﻿170 
  J. 
  S. 
  Diller 
  — 
  Crater 
  Lake, 
  Oregon. 
  

  

  remnants 
  renders 
  it 
  necessary 
  to 
  suppose 
  that 
  it 
  was 
  either 
  

   blown 
  out 
  by 
  a 
  tremendous 
  volcanic 
  explosion 
  or 
  swallowed 
  

   up 
  by 
  an 
  equally 
  great 
  engulfment. 
  

  

  The 
  occurrence 
  of 
  a 
  distinct 
  rim 
  at 
  once 
  looks 
  favorable 
  to 
  

   the 
  explosion 
  method, 
  for 
  rims 
  more 
  or 
  less 
  complete, 
  made 
  

   up 
  of 
  the 
  ejected 
  materials, 
  are 
  known 
  about 
  many 
  pits 
  formed 
  

   in 
  that 
  way.* 
  As 
  we 
  have 
  already 
  seen, 
  however, 
  the 
  rim 
  is 
  

   neither 
  made 
  up 
  wholly 
  or 
  in 
  any 
  part 
  of 
  fragments 
  blown 
  out 
  

   of 
  the 
  pit, 
  but, 
  on 
  the 
  contrary, 
  is 
  composed 
  throughout 
  of 
  

   layers 
  of 
  solid 
  lava, 
  alternating 
  with 
  those 
  of 
  volcanic 
  con- 
  

   glomerate 
  and 
  tuff, 
  all 
  of 
  which 
  were 
  erupted 
  from 
  Mt. 
  

   Mazama 
  before 
  the 
  pit 
  originated. 
  There 
  are, 
  indeed, 
  great 
  

   quantities 
  of 
  pumice 
  in 
  the 
  region, 
  but 
  that 
  is, 
  at 
  least 
  in 
  part, 
  

   clearly 
  associated 
  with 
  the 
  last 
  eruptions 
  of 
  Mt. 
  Mazama, 
  for 
  

   it 
  underlies 
  some 
  of 
  the 
  latest 
  flows, 
  and 
  differs 
  widely 
  from 
  

   the 
  material 
  (andesite) 
  of 
  which 
  the 
  basal 
  portion 
  of 
  that 
  great 
  

   volcano 
  was 
  made 
  up. 
  The 
  entire 
  lack, 
  about 
  the 
  pit, 
  of 
  

   material 
  corresponding 
  in 
  kind, 
  form 
  or 
  quantity 
  to 
  that 
  which 
  

   would 
  necessarily 
  arise, 
  if 
  the 
  pit 
  were 
  produced 
  by 
  a 
  great 
  

   explosion, 
  compels 
  us 
  to 
  look 
  in 
  the 
  other 
  direction 
  for 
  the 
  

   solution 
  of 
  the 
  problem. 
  

  

  While 
  it 
  is 
  true, 
  as 
  shown 
  by 
  Lyell,f 
  Scrope,;): 
  Judd,§ 
  

   Geikie|| 
  and 
  others 
  that 
  the 
  majority 
  of 
  crater 
  lakes 
  occupy 
  

   basins 
  produced 
  by 
  volcanic 
  explosions 
  alone, 
  there 
  are 
  others, 
  

   which 
  the 
  same 
  authors 
  recognize 
  as 
  occupying 
  areas 
  a 
  portion 
  

   of 
  whose 
  depression 
  is 
  attributed 
  to 
  subsidence. 
  Lake 
  Lonar 
  

   in 
  India 
  has 
  a 
  low 
  rim 
  of 
  fragmental 
  material, 
  but 
  its 
  volume 
  

   is 
  much 
  less 
  than 
  that 
  of 
  the 
  pit 
  which 
  it 
  surrounds. 
  For 
  this 
  

   reason 
  the 
  pit 
  is 
  ascribed 
  chiefly 
  to 
  subsidence. 
  Major 
  DuttonT 
  

   has 
  pointed 
  out 
  a 
  number 
  of 
  similar 
  sunken 
  areas 
  or 
  pits, 
  but 
  

   without 
  lakes, 
  in 
  the 
  Hawaiian 
  Islands, 
  and 
  Dana 
  has 
  described** 
  

   the 
  sinking 
  of 
  the 
  lava 
  column 
  (molten 
  material), 
  thus 
  deepen- 
  

   ing 
  the 
  pit, 
  in 
  the 
  yet 
  active 
  volcano 
  of 
  Kilauea. 
  The 
  subsi- 
  

   dence 
  of 
  the 
  molten 
  material 
  in 
  the 
  throat 
  of 
  the 
  volcano 
  and 
  

  

  * 
  Yolcanoes: 
  The 
  character 
  of 
  their 
  phenomena, 
  etc., 
  by 
  G. 
  Poulett. 
  Scrope 
  r 
  

   p. 
  215. 
  

  

  f 
  Elements 
  of 
  Geology, 
  sixth 
  edition, 
  pp. 
  679-82. 
  

  

  \ 
  Volcanoes, 
  The 
  character 
  of 
  their 
  phenomena, 
  etc. 
  G. 
  Poulett, 
  Scrope, 
  pp. 
  

   222-225. 
  

  

  § 
  Volcanoes, 
  by 
  J. 
  W. 
  Judd, 
  pp. 
  170-171. 
  

  

  || 
  Text-Book 
  of 
  Geology, 
  third 
  edition, 
  p. 
  240. 
  

  

  ^[ 
  Major 
  Dutton 
  who 
  made 
  a 
  study 
  of 
  Crater 
  Lake, 
  after 
  having 
  visited 
  the 
  

   great 
  volcanoes 
  of 
  the 
  Hawaiian 
  Islands, 
  came 
  to 
  the 
  conclusion 
  that 
  this 
  depres- 
  

   sion 
  was 
  'formed 
  in 
  the 
  same 
  manner 
  as 
  the 
  great 
  calderas 
  of 
  the 
  Hawaii 
  

   Islands" 
  (U. 
  S. 
  Geol. 
  Survey, 
  Eighth 
  Annual 
  Report, 
  p. 
  158), 
  that 
  is, 
  " 
  by 
  the 
  

   dropping 
  of 
  a 
  block 
  of 
  the 
  mountain 
  crust 
  which 
  once 
  covered 
  a 
  reservoir 
  of 
  

   lava, 
  this 
  reservoir 
  being 
  tapped 
  and 
  drained 
  by 
  eruptions 
  at 
  much 
  lower 
  levels." 
  

   (U. 
  S. 
  Geol. 
  Survey, 
  Fourth 
  Annual 
  Report, 
  p. 
  105.) 
  

  

  ** 
  Characteristics 
  of 
  Volcanoes 
  (1891) 
  p. 
  127, 
  and 
  Manual 
  of 
  Geology, 
  fourth, 
  

   edition, 
  pp. 
  284-5. 
  

  

  