﻿402 
  Weed 
  and 
  Pirsson 
  — 
  Sulphur, 
  Orpirnent 
  and 
  

  

  being 
  the 
  predominant 
  tints 
  Large 
  masses 
  of 
  rough 
  clinker- 
  

   like 
  rock 
  lie 
  scattered 
  about 
  the 
  slopes, 
  resting 
  upon 
  small 
  

   pieces 
  of 
  the 
  same 
  cemented 
  material 
  or 
  upon 
  the 
  smoother 
  

   slope 
  of 
  white 
  pulverulent 
  silica 
  resulting 
  from 
  the 
  complete 
  

   decomposition 
  of 
  the 
  rh 
  volitic 
  material 
  by 
  the 
  acid 
  waters 
  and 
  

   vapors 
  

  

  Several 
  parts 
  of 
  the 
  slopes 
  show 
  the 
  dull 
  yellow 
  color 
  of 
  sul- 
  

   phur, 
  such 
  places 
  usually 
  being 
  further 
  marked 
  by 
  many 
  steam- 
  

   ing 
  orifices 
  a 
  few 
  inches 
  across. 
  These 
  vents 
  are 
  generally 
  

   lined 
  with 
  a 
  layer 
  of 
  radially 
  fibrous 
  sulphur, 
  whose 
  surface 
  is 
  

   thickly 
  set 
  with 
  delicate 
  frost-like 
  clusters 
  of 
  crystals. 
  Many 
  

   of 
  the 
  vents 
  are 
  partly 
  closed 
  by 
  the 
  sulphur 
  and 
  others 
  com- 
  

   pletely 
  sealed 
  but 
  filled 
  with 
  hot 
  vapor 
  which 
  is 
  copiously 
  

   emitted 
  when 
  the 
  roof 
  is 
  broken. 
  No 
  temperatures 
  above 
  200° 
  

   F. 
  were 
  obtained 
  from 
  any 
  of 
  the 
  vents. 
  It 
  is 
  in 
  these 
  closed 
  

   vents 
  that 
  the 
  largest 
  and 
  most 
  beautiful 
  crystal 
  clusters 
  have 
  

   been 
  found. 
  Upon 
  taking 
  such 
  a 
  specimen 
  from 
  one 
  of 
  these 
  

   vents 
  it 
  is 
  a 
  deep 
  orange 
  tint, 
  and 
  of 
  course 
  quite 
  hot 
  ; 
  as 
  it 
  

   cools 
  the 
  crystals 
  loosen 
  with 
  a 
  loud 
  and 
  continuous 
  crackling 
  

   so 
  that 
  a 
  slight 
  jar 
  is 
  sufficient 
  to 
  cause 
  many 
  of 
  the 
  clusters 
  to 
  

   fall 
  to 
  pieces 
  when 
  cooled. 
  These 
  crystal 
  clusters 
  are 
  of 
  

   interest 
  as 
  sulphur 
  in 
  the 
  crystal 
  form 
  has 
  been 
  described 
  from 
  

   but 
  one 
  American 
  locality 
  — 
  Nevada.* 
  In 
  examining 
  a 
  mass 
  of 
  

   these 
  crystals 
  it 
  is 
  seen 
  that 
  the 
  crystalline 
  mass 
  is 
  of 
  great 
  

   brittleness, 
  owing 
  largely 
  to 
  the 
  fact 
  that 
  the 
  crystals 
  are 
  gen- 
  

   erally 
  hollow. 
  Often 
  a 
  mere 
  skeleton 
  of 
  what 
  would 
  otherwise 
  

   be 
  a 
  good 
  sized 
  crystal 
  is 
  present. 
  One 
  that 
  would 
  be 
  an 
  inch 
  

   high 
  and 
  proportionately 
  broad 
  and 
  wide 
  consists 
  only 
  of 
  nar- 
  

   row 
  strips 
  preserving 
  the 
  edges 
  of 
  the 
  pyramids 
  on 
  each 
  other 
  ; 
  

   this 
  frame 
  work 
  is 
  then 
  filled 
  with 
  other 
  crystals 
  and 
  parallel 
  

   growths, 
  also 
  of 
  hollow 
  delicate 
  material. 
  In 
  general 
  the 
  mass 
  

   is 
  made 
  up 
  of 
  confused 
  crystal 
  aggregates 
  closely 
  united 
  below 
  

   and 
  toward 
  the 
  top 
  branching 
  into 
  arborescent 
  forms. 
  Often 
  

   small 
  solid 
  crystals 
  occur 
  attached 
  to 
  the 
  mass. 
  Several 
  of 
  

   these 
  were 
  selected 
  for 
  measurement. 
  They 
  

   proved 
  to 
  be 
  of 
  the 
  usual 
  orthorhombic 
  sym- 
  

   metry. 
  The 
  habit 
  is 
  strongly 
  pyramidal. 
  One 
  

   of 
  them 
  that 
  is 
  typical 
  of 
  the 
  series 
  is 
  shown 
  in 
  

   the 
  figure. 
  The 
  forms 
  which 
  were 
  identified 
  on 
  

   this 
  crystal 
  are 
  : 
  

  

  c, 
  001,0. 
  e, 
  101,1-1. 
  y, 
  112, 
  i. 
  x, 
  133, 
  1-3. 
  

  

  ra, 
  110, 
  I. 
  n, 
  011, 
  14. 
  s, 
  113, 
  £. 
  q, 
  131, 
  3-3. 
  

  

  h, 
  130, 
  i-3. 
  p, 
  111, 
  1. 
  t, 
  115, 
  |. 
  

  

  The 
  identification 
  of 
  these 
  forms 
  is 
  shown 
  by 
  

   the 
  following 
  tables 
  of 
  calculated 
  and 
  measured 
  angles. 
  For 
  

  

  * 
  E. 
  S. 
  Dana, 
  this 
  Journal, 
  xxxii, 
  p. 
  389, 
  1880. 
  

  

  