﻿222 
  DR. 
  J. 
  CROLL 
  ON 
  PREVAILING 
  MISCONCEPTIONS 
  REGARDING 
  

  

  absence 
  may 
  be 
  the 
  indication 
  either 
  of 
  a 
  period 
  of 
  extreme 
  glacia- 
  

   tion 
  or 
  of 
  a 
  period 
  absolutely 
  free 
  from 
  ice. 
  This 
  absence 
  is 
  a 
  result 
  

   which 
  would 
  as 
  truly 
  follow 
  from 
  the 
  former 
  condition 
  of 
  things 
  as 
  

   from 
  the 
  latter. 
  Glaciers 
  carry 
  erratic 
  blocks 
  on 
  their 
  surfaces, 
  

   but 
  such 
  blocks 
  are 
  seldom, 
  if 
  ever, 
  on 
  the 
  surface 
  of 
  an 
  ice-sheet. 
  

   The 
  reason 
  is 
  obvious. 
  When 
  a 
  country 
  is 
  completely 
  buried 
  under 
  

   ice 
  there 
  is 
  no 
  source 
  from 
  which 
  the 
  ice 
  can 
  obtain 
  erratics 
  on 
  its 
  

   surface. 
  The 
  stones 
  which 
  lie 
  under 
  the 
  ice, 
  before 
  they 
  can 
  reach 
  

   the 
  sea, 
  are 
  ground 
  down 
  to 
  powder. 
  Large 
  erratic 
  blocks 
  have 
  

   never 
  been 
  found, 
  for 
  example, 
  on 
  the 
  ice-sheet 
  of 
  Greenland. 
  iSTo 
  

   one, 
  of 
  course, 
  has 
  as 
  yet 
  had 
  an 
  opportunity 
  of 
  examining 
  the 
  surface 
  

   of 
  the 
  Antarctic 
  ice 
  ; 
  but 
  judging 
  from 
  the 
  character 
  of 
  the 
  icebergs 
  

   derived 
  from 
  it, 
  we 
  are 
  almost 
  certain 
  that 
  it 
  contains 
  no 
  boulders. 
  

   Were 
  the 
  seas 
  surrounding 
  these 
  continents 
  elevated 
  into 
  dry 
  land, 
  

   a 
  geologist, 
  judging 
  from 
  the 
  comparative 
  absence 
  of 
  boulders 
  in 
  the 
  

   sedimentary 
  deposits 
  which 
  have 
  been 
  forming 
  for 
  the 
  past 
  thousands 
  

   of 
  years, 
  would 
  be 
  apt 
  to 
  conclude 
  that 
  these 
  continents 
  had 
  

   never 
  been 
  covered 
  by 
  ice. 
  In 
  fact, 
  a 
  conclusion 
  of 
  this 
  kind 
  has 
  

   been 
  arrived 
  at 
  by 
  Prof. 
  ]S 
  T 
  ordenskjold, 
  who 
  maintains, 
  because 
  he 
  has 
  

   never 
  seen 
  in 
  the 
  strata 
  of 
  Greenland 
  or 
  Spitzbergen 
  a 
  boulder 
  larger 
  

   than 
  a 
  child's 
  head, 
  that 
  down 
  to 
  the 
  termination 
  of 
  the 
  Uiocene 
  

   period 
  no 
  glacial 
  condition 
  of 
  things 
  existed 
  in 
  these 
  regions— 
  a 
  

   conclusion 
  most 
  certainly 
  utterly 
  erroneous. 
  jNow 
  both 
  of 
  these 
  

   lands 
  are 
  at 
  present 
  in 
  a 
  state 
  of 
  glaciation 
  ; 
  and 
  were 
  it 
  not 
  for 
  the 
  

   enormous 
  quantity 
  of 
  heat 
  which 
  is 
  constantly 
  carried 
  northwards 
  

   from 
  the 
  equatorial 
  regions 
  by 
  the 
  Gulf-stream, 
  not 
  only 
  Greenland 
  

   and 
  Spitzbergen, 
  but 
  the 
  whole 
  of 
  the 
  Arctic 
  regions 
  would 
  be 
  far 
  

   more 
  completely 
  under 
  ice 
  than 
  they 
  are. 
  A 
  glacial 
  state 
  of 
  things 
  

   is 
  the 
  normal 
  condition 
  of 
  Polar 
  regions 
  ; 
  and 
  if 
  at 
  any 
  time, 
  as 
  

   during 
  the 
  Tertiary 
  age, 
  the 
  Arctic 
  regions 
  were 
  free 
  from 
  snow 
  

   and 
  ice, 
  it 
  could 
  only 
  be 
  in 
  consequence 
  of 
  some 
  peculiar 
  distribution 
  

   of 
  land 
  and 
  water 
  and 
  other 
  exceptional 
  conditions. 
  That 
  this 
  

   peculiar 
  combination 
  of 
  circumstances 
  should 
  have 
  existed 
  during 
  

   the 
  whole 
  of 
  that 
  immense 
  lapse 
  of 
  time 
  between 
  the 
  Silurian 
  and 
  

   the 
  close 
  of 
  the 
  Tertiary 
  period 
  is 
  certainly 
  improbable 
  in 
  the 
  highest 
  

   degree 
  : 
  in 
  short, 
  that 
  Greenland 
  during 
  the 
  whole 
  of 
  that 
  time 
  

   should 
  have 
  been 
  free 
  from 
  snow 
  and 
  ice 
  is 
  as 
  improbable, 
  although 
  

   perhaps 
  not 
  so 
  physically 
  impossible, 
  as 
  that 
  the 
  interior 
  of 
  that 
  

   continent 
  should 
  at 
  the 
  present 
  day 
  be 
  free 
  from 
  ice 
  and 
  covered 
  

   with 
  luxuriant 
  vegetation. 
  

  

  In 
  fact, 
  it 
  is 
  the 
  severity 
  of 
  glacial 
  conditions 
  in 
  these 
  regions 
  

   during 
  glacial 
  periods 
  that 
  has 
  rendered 
  the 
  strata 
  to 
  which 
  Prof. 
  

   Nordenskjold 
  refers 
  so 
  comparatively 
  free 
  from 
  erratic 
  blocks. 
  Had 
  

   these 
  regions 
  been 
  occupied 
  by 
  glaciers 
  reaching 
  to 
  the 
  sea, 
  instead 
  

   of 
  being 
  covered 
  by 
  a 
  sheet 
  of 
  ice, 
  boulders 
  in 
  the 
  strata 
  would 
  no 
  

   doubt 
  have 
  been 
  far 
  more 
  common. 
  

  

  As 
  evidence 
  of 
  former 
  glacial 
  periods 
  we 
  may, 
  however, 
  expect 
  to 
  

   find 
  in 
  temperate 
  regions 
  erracic 
  blocks, 
  imbedded 
  here 
  and 
  there 
  in 
  

   the 
  stratified 
  rocks, 
  which 
  may 
  have 
  been 
  transported 
  by 
  icebergs 
  

   and 
  dropped 
  into 
  the 
  sea. 
  But 
  unless 
  the 
  glaciers 
  of 
  such 
  epochs 
  

  

  