﻿Iddings 
  and 
  Penfield 
  — 
  Spherulites 
  from 
  Wyoming. 
  39 
  

  

  Art. 
  Y. 
  — 
  The 
  Minerals 
  in 
  hollow 
  Spherulites 
  of 
  Rhyolite 
  

   from 
  Glade 
  Creek, 
  Wyoming 
  • 
  by 
  J. 
  P. 
  Iddings 
  and 
  S. 
  L. 
  

  

  Penfield. 
  

  

  The 
  occurrence 
  of 
  fayalite 
  with 
  quartz, 
  tridymite 
  and 
  soda- 
  

   orthoclase 
  or 
  sanidine 
  in 
  the 
  lithophysse 
  and 
  hollow 
  spherulites 
  

   of 
  the 
  obsidian 
  at 
  Obsidian 
  Cliff, 
  Yellowstone 
  National 
  Park,* 
  has 
  

   been 
  described 
  by 
  one 
  of 
  the 
  writers 
  of 
  the 
  present 
  paper, 
  the 
  

   mineralogical 
  investigation 
  of 
  the 
  fayalite 
  and 
  sanidine 
  having 
  

   been 
  carried 
  on 
  by 
  the 
  other 
  writer. 
  Recently 
  we 
  have 
  had 
  

   occasion 
  to 
  call 
  attention 
  to 
  the 
  occurrence 
  of 
  fayalite 
  in 
  obsid- 
  

   ian 
  at 
  Lipari 
  and 
  Yulcano 
  in 
  the 
  Mediterranean, 
  f 
  and 
  have 
  

   observed 
  that 
  the 
  modes 
  of 
  occurrence 
  are 
  alike 
  in 
  both 
  regions, 
  

   and 
  that 
  the 
  causes 
  leading 
  to 
  the 
  crystallization 
  of 
  fayalite 
  in 
  

   these 
  magmas 
  must 
  have 
  been 
  the 
  same, 
  namely 
  : 
  the 
  action 
  of 
  

   superheated 
  vapors, 
  presumably 
  of 
  water, 
  upon 
  the 
  magmas 
  

   before 
  their 
  final 
  consolidation 
  and 
  cooling. 
  

  

  In 
  the 
  present 
  paper 
  we 
  wish 
  to 
  contribute 
  further 
  to 
  the 
  

   knowledge 
  of 
  these 
  aqueo-igneous 
  products 
  in 
  siliceous 
  lavas, 
  by 
  

   describing 
  a 
  somewhat 
  different 
  development 
  of 
  hollow 
  spheru- 
  

   lites 
  in 
  rhyolite 
  at 
  the 
  forks 
  of 
  Glade 
  Creek, 
  a 
  tributary 
  of 
  the 
  

   Snake 
  River, 
  just 
  south 
  of 
  the 
  boundary 
  of 
  the 
  Yellowstone 
  

   National 
  Park. 
  This 
  locality 
  was 
  visited 
  by 
  us 
  in 
  the 
  sum- 
  

   mer 
  of 
  1886. 
  The 
  rhyolite 
  forms 
  a 
  high 
  bluff 
  of 
  massive 
  

   rock, 
  exhibiting 
  great 
  contortion 
  of 
  banding 
  or 
  planes 
  of 
  flow. 
  

   The 
  spur 
  between 
  the 
  two 
  branches 
  of 
  the 
  stream 
  rises 
  some 
  

   1200 
  feet 
  above 
  the 
  valley, 
  and 
  presents 
  a 
  section 
  of 
  the 
  great 
  

   rhyolite 
  sheet 
  which 
  forms 
  the 
  mass 
  of 
  Pitchstone 
  Plateau, 
  

   lying 
  to 
  the 
  north. 
  

  

  The 
  rock 
  at 
  the 
  forks 
  of 
  Glade 
  Creek 
  is 
  dark 
  gray, 
  dull, 
  

   lusterless 
  and 
  lithoidal, 
  with 
  a 
  rough 
  hackly 
  fracture. 
  It 
  

   carries 
  many 
  phenocrysts 
  of 
  a 
  white 
  plagioclase, 
  less 
  numer- 
  

   ous 
  glassy 
  sanidines 
  and 
  quartzes, 
  and 
  many 
  rusted 
  crystals, 
  

   which 
  prove 
  to 
  be 
  more 
  or 
  less 
  altered 
  augites. 
  Through 
  this 
  

   mass 
  are 
  scattered 
  cavities 
  with 
  light 
  gray 
  or 
  white 
  walls, 
  

   which 
  are 
  partially 
  filled 
  with 
  crystals. 
  The 
  cavities 
  vary 
  in 
  

   size 
  from 
  that 
  of 
  a 
  walnut 
  to 
  almost 
  nothing. 
  They 
  are 
  irregu- 
  

   lar 
  in 
  shape, 
  but 
  the 
  spherical 
  form 
  of 
  the 
  light 
  colored 
  walls 
  

   suggests 
  at 
  once 
  that 
  they 
  are 
  the 
  cavities 
  of 
  very 
  hollow 
  

   spherulites. 
  They 
  are, 
  in 
  fact, 
  wide-gaping 
  spherulites 
  like 
  

   some 
  of 
  those 
  found 
  at 
  Obsidian 
  Cliff.J 
  Occasionally 
  there 
  are 
  

  

  *J. 
  P. 
  Iddings, 
  Obsidian 
  Cliff, 
  Yellowstone 
  National 
  Park, 
  Seventh 
  Annual 
  

   Report 
  of 
  the 
  Director 
  of 
  the 
  U. 
  S. 
  Geological 
  Survey, 
  Washington, 
  1888. 
  

  

  f 
  Iddings 
  and 
  Penfield, 
  .Fayalite 
  in 
  the 
  obsidian 
  of 
  Lipari. 
  This 
  Journal, 
  vol. 
  

   xl, 
  July, 
  1890. 
  

  

  \ 
  1. 
  c. 
  p. 
  264, 
  and 
  Plate 
  XII, 
  figs. 
  1 
  and 
  5. 
  

  

  