﻿224 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  glacial 
  erosion. 
  It 
  requires 
  from 
  the 
  glacier, 
  that 
  at 
  best 
  could 
  have 
  

   had 
  but 
  comparatively 
  short 
  headings, 
  and 
  must 
  soon 
  have 
  spread 
  over 
  

   a 
  very 
  wide 
  area, 
  thus 
  losing 
  in 
  active 
  force, 
  more 
  work 
  than 
  in 
  my 
  esti- 
  

   mation 
  a 
  glacier 
  of 
  such 
  original 
  extent 
  could 
  have 
  performed. 
  

  

  As 
  the 
  last 
  question 
  involved 
  in 
  the 
  discussion 
  of 
  the 
  ancient 
  glaciers 
  

   of 
  Southern 
  Colorado, 
  we 
  have 
  to 
  consider 
  their 
  origin. 
  Without 
  enter- 
  

   ing 
  into 
  an 
  elaborate 
  discussion 
  on 
  glacial 
  periods 
  in 
  general, 
  I 
  shall 
  cite 
  

   such 
  instances 
  as 
  may 
  corroborate 
  the 
  views 
  I 
  hold 
  with 
  regard 
  to 
  the 
  

   subject.* 
  From 
  many 
  localities 
  west 
  of 
  the 
  Missouri 
  Eiver, 
  evidences 
  of 
  

   ancient 
  glaciers 
  have 
  been 
  mentioned 
  by 
  geologists 
  exploring 
  the 
  count 
  

   try. 
  Professor 
  Newberry 
  enumerates 
  a 
  large 
  number 
  from 
  the 
  Cascade 
  

   Eange,t 
  including 
  in 
  the 
  glaciated 
  area 
  Mounts 
  Hood, 
  Rainier, 
  Adams, 
  

   and 
  others. 
  Wbitney| 
  cites 
  many 
  localities 
  in 
  that 
  State 
  where 
  the 
  

   traces 
  of 
  former 
  glaciers 
  have 
  been 
  found. 
  In 
  Arizona, 
  New 
  Mexico, 
  

   Utah, 
  Colorado, 
  and 
  other 
  Territories, 
  they 
  have 
  been 
  observed, 
  and 
  are 
  

   described 
  in 
  the 
  reports 
  of 
  the 
  various 
  surveying 
  and 
  exploring 
  expe- 
  

   ditions. 
  We 
  have, 
  therefore, 
  numerous 
  ancient 
  glaciers 
  spread 
  over 
  an 
  

   enormous 
  area 
  of 
  country. 
  For 
  those 
  of 
  the 
  Cascade 
  Range 
  Newberry 
  

   claims 
  the 
  same 
  period 
  of 
  time 
  that 
  is 
  assigned 
  to 
  the 
  great 
  glacial 
  epoch 
  

   of 
  our 
  central 
  continental 
  regions. 
  Gilbert 
  § 
  describes 
  a 
  number 
  of 
  the 
  

   phenomena 
  he 
  has 
  observed, 
  and 
  explains 
  some 
  of 
  the 
  orographic 
  feat- 
  

   ures 
  of 
  the 
  regions 
  he 
  examined 
  as 
  owing 
  their 
  present 
  characteristics 
  

   to 
  the 
  iutluence 
  of 
  moving 
  ice. 
  Gilbert 
  comes 
  to 
  the 
  conclusion 
  || 
  that 
  

   the 
  " 
  general 
  glaciation 
  of 
  the 
  Eastern 
  United 
  States 
  had 
  no 
  counter- 
  

   part 
  in 
  the 
  same 
  latitudes, 
  over 
  the 
  region 
  extending 
  from 
  the 
  Rocky 
  

   Mountains 
  to 
  the 
  Sierra 
  Nevada 
  inclusive", 
  and 
  elaborates 
  this 
  state- 
  

   ment 
  by 
  saying 
  that 
  " 
  the 
  phenomena 
  of 
  the 
  glacial 
  epoch 
  at 
  the 
  west 
  

   differed 
  from 
  the 
  synchronous 
  phenomena 
  in 
  the 
  same 
  latitudes 
  at 
  the 
  

