
  between 
  2 
  and 
  3 
  dia- 
  

   meters. 
  

  

  4. 
  Fragment 
  of 
  fulgurite-glass, 
  containing 
  globulites 
  and 
  longulites. 
  

  

  X 
  250 
  linear. 
  

  

  5. 
  Margarites 
  selected 
  from 
  different 
  fragments 
  of 
  fulgurite-glass 
  in 
  which 
  

  

  they 
  occur. 
  X 
  570 
  linear. 
  

  

  6. 
  Fragment 
  of 
  vesicular 
  fulgurite-glass, 
  broken 
  from 
  the 
  lining 
  of 
  one 
  of 
  

  

  the 
  lightning-tubes. 
  X 
  120 
  linear. 
  

  

  7. 
  Doubly 
  refracting 
  microlith 
  in 
  fulgurite-glass. 
  (Oblique 
  extinction 
  

  

  between 
  15° 
  and 
  17° 
  from 
  the 
  longest 
  axis.) 
  X 
  570 
  linear. 
  

  

  8. 
  a 
  and 
  b. 
  Groups 
  of 
  globulites 
  occurring 
  in 
  a 
  section 
  of 
  fulgurite-glass 
  r 
  

  

  X 
  570 
  linear. 
  

  

  Discussion. 
  

  

  Mr. 
  Eccles 
  agreed 
  with 
  the 
  Author's 
  observations 
  concerning 
  the 
  

   mode 
  of 
  production 
  of 
  the 
  tubes, 
  which 
  were 
  produced 
  at 
  the 
  same 
  

   time 
  that 
  the 
  two 
  surfaces 
  were 
  sundered. 
  As 
  regards 
  the 
  absence 
  

   of 
  glass 
  in 
  parts 
  of 
  the 
  tubes, 
  he 
  considered 
  it 
  might 
  be 
  due 
  to 
  

   weathering. 
  

  

  