﻿298 
  Scientific 
  Intelligence. 
  

  

  axis 
  and 
  somewhat 
  faulted. 
  Upon 
  these 
  greatly 
  eroded 
  strata, 
  

   basic 
  breccias 
  were 
  piled 
  up, 
  eroded 
  in 
  turn 
  and 
  then 
  came 
  vast 
  

   flows 
  of 
  rhyolite, 
  which 
  now 
  form 
  part 
  of 
  the 
  Park 
  Plateau 
  and 
  

   hide 
  the 
  northern 
  end 
  of 
  the 
  range. 
  

  

  In 
  the 
  fifth 
  chapter 
  Hague 
  describes 
  the 
  geology 
  of 
  a 
  mountain- 
  

   ous 
  area 
  in 
  the 
  southern 
  part 
  of 
  the 
  Park, 
  which 
  consists 
  of 
  a 
  

   number 
  of 
  ridges 
  of 
  northwest 
  and 
  southeast 
  trend, 
  mostly 
  com- 
  

   posed 
  of 
  Mesozoic 
  rocks. 
  The 
  irregular 
  outline 
  of 
  these 
  mountains 
  

   is 
  due 
  to 
  the 
  rhyolites 
  of 
  the 
  Park 
  Plateau 
  that 
  abut 
  against 
  the 
  

   upturned 
  beds. 
  A 
  few 
  exposures 
  of 
  dacite 
  occur 
  in 
  this 
  area 
  sur- 
  

   rounded 
  by 
  rhyolite 
  which 
  they 
  apparently 
  antedate. 
  Hot 
  spring 
  

   areas 
  and 
  localities 
  of 
  fossil 
  flora 
  are 
  described. 
  An 
  interesting 
  

   and 
  important 
  feature 
  is 
  the 
  discovery 
  of 
  the 
  former 
  outlet 
  of 
  the 
  

   Yellowstone 
  Lake 
  in 
  Outlet 
  Caiion 
  through 
  Chicken 
  Ridge, 
  which 
  

   in 
  former 
  times 
  served 
  to 
  drain 
  the 
  lake 
  waters 
  westward 
  into 
  the 
  

   Snake 
  River 
  and 
  so 
  into 
  the 
  Pacific, 
  instead 
  of 
  into 
  Atlantic 
  

   waters 
  as 
  at 
  present. 
  The 
  chapter 
  closes 
  with 
  a 
  description 
  of 
  

   Two-Ocean 
  Plateau, 
  forming 
  part 
  of 
  the 
  Absaroka 
  Range 
  and 
  

   composed 
  of 
  volcanic 
  breccias 
  and 
  silts. 
  

  

  The 
  southern 
  end 
  of 
  the 
  Snowy 
  Range 
  is 
  described 
  by 
  Weed. 
  

   It 
  forms 
  the 
  northeast 
  corner 
  of 
  the 
  Park 
  and 
  its 
  plateau-like 
  

   summit 
  of 
  crystalline 
  rocks 
  is 
  flanked 
  by 
  Paleozoic 
  sediments 
  

   which 
  dip 
  southward 
  toward 
  the 
  Park. 
  Detailed 
  sections 
  of 
  

   these 
  sediments 
  are 
  given. 
  The 
  highest 
  peaks, 
  as 
  well 
  as 
  con- 
  

   siderable 
  areas, 
  are 
  formed 
  by 
  andesitic 
  breccias 
  lying 
  on 
  the 
  

   Paleozoic 
  rocks. 
  

  

  In 
  Chapter 
  vn, 
  Iddings 
  describes 
  the 
  Miocene 
  volcano 
  of 
  Cran- 
  

   dall 
  basin, 
  which 
  was 
  built 
  up 
  on 
  eroded 
  Paleozoic 
  strata 
  and 
  

   earlier 
  lava 
  flows. 
  It 
  consisted 
  of 
  andesitic 
  breccias 
  topped 
  by 
  

   basalt 
  flows 
  and 
  cut 
  by 
  dikes 
  radiating 
  from 
  the 
  central 
  conduit, 
  

   which 
  was 
  finally 
  filled 
  with 
  magma; 
  this 
  became 
  a 
  mass 
  of 
  

   granular 
  rock 
  varying 
  from 
  gabbro 
  to 
  diorite 
  and 
  in 
  part 
  mon- 
  

   zonite-like 
  in 
  character. 
  In 
  the 
  outer 
  flanks 
  of 
  the 
  great 
  volcano 
  

   the 
  breccias 
  were 
  fine 
  and 
  well-bedded; 
  near 
  the 
  core 
  they 
  are 
  

   coarse 
  and 
  chaotic. 
  Comparison 
  with 
  modern 
  cones 
  of 
  equal 
  size 
  

   like 
  Etna 
  shows 
  the 
  volcano 
  rose 
  over 
  13,000 
  feet 
  above 
  the 
  Pale- 
  

   ozoic 
  floor. 
  It 
  is 
  now 
  thoroughly 
  dissected 
  by 
  erosion 
  and 
  its 
  

   interior 
  laid 
  open. 
  

  

  In 
  the 
  four 
  following 
  chapters 
  Iddings 
  describes 
  the 
  petrography 
  

   of 
  the 
  types 
  of 
  igneous 
  rocks 
  found 
  in 
  the 
  Park, 
  the 
  various 
  

   kinds 
  of 
  andesites 
  and 
  andesitic 
  breccias 
  that 
  so 
  largely 
  make 
  up 
  

   the 
  Absaroka 
  Range, 
  the 
  rhyolites 
  which 
  compose 
  the 
  great 
  

   plateau, 
  the 
  basalts 
  and 
  certain 
  rocks 
  of 
  peculiar 
  composition 
  

   found 
  as 
  dikes 
  and 
  small 
  flows 
  and 
  classified 
  as 
  absarokites, 
  bana- 
  

   tites 
  and 
  shoshonites. 
  These 
  descriptions 
  include 
  in 
  essence 
  the 
  

   former 
  memoirs 
  of 
  the 
  author 
  on 
  the 
  rhyolite 
  and 
  glass 
  of 
  

   Obsidian 
  Cliff 
  (7th 
  Ann. 
  Rep. 
  U. 
  S. 
  Geol. 
  Surv., 
  1888, 
  pp. 
  249- 
  

   295) 
  and 
  on 
  the 
  peculiar 
  dikes 
  and 
  flows 
  (Jour, 
  of 
  Geol., 
  1895, 
  

   p. 
  935). 
  

  

  