﻿1CR. 
  F. 
  EriLET 
  OS" 
  FTXGrFITFS 
  FE01T 
  SIOSTIE 
  TISO. 
  

  

  3. 
  On 
  FrxGFEiiFS 
  from 
  3Joxff 
  Yiso. 
  By 
  Peaxe; 
  B 
  filet, 
  Esq... 
  

   F.G-.S., 
  Lecturer 
  on 
  Mineralogy 
  in 
  the 
  Boyal 
  School 
  of 
  Mjnafc 
  

   (Eead 
  December 
  5. 
  1SSS.) 
  

  

  [Plate 
  HL] 
  

  

  The 
  specimens 
  described 
  in 
  this 
  paper 
  were 
  collected 
  within 
  six 
  or 
  

   seven 
  feet 
  of 
  the 
  summit 
  of 
  lEonte 
  Yiso 
  (about 
  12,680 
  feet 
  above 
  

   the 
  sea-level) 
  by 
  Mr. 
  .James 
  Bodes, 
  F.G.S., 
  who 
  kindly 
  forwarded 
  

   them 
  to 
  me 
  for 
  examination. 
  

  

  The 
  larger 
  one, 
  fig. 
  1, 
  PI. 
  III., 
  is 
  a 
  piece 
  of 
  compact 
  bluish-grey 
  

   rock, 
  about 
  6| 
  inches 
  long 
  by 
  lj 
  inch 
  in 
  its 
  greatest 
  breadth. 
  In 
  

   one 
  part 
  it 
  shows 
  a 
  delicate 
  banding, 
  the 
  direction 
  of 
  which 
  is 
  in- 
  

   dicated 
  by 
  an 
  arrow, 
  b. 
  placed 
  on 
  the 
  left 
  of 
  the 
  figure. 
  This 
  

   banding, 
  however, 
  is 
  not 
  distinctly 
  visible 
  on 
  the 
  surface 
  represented,- 
  

   although 
  it 
  is 
  well 
  denned 
  on 
  the 
  back 
  of 
  the 
  specimen, 
  which 
  is 
  

   bounded 
  on 
  one 
  side 
  by 
  a 
  smooth 
  joint-plane, 
  c 
  c, 
  upon 
  portions 
  of 
  

   which 
  a 
  thin 
  crust 
  of 
  fulgurite-glass 
  has 
  been 
  formed. 
  The 
  outer 
  

   surfaces 
  are 
  far 
  less 
  even 
  ; 
  but 
  if 
  not 
  actually 
  joint-planes, 
  they 
  have, 
  

   at 
  all 
  events, 
  been 
  directions 
  of 
  easy 
  fission, 
  suggestive 
  of 
  a 
  system 
  of 
  

   intersecting 
  joints, 
  and 
  these, 
  in 
  several 
  parts, 
  are 
  incrusted 
  with 
  

   minute 
  pellets 
  and 
  thin 
  films 
  of 
  fulgurite-glass. 
  

  

  The 
  surface 
  shown 
  in 
  fig. 
  1, 
  PI. 
  IH. 
  (natural 
  size), 
  has 
  been 
  

   ploughed 
  out 
  by 
  lightning, 
  the 
  track 
  being 
  marked 
  by 
  curved 
  and 
  

   branching, 
  hemicylindrical 
  farrows, 
  a 
  a, 
  varying 
  from 
  about 
  -J 
  inch 
  

   to 
  -£% 
  inch 
  in 
  diameter. 
  

  

  These 
  tubes 
  are 
  lined 
  with 
  a 
  thin 
  crust 
  of 
  dark 
  brown, 
  vesicular 
  

   fulgurite-glass, 
  and 
  one 
  of 
  the 
  smallest 
  branches 
  of 
  the 
  longest 
  tube 
  

   is 
  completely 
  filled 
  with 
  this 
  substance. 
  The 
  approximate 
  thickness 
  

   of 
  the 
  glassy 
  lining 
  of 
  part 
  of 
  a 
  tube 
  is 
  shown 
  in 
  fig. 
  2, 
  PI. 
  III., 
  

   while 
  the 
  slaggy 
  and 
  vesicular 
  character 
  of 
  the 
  vitrified 
  surface 
  is 
  

   represented 
  in 
  fig. 
  3, 
  PI. 
  IH., 
  as 
  seen 
  under 
  a 
  very 
  low 
  magnifying 
  - 
  

   power, 
  where 
  a 
  a 
  represents 
  a 
  portion 
  of 
  one 
  of 
  the 
  lightning-tubes 
  

   with 
  its 
  glassy 
  lining 
  : 
  l, 
  a 
  delicate 
  band 
  in 
  the 
  rock 
  due 
  to 
  foliation, 
  

   and 
  / 
  some 
  minute 
  grains 
  of 
  fulgurite-glass 
  adhering 
  to 
  the 
  surface 
  

   of 
  the 
  rock 
  and 
  situated 
  at 
  a 
  slight 
  distance 
  from 
  the 
  left 
  wall 
  of 
  

   the 
  tube. 
  This 
  drawing 
  was 
  made 
  from 
  a 
  specimen 
  considerably 
  

   smaller 
  than 
  the 
  one 
  first 
  described, 
  and 
  it 
  shows 
  only 
  part 
  of 
  a 
  single 
  

   tube 
  having 
  an 
  average 
  diameter 
  of 
  ^ 
  inch. 
  

  

  Before 
  describing 
  the 
  microscopic 
  characters 
  of 
  the 
  fulgurite-glass 
  

   it 
  may 
  be 
  well 
  to 
  give 
  some 
  account 
  of 
  the 
  mineral 
  constitution 
  of 
  

   the 
  rock 
  from 
  which, 
  through 
  fusion, 
  the 
  glass 
  has 
  been 
  formed. 
  

  

  YTien 
  a 
  thin 
  section 
  of 
  this 
  rock 
  is 
  examined 
  under 
  the 
  micro- 
  

   scope, 
  a 
  general 
  schistose 
  and, 
  in 
  places, 
  an 
  almost 
  fibrous-looking 
  

   structure 
  is 
  visible, 
  due 
  to 
  an 
  intimate 
  admixture 
  of 
  glaucophane 
  and 
  

   epidote, 
  the 
  former 
  of 
  a 
  pale 
  blue, 
  the 
  latter 
  of 
  a 
  pale 
  yellowish 
  

   colour. 
  

  

  The 
  glaucophane 
  appears, 
  as 
  a 
  rule, 
  in 
  imperfectly 
  developed 
  

  

  