﻿ACADEMY 
  OP 
  SCIENCES. 
  421 
  

  

  plants 
  found 
  fossile 
  in 
  onr 
  coal 
  measures 
  are 
  of 
  a 
  more 
  temperate 
  group 
  than 
  

   those 
  of 
  the 
  cretaceous 
  coal 
  beds 
  of 
  Vancouver 
  Island, 
  which, 
  if 
  so, 
  will 
  be 
  

   good 
  evidence 
  of 
  their 
  indicating 
  a 
  newer 
  age. 
  

  

  Have 
  the 
  poles 
  changed? 
  1, 
  It 
  will 
  appear, 
  from 
  the 
  preceding 
  remarks, 
  

   that 
  it 
  is 
  not 
  necessary 
  to 
  suppose 
  a 
  change 
  of 
  the 
  poles 
  to 
  account 
  for 
  the 
  ab- 
  

   sence 
  of 
  eocene 
  fossils 
  in 
  California 
  ; 
  but 
  I 
  still 
  believe 
  that 
  the 
  existence 
  of 
  

   tropical 
  and 
  temperate 
  groups 
  of 
  beings 
  within 
  the 
  Arctic 
  circle, 
  from 
  the 
  mio- 
  

   cene 
  back 
  to 
  the 
  carboniferous 
  age, 
  proves 
  either 
  such 
  a 
  change, 
  or 
  the 
  existence 
  

   of 
  some 
  light-giving 
  medium 
  there 
  in 
  those 
  ages, 
  of 
  which 
  we 
  have 
  no 
  knowl- 
  

   edge. 
  It 
  is 
  easy 
  to 
  account 
  for 
  a 
  hot 
  climate 
  there, 
  either 
  by 
  supposing 
  the 
  in- 
  

   ternal 
  heat 
  of 
  the 
  globe 
  to 
  have 
  been 
  greater, 
  and 
  the 
  amount 
  of 
  radiation 
  less, 
  

   or 
  by 
  the 
  existence 
  of 
  hotter 
  regions 
  of 
  space 
  through 
  which 
  the 
  solar 
  system 
  

   was 
  then 
  traveling, 
  but 
  that 
  alone 
  could 
  not 
  produce 
  the 
  vegetation 
  found 
  there. 
  

  

  2. 
  An 
  increase 
  in 
  the 
  obliquity 
  of 
  the 
  earth's 
  position 
  in 
  its 
  orbit 
  could 
  only 
  

   present 
  each 
  pole 
  alternately 
  to 
  the 
  sun, 
  though 
  more 
  directly 
  than 
  now, 
  so 
  that, 
  

   while 
  each 
  hemisphere 
  would 
  have 
  six 
  mnnths 
  of 
  greater 
  heat 
  and 
  constant 
  light, 
  

   they 
  would 
  also 
  have 
  six 
  months 
  of 
  greater 
  cold 
  and 
  darkness. 
  

  

  3. 
  Juding 
  from 
  what 
  we 
  know, 
  a 
  vegetation 
  so 
  much 
  like 
  ours 
  could 
  not 
  

   exist 
  in 
  a 
  climate 
  very 
  diff't-rent 
  from 
  ours, 
  for 
  we 
  find 
  entirely 
  different 
  vegetation 
  

   in 
  regions 
  both 
  north 
  and 
  south 
  of 
  us, 
  having 
  comparatively 
  similar 
  climates. 
  

   A 
  duration 
  of 
  day 
  or 
  night, 
  for 
  months, 
  would 
  be 
  as 
  great 
  a 
  change 
  as 
  one 
  of 
  

   many 
  degrees 
  of 
  temperature. 
  A 
  four-months 
  night, 
  with 
  warm 
  climate, 
  would 
  

   either 
  blanch 
  or 
  decay 
  nearly 
  all 
  growth 
  above 
  ground. 
  

  

  4. 
  The 
  objection 
  that 
  the 
  flattening 
  of 
  the 
  poles 
  proves 
  a 
  permanent 
  posi- 
  

   tion 
  of 
  the 
  earth's 
  axis, 
  although 
  now 
  true, 
  if 
  the 
  earth 
  is 
  nearly 
  solid, 
  need 
  not 
  

   have 
  been 
  so 
  when 
  it 
  was 
  semi-fluid 
  in 
  the 
  interior, 
  with 
  a 
  thinner 
  crust. 
  Even 
  

   now, 
  if 
  the 
  earth 
  was 
  to 
  stop 
  revolving, 
  the 
  water 
  must 
  run 
  from 
  the 
  equator 
  

   towards 
  the 
  poles, 
  and 
  cover 
  them 
  deeply 
  enough 
  to 
  restore 
  nearly 
  the 
  perfect 
  

   spherical 
  form, 
  at 
  the 
  same 
  time 
  uncovering 
  much 
  of 
  the 
  land 
  now 
  submerged 
  

   in 
  the 
  tropics. 
  The 
  flattest 
  parts 
  of 
  the 
  sphere 
  would 
  then 
  be 
  the 
  deep 
  bed 
  of 
  

   the 
  ocean 
  in 
  or 
  near 
  the 
  tropics. 
  The 
  difference 
  between 
  them 
  and 
  the 
  summit 
  

   of 
  the 
  Andes 
  or 
  Himalayas, 
  is 
  nearly 
  as 
  great 
  as 
  that 
  between 
  the 
  convexities 
  

   at 
  the 
  poles 
  and 
  the 
  equator. 
  

  

  5. 
  The 
  objection 
  that 
  no 
  cause 
  is 
  known 
  that 
  could 
  produce 
  a 
  change 
  in 
  the 
  

   earth's 
  axis, 
  is 
  answered 
  by 
  the 
  geological 
  evidence 
  of 
  periodical 
  changes 
  in 
  the 
  

   elevation 
  of 
  the 
  land, 
  amounting 
  to 
  many 
  thousand 
  feet, 
  which 
  must, 
  it 
  seems, 
  

   cause 
  a 
  change 
  in 
  the 
  center 
  of 
  gravity 
  of 
  the 
  earth, 
  and 
  a 
  consequent 
  shifting 
  

   of 
  its 
  axis, 
  not 
  to 
  mention 
  the 
  disturbing 
  effect 
  of 
  the 
  attraction 
  of 
  aste- 
  

   roids, 
  etc. 
  

  

  6. 
  Astronomical 
  observations, 
  extending 
  back 
  only 
  about 
  4,000 
  years, 
  may 
  

   prove 
  that 
  no 
  perceptible 
  change 
  has 
  occurred 
  since 
  then, 
  but 
  cannot 
  concern 
  

   preceding 
  ages. 
  The 
  earth's 
  present 
  oblique 
  position 
  is 
  itself 
  good 
  evidence 
  

   that 
  the 
  distribution 
  of 
  land 
  and 
  water 
  has 
  disturbed 
  its 
  axis 
  from 
  a 
  position 
  in 
  

   which 
  the 
  equator 
  would 
  be 
  always 
  turned 
  directly 
  toward 
  the 
  sun, 
  as 
  in 
  our 
  

   semi-annual 
  equinoxes. 
  

  

  