﻿12 
  G. 
  II. 
  Stone 
  — 
  Glaciation 
  of 
  Central 
  Idaho. 
  

  

  matter 
  whether 
  the 
  glacial 
  river 
  flowed 
  in 
  a 
  sub 
  glacial, 
  or 
  

   englacial, 
  or 
  in 
  a 
  superficial 
  channel 
  during 
  the 
  time 
  of 
  rapid 
  

   flow 
  of 
  the 
  ice, 
  it 
  must 
  have 
  flowed 
  in 
  an 
  open 
  ice 
  canon 
  dur- 
  

   ing 
  the 
  period 
  of 
  stagnation. 
  Into 
  this 
  canon 
  trees 
  that 
  were 
  

   growing 
  on 
  the 
  glacier 
  fell 
  as 
  they 
  were 
  undermined 
  by 
  the 
  

   melting 
  of 
  the 
  ice 
  walls 
  of 
  the 
  channel. 
  The 
  fact 
  that 
  the 
  

   trunks 
  were 
  broken 
  into 
  so 
  small 
  fragments 
  indicates 
  more 
  

   force 
  than 
  is 
  usual 
  in 
  the 
  case 
  of 
  ordinary 
  stream 
  channels. 
  

   Probably 
  the 
  motion 
  of 
  the 
  ice 
  helped 
  to 
  break 
  up 
  the 
  trees, 
  

   assisted 
  by 
  ice 
  and 
  timber 
  dams 
  or 
  gorges. 
  

  

  The 
  occurrence 
  of 
  wood 
  in 
  the 
  esker 
  gravels 
  of 
  Idaho 
  sug- 
  

   gests 
  a 
  comparison 
  of 
  that 
  region 
  with 
  New 
  England. 
  

  

  In 
  New 
  England 
  there 
  were 
  many 
  level 
  regions, 
  especially 
  

   in 
  Maine 
  to 
  the 
  north 
  of 
  east-and-west 
  ranges 
  of 
  hills, 
  where 
  

   the 
  ice 
  would 
  naturally 
  become 
  stagnant 
  during 
  the 
  final 
  melt- 
  

   ing 
  and 
  retreat 
  of 
  the 
  great 
  ice 
  sheet. 
  The 
  Idaho 
  facts 
  suggest 
  

   that 
  if 
  vegetation 
  crowded 
  close 
  on 
  the 
  front 
  of 
  the 
  New 
  Eng- 
  

   land 
  ice 
  sheet, 
  the 
  stagnant 
  ice 
  ought 
  there 
  to 
  become 
  forested 
  

   as 
  in 
  Idaho. 
  In 
  this 
  case 
  we 
  ought 
  to 
  And 
  pieces 
  of 
  wood 
  in 
  

   the 
  broad 
  osar 
  plains 
  of 
  Maine 
  and 
  in 
  such 
  portions 
  of 
  the 
  

   valley 
  drift 
  as 
  were 
  glacial 
  overwash. 
  No 
  wood 
  or 
  other 
  land 
  

   organic 
  remains 
  have 
  yet 
  been 
  found 
  in 
  these 
  deposits 
  in 
  

   Maine, 
  though 
  Emerson 
  has 
  found 
  in 
  the 
  Connecticut 
  valley 
  

   vegetable 
  remains 
  in 
  sediments 
  of 
  glacial 
  age. 
  The 
  absence 
  of 
  

   wood 
  from 
  the 
  eskers 
  and 
  valley 
  drift 
  of 
  all 
  of 
  northern 
  and 
  

   northeastern 
  New 
  England 
  can 
  fairly 
  be 
  urged 
  as 
  proving 
  that 
  

   forests 
  did 
  not 
  press 
  closely 
  on 
  the 
  front 
  of 
  the 
  retreating 
  ice 
  

   sheet 
  in 
  that 
  region. 
  This 
  is 
  supported 
  by 
  another 
  considera- 
  

   tion, 
  viz., 
  that 
  at 
  the 
  time 
  of 
  maximum 
  glaciation 
  the 
  ice 
  con- 
  

   fronted 
  the 
  sea 
  along 
  the 
  whole 
  New 
  England 
  coast. 
  When 
  

   the 
  ice 
  retreated, 
  vegetation 
  would 
  have 
  to 
  advance 
  a 
  long 
  way 
  

   eastward 
  as 
  well 
  as 
  northward 
  in 
  order 
  to 
  reach 
  Maine 
  from 
  

   New 
  Jersey, 
  the 
  nearest 
  land 
  then 
  covered 
  by 
  vegetation, 
  

   unless 
  possibly 
  we 
  except 
  Nova 
  Scotia. 
  The 
  above 
  considera- 
  

   tions 
  make 
  it 
  probable 
  that 
  the 
  stagnant 
  marginal 
  portions 
  of 
  

   the 
  retreating 
  New 
  England 
  ice 
  sheet 
  did 
  not 
  become 
  forested, 
  

   at 
  least 
  toward 
  the 
  northeast. 
  

  

  The 
  large 
  valley 
  ice 
  sheets 
  or 
  Piedmont 
  glaciers 
  of 
  north- 
  

   central 
  Idaho 
  formed 
  a 
  type 
  intermediate 
  in 
  character 
  between 
  

   the 
  more 
  strictly 
  local 
  glaciers 
  found 
  farther 
  south, 
  and 
  the 
  

   great 
  confluent 
  ice 
  sheet 
  of 
  British 
  Columbia. 
  

  

  November, 
  1899. 
  

  

  