﻿Weed 
  and 
  Pirsson 
  — 
  /Sulphur, 
  Orpiment, 
  Realgar, 
  etc. 
  401 
  

  

  for 
  there 
  is 
  no 
  evidence 
  of 
  volcanism 
  or 
  any 
  similar 
  phenomena 
  

   associated 
  with 
  their 
  silicification. 
  The 
  silica 
  in 
  the 
  eastern 
  

   locality 
  must 
  be 
  sought 
  in 
  the 
  accompanying 
  sand 
  beds 
  and 
  

   was 
  probably 
  brought 
  into 
  solution 
  by 
  the 
  action 
  upon 
  it 
  of 
  

   organic 
  acids. 
  

  

  The 
  study 
  of 
  the 
  Arkansas 
  Tertiary 
  silicified 
  woods 
  appears 
  

   to 
  justify 
  the 
  following 
  conclusions: 
  

  

  1. 
  The 
  silicified 
  woods 
  of 
  eastern 
  Arkansas 
  are 
  all 
  of 
  Ter- 
  

   tiary 
  age. 
  

  

  2. 
  They 
  are 
  derived 
  from 
  the 
  beds 
  of 
  Eocene 
  clays 
  that 
  

   underlie 
  the 
  sands 
  and 
  gravels 
  in 
  which 
  they 
  commonly 
  occur. 
  

  

  3. 
  They 
  are 
  silicified 
  lignite 
  ; 
  the 
  process 
  of 
  silicification 
  has 
  

   occurred 
  either 
  while 
  they 
  were 
  still 
  in 
  clays 
  or 
  most 
  often 
  

   after 
  they 
  were 
  removed 
  and 
  buried 
  in 
  the 
  sands 
  or 
  gravels. 
  

  

  4. 
  They 
  possess 
  as 
  yet 
  no 
  taxonomic 
  value 
  in 
  determining 
  

   the 
  relative 
  ages 
  of 
  the 
  members 
  of 
  the 
  Tertiary 
  series. 
  

  

  Geological 
  Survey, 
  Little 
  Rock, 
  Ark., 
  July 
  15, 
  1891. 
  

  

  Art. 
  XLI. 
  — 
  Occurrence 
  of 
  Sulphur, 
  Orpiment 
  and 
  Realgar 
  

   in 
  the 
  Yellowstone 
  National 
  Park 
  ; 
  by 
  Walter 
  H. 
  Weed 
  

   and 
  Louis 
  Y. 
  Pirsson. 
  

  

  Sulphur. 
  

  

  In 
  the 
  Yellowstone 
  National 
  Park 
  there 
  are 
  besides 
  the 
  well 
  

   known 
  geyser 
  basins, 
  many 
  small 
  hot 
  spring 
  areas 
  and 
  localities 
  

   where 
  fumeroles 
  and 
  solfataras 
  are 
  still 
  active. 
  At 
  most 
  of 
  these 
  

   places 
  deposits 
  of 
  sulphur 
  occur, 
  in 
  and 
  around 
  the 
  vents 
  from 
  

   which 
  sulphurous 
  vapors 
  issue. 
  At 
  the 
  Highland 
  Hot 
  Springs 
  

   and 
  at 
  Crater 
  Hills 
  these 
  vents 
  are 
  quite 
  abundant 
  and 
  large 
  

   deposits 
  of 
  sulphur 
  are 
  found 
  frequently 
  having 
  most 
  beautiful 
  

   clusters 
  of 
  delicate 
  crystals. 
  The 
  latter 
  locality, 
  from 
  which 
  

   the 
  specimens 
  herein 
  described 
  were 
  obtained, 
  is 
  a 
  small 
  group 
  

   of 
  hills 
  whose 
  white 
  and 
  steaming 
  slopes 
  form 
  a 
  prominent 
  

   feature 
  of 
  the 
  eastern 
  part 
  of 
  Hayden 
  Yalley, 
  the 
  open 
  grassy 
  

   country 
  traversed 
  en 
  route 
  from 
  the 
  Grand 
  Canyon 
  of 
  the 
  

   Yellowstone 
  to 
  the 
  Lake 
  or 
  the 
  Firehole 
  geysers. 
  The 
  hills, 
  

   often 
  called 
  Sulphur 
  Mountain, 
  rise 
  about 
  150 
  feet 
  above 
  the 
  

   surrounding 
  level, 
  and 
  are 
  formed 
  of 
  fragmentary 
  material 
  

   wholly 
  rhyolitic, 
  decomposed 
  and 
  cemented 
  by 
  the 
  vapors 
  that 
  

   rise 
  at 
  innumerable 
  points 
  through 
  the 
  hills. 
  There 
  are 
  but 
  

   few 
  springs 
  at 
  this 
  locality; 
  the 
  most 
  prominent 
  and 
  most 
  

   active 
  is 
  an 
  ever-splashing 
  bowl 
  of 
  green 
  sulphurous 
  waters 
  

   known 
  as 
  the 
  Chrome 
  Spring. 
  Behind 
  this 
  basin 
  the 
  slopes 
  

   are 
  light 
  colored, 
  chalky 
  white, 
  rose-pink 
  and 
  dull 
  yellows 
  

  

  