﻿280 
  ANNUAL 
  REPOET 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  regularity 
  which 
  CroU 
  postulated, 
  the 
  Northern 
  and 
  Southern 
  Hemi- 
  

   spheres 
  must 
  each 
  have 
  had 
  some 
  40,000 
  of 
  them, 
  which 
  does 
  not 
  

   seem 
  likely. 
  

  

  A. 
  (2) 
  Shifting 
  of 
  the 
  earth's 
  axis 
  and 
  the 
  concomitant 
  changes 
  

   in 
  the 
  position 
  of 
  the 
  poles 
  are 
  by 
  most 
  astronomers 
  declared 
  to 
  be 
  

   impossible. 
  Into 
  this 
  astronomical 
  problem 
  we 
  need 
  not 
  enter, 
  for 
  

   no 
  position 
  of 
  the 
  poles 
  which 
  has 
  yet 
  been 
  suggested 
  would 
  get 
  rid 
  

   of 
  the 
  necessity 
  of 
  admitting 
  climatic 
  change. 
  This 
  hypothesis 
  and 
  

   the 
  following 
  one 
  are 
  not, 
  strictly 
  speaking, 
  attempts 
  to 
  explain 
  cli- 
  

   matic 
  changes, 
  but 
  to 
  account 
  for 
  the 
  distribution 
  of 
  fossil 
  floras 
  and 
  

   faunas 
  without 
  assuming 
  important 
  changes 
  in 
  the 
  earth's 
  atmospheric 
  

   temperatures. 
  

  

  A. 
  (3) 
  A 
  shifting 
  of 
  the 
  earth's 
  outer 
  shell 
  on 
  the 
  interior 
  is 
  a 
  

   hypothesis 
  much 
  like 
  the 
  preceding, 
  but 
  differs 
  in 
  the 
  suggested 
  

   mechanism 
  of 
  change. 
  Thus 
  Wegener 
  suggests 
  that 
  the 
  vast 
  Permian 
  

   glaciation 
  in 
  the 
  Southern 
  Hemisphere 
  was 
  due 
  to 
  the 
  junction 
  of 
  

   the 
  southern 
  continents 
  around 
  a 
  pole 
  in 
  the 
  Indian 
  Ocean 
  and 
  that 
  

   they 
  have 
  since 
  drifted 
  apart. 
  But 
  this 
  suggestion, 
  even 
  if 
  true, 
  

   would 
  not 
  account 
  for 
  the 
  facts; 
  as 
  Lake 
  has 
  pointed 
  out, 
  Permian 
  

   ice 
  sheets 
  covered 
  northern 
  Baluchistan, 
  which, 
  according 
  to 
  the 
  

   hypothesis, 
  would 
  then 
  have 
  been 
  in 
  the 
  Tropics. 
  Concerning 
  the 
  

   possibility 
  of 
  the 
  shift 
  itself 
  Jeffreys 
  remarks 
  : 
  

  

  A 
  displacement 
  of 
  this 
  type 
  would 
  produce 
  important 
  climatic 
  changes, 
  but 
  

   so 
  far 
  no 
  agency 
  capable 
  of 
  producing 
  it 
  has 
  been 
  suggested. 
  

  

  A. 
  (4) 
  It 
  was 
  long 
  supposed 
  that 
  the 
  ancient 
  geniality 
  and 
  uni- 
  

   formity 
  which, 
  for 
  such 
  vast 
  stretches 
  of 
  time, 
  characterized 
  the 
  

   earth's 
  climate 
  were 
  due 
  to 
  the 
  internal 
  heat 
  of 
  the 
  globe, 
  and 
  the 
  

   present 
  severe 
  climates 
  of 
  high 
  latitudes 
  have 
  been 
  brought 
  about 
  

   by 
  the 
  reduction 
  of 
  the 
  internal 
  heat 
  by 
  radiation. 
  Aside 
  from 
  the 
  

   question 
  raised 
  by 
  the 
  phenomena 
  of 
  radioactivity, 
  whether 
  the 
  

   earth 
  has 
  actually 
  lost 
  heat 
  (Joly 
  even 
  suggests 
  that 
  it 
  may 
  be 
  gain- 
  

   ing, 
  rather 
  than 
  losing), 
  this 
  hypothesis 
  postulates 
  a 
  continual 
  

   change 
  in 
  one 
  direction 
  and 
  fails 
  to 
  account 
  for 
  fluctuations 
  of 
  cli- 
  

   matic 
  conditions. 
  Since 
  the 
  formation 
  of 
  a 
  solid 
  crust 
  (assuming 
  that 
  

   the 
  globe 
  was 
  once 
  fluid) 
  the 
  very 
  low 
  conductivity 
  of 
  the 
  rocks 
  must 
  

   have 
  prevented 
  the 
  internal 
  heat's 
  having 
  much 
  effect 
  at 
  the 
  surface. 
  

  

  The 
  surface 
  temperature 
  of 
  the 
  earth 
  must 
  have 
  been 
  almost 
  wholly 
  main- 
  

   tained 
  by 
  solar 
  radiation 
  practically 
  ever 
  since 
  it 
  became 
  solid 
  at 
  the 
  surface, 
  

   and 
  certainly 
  throughout 
  geological 
  time. 
  Conduction 
  from 
  the 
  interior 
  is 
  in 
  

   comparison 
  quite 
  unimportant. 
  (Jeffreys.) 
  

  

  B. 
  (1) 
  The 
  foregoing 
  hypotheses 
  all 
  deal 
  with 
  the 
  solid 
  earth 
  as 
  

   a 
  planetary 
  unit, 
  using 
  the 
  term 
  " 
  solid 
  " 
  without 
  prejudice 
  to 
  the 
  

   conception 
  of 
  possible 
  fluid 
  portions 
  of 
  the 
  interior. 
  We 
  may 
  next 
  

   consider 
  the 
  explanations 
  which 
  find 
  the 
  causes 
  of 
  climatic 
  change 
  in 
  

  

  