﻿24 
  0. 
  Holtedahl 
  — 
  Paleo 
  geography 
  and 
  

  

  here 
  also 
  recall 
  Daly's 
  theory 
  of 
  intrusions 
  in 
  the 
  deeper 
  

   part 
  of 
  the 
  crust 
  as 
  a 
  cause 
  of 
  deformations 
  in 
  the 
  upper- 
  

   most 
  part, 
  the 
  only 
  one 
  that 
  we 
  can 
  study. 
  

  

  Taking 
  the 
  deformation 
  zone 
  of 
  Norway, 
  for 
  example, 
  

   where, 
  as 
  has 
  been 
  emphasized, 
  a 
  fairly 
  deeply 
  situated 
  

   part 
  of 
  the 
  crust 
  may 
  be 
  studied, 
  the 
  amount 
  of 
  intruded 
  

   material 
  is 
  so 
  enormous 
  that 
  it 
  does 
  not 
  at 
  all 
  s'eem 
  un- 
  

   reasonable 
  to 
  consider 
  these 
  masses 
  as 
  having 
  played 
  a 
  

   more 
  important 
  role 
  than 
  that 
  of 
  a 
  passive 
  element 
  only, 
  

   for 
  which 
  the 
  way 
  was 
  opened 
  from 
  the 
  abyss 
  to 
  higher 
  

   zones 
  by 
  the 
  deformation. 
  That 
  intruded 
  masses 
  are 
  not 
  

   known 
  from 
  all 
  folded 
  ranges 
  may 
  not 
  necessarily 
  mean 
  

   that 
  they 
  do 
  not 
  occur 
  at 
  greater 
  and 
  inaccessible 
  depths. 
  

  

  Yet 
  if 
  we 
  consider 
  how, 
  as 
  becomes 
  more 
  and 
  more 
  

   evident, 
  orogenic 
  movements, 
  speaking 
  generally, 
  occur 
  

   again 
  and 
  again 
  in 
  the 
  same 
  main 
  belts 
  of 
  the 
  earth, 
  it 
  

   is 
  difficult 
  to 
  understand 
  how 
  this 
  may 
  be 
  explained 
  by 
  

   the 
  theory 
  of 
  magmatic 
  flow 
  only. 
  

  

  Even 
  if 
  we 
  do 
  not 
  at 
  present 
  understand 
  why 
  these 
  

   belts 
  are 
  the 
  ones 
  especially 
  subjected 
  to 
  folding, 
  or 
  why 
  

   the 
  geosynclines 
  come 
  into 
  existence 
  just 
  here, 
  the 
  re- 
  

   peated 
  movement 
  in 
  these 
  zones, 
  with 
  periods 
  of 
  quiet 
  

   between, 
  seems 
  without 
  doubt 
  to 
  harmonize 
  with 
  the 
  old 
  

   theory 
  of 
  contraction. 
  If 
  we 
  apply 
  the 
  theory 
  of 
  under- 
  

   flow, 
  we 
  must 
  have 
  a 
  more 
  primary 
  condition 
  explaining 
  

   the 
  remarkable 
  location 
  of 
  the 
  orogenic 
  movements. 
  

   Certainly 
  the 
  occurrence 
  of 
  the 
  orogenic 
  zones 
  along 
  the 
  

   ocean 
  borders 
  is 
  a 
  fact 
  of 
  fundamental 
  importance, 
  as 
  

   has 
  been 
  pointed 
  out 
  by 
  Andree 
  (Ueber 
  die 
  Bedingungen 
  

   der 
  Gebirgsbildung, 
  Berlin, 
  1914, 
  pp. 
  60-61), 
  and 
  A. 
  

   Wegener 
  3 
  supposes 
  the 
  shelves 
  to 
  be 
  belts 
  of 
  weakness 
  

   because 
  the 
  salic 
  zone 
  here 
  is 
  thought 
  to 
  be 
  relatively 
  

   thin, 
  and 
  further, 
  because 
  the 
  difference 
  in 
  density 
  

   between 
  adjacent 
  areas, 
  oceanic 
  (simic) 
  and 
  continental 
  

   (salic), 
  is 
  rather 
  important. 
  Yet 
  as 
  has 
  been 
  previously 
  

   emphasized, 
  the 
  northwest 
  European 
  geosyncline 
  was 
  

  

  3 
  1 
  shall 
  not 
  enter 
  here 
  into 
  any 
  discussion 
  of 
  the 
  very 
  daring 
  — 
  in 
  my 
  

   opinion 
  far 
  too 
  daring 
  — 
  hypothesis 
  of 
  Wegener 
  (Die 
  Entstehung 
  der 
  Kon- 
  

   tinente 
  und 
  Ozeane, 
  Braunschweig, 
  1915), 
  according 
  to 
  which 
  the 
  separa- 
  

   tion 
  of 
  America 
  and 
  Europe 
  was 
  caused 
  by 
  a 
  horizontal 
  movement 
  of 
  the 
  

   upper 
  or 
  salic 
  zone 
  of 
  the 
  crust, 
  a 
  movement 
  that, 
  so 
  far 
  as 
  the 
  northern 
  

   part 
  of 
  the 
  Atlantic 
  area 
  is 
  concerned, 
  is 
  supposed 
  to 
  have 
  taken 
  place 
  in 
  

   Quaternary 
  time. 
  Far 
  from 
  being 
  more 
  easily 
  explained 
  in 
  the 
  light 
  

   of 
  this 
  hypothesis 
  (which 
  postulates 
  the 
  existence 
  of 
  a 
  coherent 
  continental 
  

   mass 
  embracing 
  both 
  the 
  new 
  and 
  the 
  old 
  world, 
  with 
  no 
  Atlantic 
  ' 
  l 
  fissure, 
  ' 
  ' 
  

   in 
  pre-Cenozoic 
  time!), 
  several 
  of 
  the 
  facts 
  mentioned 
  in 
  the 
  preceding 
  

   pages 
  do 
  not 
  at 
  all 
  harmonize 
  with 
  it. 
  

  

  