   East, 
  for 
  the 
  reason 
  that 
  then, 
  as 
  now, 
  the 
  former 
  region 
  was 
  compara- 
  

   tively 
  arid, 
  and 
  material 
  was 
  lacking 
  for 
  a 
  great 
  ice-field". 
  It 
  is 
  to 
  be 
  

   understood, 
  then, 
  from 
  these 
  expressions, 
  that 
  the 
  glaciation 
  of 
  our 
  

   western 
  country 
  did 
  not 
  partake 
  of 
  the 
  same 
  character 
  as 
  that 
  farther 
  

   east. 
  In 
  other 
  words, 
  instead 
  of 
  having 
  a 
  great 
  expanse 
  covered 
  by 
  

   ice, 
  we 
  have, 
  owing 
  to 
  the 
  " 
  arid" 
  character 
  of 
  the 
  region, 
  but 
  isolated 
  

   groups 
  of 
  glaciers. 
  It 
  seems 
  to 
  me, 
  in 
  case 
  a 
  general 
  glacial 
  epoch 
  is 
  

   accepted 
  for 
  our 
  entire 
  continent, 
  that 
  the 
  orographic 
  and 
  topographical 
  

   features 
  of 
  the 
  country 
  "from 
  the 
  Rocky 
  Mountains 
  to 
  the 
  Sierra 
  

   Nevada 
  inclusive" 
  might 
  more 
  effectually 
  account 
  for 
  the 
  absence 
  of 
  a 
  

   " 
  great 
  ice-field 
  " 
  than 
  the 
  want 
  of 
  moisture. 
  At 
  the 
  same 
  time 
  it 
  

   becomes 
  a 
  matter 
  of 
  some 
  difficulty 
  to 
  reconcile 
  the 
  "then 
  as 
  now" 
  

   " 
  arid" 
  character 
  of 
  the 
  country 
  to 
  conclusion 
  No. 
  Ill 
  at 
  which 
  Gilbert 
  

   arrives. 
  He 
  says:Tf 
  "There 
  was 
  a 
  general 
  accession 
  of 
  water 
  to 
  the 
  

   valleys 
  of 
  the 
  great 
  basin, 
  [during 
  the 
  period 
  of 
  glaciation, 
  would 
  un- 
  

   doubtedly 
  he 
  understood 
  from 
  the 
  connection 
  this 
  sentence 
  Ms 
  with 
  the 
  pre- 
  

   ceding 
  and 
  following. 
  — 
  E.] 
  Lakes 
  were 
  formed 
  where 
  now 
  are 
  only 
  

   deserts, 
  and 
  valleys, 
  now 
  nearly 
  empty, 
  were 
  filled 
  to 
  overflowing." 
  

  

  Two 
  conditions, 
  above 
  all, 
  are 
  necessary 
  for 
  the 
  formation 
  of 
  glaciers 
  : 
  

   an 
  abundance 
  of 
  precipitated 
  moisture 
  and 
  a 
  low 
  mean 
  annual 
  tem- 
  

  

  * 
  I 
  am 
  at 
  present 
  engaged 
  in 
  preparing 
  a 
  paper 
  on 
  the 
  ancient 
  glaciers 
  of 
  the 
  Rocky 
  

   Mountains 
  and 
  those 
  farther 
  west, 
  in 
  which 
  their 
  correlations 
  with 
  each 
  other 
  and 
  with 
  

   the 
  great 
  ice-period 
  shall 
  be 
  more 
  fully 
  treated 
  of. 
  

  

  t 
  Report 
  on 
  Northern 
  California 
  and' 
  Oregon, 
  18.j7, 
  p. 
  4'^, 
  and 
  Pop. 
  Sci. 
  Monthly, 
  1376, 
  

   p. 
  289. 
  

  

  X 
  Geological 
  Survey 
  of 
  California, 
  Tol.i, 
  1865. 
  

  

  ij 
  Explorations 
  and' 
  Surveys 
  West 
  of 
  the 
  'One 
  Hundredth 
  Meridian, 
  1875, 
  p. 
  86. 
  

  

  II 
  Ibid., 
  p. 
  103. 
  

  

  If 
  Ibid., 
  p. 
  104. 
  

  

  