﻿J. 
  S. 
  Diller 
  — 
  Grater 
  Lake, 
  Oregon. 
  171 
  

  

  consequent 
  collapse 
  of 
  the 
  floor 
  of 
  the 
  pit 
  with 
  portions 
  of 
  the 
  

   surrounding 
  cliffs, 
  are 
  shown 
  to 
  result 
  from 
  the 
  escape 
  of 
  the 
  

   lava 
  through 
  fissures 
  at 
  much 
  lower 
  levels 
  upon 
  the 
  slope 
  of 
  

   the 
  mountain. 
  In 
  connection 
  with 
  the 
  subsidence 
  of 
  the 
  lava 
  

   in 
  Kilauea 
  in 
  1840 
  a 
  mass 
  was 
  erupted 
  27 
  miles 
  from 
  Kilauea 
  

   and 
  about 
  2700 
  feet 
  below 
  the 
  summit 
  of 
  its 
  cliff. 
  In 
  some 
  

   cases, 
  however, 
  the 
  sinking 
  of 
  the 
  lava 
  in 
  Kilauea 
  is 
  not 
  known 
  

   to 
  have 
  been 
  accompanied 
  by 
  an 
  eruption 
  of 
  lava 
  upon 
  the 
  

   surface. 
  

  

  The 
  view 
  that 
  the 
  caldera 
  of 
  Crater 
  Lake 
  originated 
  by 
  sub- 
  

   sidence 
  appears 
  especially 
  applicable 
  for 
  the 
  reason 
  that 
  it 
  

   occurs 
  in 
  the 
  summit 
  of 
  a 
  prominent 
  range. 
  The 
  western 
  

   slope 
  of 
  the 
  range, 
  although 
  not 
  steep, 
  is 
  considerably 
  more 
  

   inclined 
  than 
  that 
  of 
  Kilauea; 
  and 
  within 
  15 
  miles 
  of 
  the 
  lake, 
  

   the 
  level 
  of 
  its 
  deepest 
  bed 
  appears 
  upon 
  the 
  surface. 
  The 
  

   engulfment 
  of 
  Mt. 
  Mazama 
  and 
  the 
  production 
  of 
  such 
  an 
  

   enormous 
  pit 
  in 
  the 
  process 
  may 
  well 
  be 
  expected 
  to 
  have 
  

   given 
  rise 
  to 
  eruptions 
  upon 
  the 
  lower 
  slopes 
  of 
  the 
  range 
  at 
  

   no 
  very 
  great 
  distance 
  from 
  the 
  lake. 
  

  

  That 
  Mt. 
  Mazama 
  actually 
  disappeared 
  by 
  subsidence 
  is 
  

   plainly 
  suggested 
  by 
  the 
  behavior 
  of 
  the 
  last 
  erupted 
  lava. 
  It 
  

   is 
  a 
  rhyolite 
  which 
  escaped 
  from 
  the 
  north 
  slope 
  of 
  Mt. 
  

   Mazama. 
  Its 
  broad 
  stream 
  follows 
  a 
  shallow 
  valley 
  that 
  now 
  

   appears 
  in 
  the 
  rim 
  at 
  the 
  head 
  of 
  Cleetwood 
  Cove. 
  Upon 
  the 
  

   outer 
  slope 
  of 
  the 
  rim, 
  opposite 
  the 
  cove, 
  there 
  is 
  a 
  long 
  depres- 
  

   sion 
  down 
  the 
  surface 
  of 
  the 
  flow 
  where 
  cliffs, 
  columns 
  and 
  

   angular 
  blocks 
  occur 
  in 
  great 
  confusion. 
  They 
  have 
  resulted 
  

   from 
  the 
  caving 
  in 
  of 
  the 
  crust 
  of 
  the 
  lava 
  tunnel 
  in 
  the 
  val- 
  

   ley 
  filled 
  by 
  the 
  thickest 
  portion 
  of 
  the 
  flow. 
  But 
  on 
  both 
  

   sides 
  the 
  lava 
  surface 
  is 
  smooth 
  and 
  easily 
  traversed. 
  

  

  Upon 
  the 
  inner 
  slope 
  of 
  the 
  rim 
  is 
  an 
  equally 
  remarkable 
  

   and 
  exceptional 
  feature. 
  Descending 
  from 
  the 
  Rugged 
  Crest, 
  

   at 
  the 
  upper 
  end 
  of 
  the 
  broken 
  tunnel, 
  to 
  the 
  lake 
  is 
  a 
  flow 
  

   several 
  hundred 
  yards 
  in 
  width. 
  It 
  is 
  part 
  of 
  the 
  large 
  stream 
  

   of 
  rhyolite 
  which 
  spread 
  upon 
  the 
  outer 
  slope 
  of 
  the 
  rim, 
  and 
  

   has 
  flowed 
  inwards 
  towards 
  the 
  lake 
  over 
  the 
  broken 
  ends 
  of 
  

   the 
  older 
  coulees 
  of 
  andesite. 
  The 
  fluidal 
  structure, 
  as 
  well 
  as 
  

   the 
  parting 
  planes 
  produced 
  by 
  it, 
  are 
  well 
  marked 
  approxi- 
  

   mately 
  parallel 
  to 
  the 
  inner 
  slope 
  of 
  the 
  rim. 
  It 
  is 
  the 
  only 
  

   inward-flowing 
  lava 
  found 
  anywhere 
  on 
  the 
  rim, 
  and 
  appears 
  

   to 
  indicate 
  that 
  before 
  the 
  thickest 
  portion 
  of 
  the 
  final 
  flow 
  of 
  

   rhyolite 
  had 
  completely 
  solidified, 
  Mt. 
  Mazama 
  was 
  engulfed, 
  

   and 
  the 
  yet 
  viscous 
  lava 
  followed 
  it 
  towards 
  the 
  abyss. 
  

  

  It 
  might 
  be 
  supposed 
  that 
  a 
  study 
  of 
  the 
  features 
  upon 
  the 
  

   bottom 
  of 
  the 
  great 
  pit 
  would 
  disclose 
  the 
  character 
  of 
  the 
  

   change 
  by 
  which 
  it 
  was 
  produced 
  ; 
  but 
  this 
  is 
  not 
  the 
  case. 
  

   Its 
  original 
  surface 
  is 
  in 
  large 
  part, 
  if 
  not 
  wholly, 
  covered 
  by 
  

  

  