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  ANNUAL 
  EEPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  recent 
  books 
  appeal 
  to 
  them 
  as 
  all 
  sufficient 
  for 
  the 
  purpose. 
  Mr. 
  

   C. 
  E. 
  P. 
  Brooks 
  has 
  of 
  late 
  years 
  (1922) 
  published 
  a 
  very 
  valuable 
  

   and 
  suggestive 
  little 
  book, 
  The 
  Evolution 
  of 
  Climate, 
  which 
  is 
  

   devoted 
  to 
  this 
  thesis. 
  Professor 
  Berry, 
  from 
  a 
  study 
  of 
  the 
  fossil 
  

   floras 
  of 
  North 
  America, 
  reaches 
  the 
  same 
  conclusion, 
  as 
  does 
  sub- 
  

   stantially 
  Professor 
  Ramsey, 
  of 
  Helsingfors, 
  who 
  published 
  his 
  

   observations 
  and 
  deductions 
  in 
  volume 
  64 
  of 
  the 
  Geological 
  Maga- 
  

   zine. 
  To 
  say 
  the 
  least, 
  it 
  is 
  a 
  remarkable 
  coincidence 
  that 
  so 
  many 
  

   and 
  so 
  widely 
  separated 
  investigators 
  should 
  have 
  reached 
  the 
  same 
  

   conclusion 
  from 
  somewhat 
  different 
  kinds 
  of 
  evidence. 
  In 
  his 
  lately 
  

   published 
  book, 
  The 
  Earth, 
  its 
  Origin, 
  History, 
  and 
  Physical 
  Consti- 
  

   tution 
  (1924), 
  Dr. 
  Harold 
  Jeffreys, 
  of 
  Cambridge, 
  devotes 
  a 
  con- 
  

   siderable 
  part 
  of 
  the 
  appendix 
  on 
  " 
  Theories 
  of 
  climatic 
  variation 
  " 
  

   to 
  an 
  examination 
  and 
  criticism 
  of 
  the 
  work 
  of 
  Brooks. 
  It 
  will 
  serve 
  

   our 
  purpose 
  excellently 
  to 
  quote 
  a 
  few 
  extracts 
  from 
  Jeffreys' 
  review 
  : 
  

  

  In 
  this 
  way 
  Brooks 
  is 
  able 
  to 
  show 
  that 
  more 
  oceanic 
  conditions, 
  which 
  

   actually 
  existed, 
  are 
  quantitatively 
  able 
  to 
  account 
  for 
  the 
  mild 
  climate 
  of 
  

   the 
  Eocene 
  period. 
  A 
  general 
  elevation 
  of 
  the 
  land 
  proceeded 
  throughout 
  the 
  

   Tertiary 
  era, 
  and 
  when 
  the 
  Scandanavian 
  highlands 
  and 
  the 
  Rocky 
  Mountains 
  

   reached 
  the 
  snow 
  line 
  an 
  ice 
  sheet 
  commenced 
  to 
  form. 
  * 
  * 
  * 
  The 
  actual 
  

   events 
  during 
  the 
  glacial 
  period 
  and 
  afterwards 
  agree 
  closely 
  with 
  Brooks's 
  

   inferences. 
  In 
  particular, 
  some 
  sand 
  dunes 
  in 
  north 
  Germany, 
  formed 
  at 
  this 
  

   time, 
  have 
  their 
  tips 
  pointing 
  to 
  the 
  west 
  instead 
  of 
  the 
  east, 
  showing 
  that 
  

   the 
  prevailing 
  wind 
  there 
  at 
  the 
  time 
  was 
  from 
  the 
  east. 
  This 
  is 
  exactly 
  what 
  

   would 
  be 
  expected 
  from 
  the 
  presence 
  of 
  the 
  Scandanavian 
  ice 
  sheet, 
  which 
  

   would 
  produce 
  * 
  * 
  * 
  east 
  winds 
  over 
  Germany. 
  In 
  many 
  other 
  parts 
  of 
  

   the 
  world 
  striking 
  agreements 
  are 
  found. 
  * 
  * 
  * 
  Brooks's 
  theory 
  is, 
  there- 
  

   fore, 
  a 
  very 
  substantial 
  contribution 
  to 
  our 
  understanding 
  of 
  climatic 
  change 
  ; 
  

   but 
  it 
  does 
  not 
  furnish 
  a 
  complete 
  explanation. 
  * 
  * 
  * 
  It 
  appears 
  as 
  if 
  the 
  

   later 
  stages, 
  at 
  least, 
  of 
  the 
  elevation 
  of 
  the 
  mountains 
  took 
  place 
  under 
  con- 
  

   ditions 
  when 
  the 
  snowfall 
  was 
  inappreciable, 
  and 
  that 
  the 
  ice 
  sheet 
  did 
  not 
  

   begin 
  to 
  form 
  until 
  some 
  further 
  change 
  of 
  climate, 
  not 
  attributable 
  to 
  the 
  

   mountains, 
  had 
  supervened. 
  The 
  Cambrian, 
  Ordovician, 
  and 
  Silurian 
  folds, 
  

   again, 
  must 
  have 
  raised 
  mountains 
  quite 
  comparable 
  to 
  those 
  of 
  the 
  Tertiary, 
  

   but 
  do 
  not 
  appear 
  to 
  have 
  been 
  followed 
  by 
  glaciation 
  on 
  anything 
  like 
  the 
  

   same 
  scale, 
  again 
  suggesting 
  that 
  mountain 
  formation, 
  though 
  it 
  may 
  be 
  a 
  

   necessary 
  preliminary 
  to 
  glaciation, 
  is 
  not 
  a 
  suflBcient 
  condition 
  for 
  it.^ 
  

  

  An 
  elaboration 
  of 
  this 
  same 
  conception 
  sees 
  in 
  the 
  many 
  climatic 
  

   fluctuations 
  of 
  the 
  Pleistocene 
  an 
  isostatic 
  response 
  of 
  the 
  earth's 
  

   crust 
  to 
  the 
  load 
  imposed 
  on 
  it 
  by 
  the 
  immense 
  accumulations 
  of 
  ice. 
  

   The 
  ice 
  sheets 
  were 
  established, 
  it 
  is 
  supposed, 
  when 
  the 
  continents 
  

   had 
  riseni 
  to 
  a 
  high 
  level, 
  and 
  under 
  the 
  enormous 
  load 
  of 
  ice 
  they 
  

   again 
  sank 
  to 
  an 
  altitude 
  at 
  which 
  the 
  ice 
  melted 
  and 
  snowfall 
  was 
  

   no 
  longer 
  sufficient 
  to 
  maintain 
  the 
  ice 
  caps. 
  Freed 
  from 
  its 
  load, 
  

   the 
  land 
  again 
  rose 
  td 
  a 
  height 
  at 
  which 
  the 
  ice 
  was 
  again 
  formed, 
  

   only 
  to 
  sink 
  once 
  more 
  under 
  the 
  renewed 
  load. 
  

  

  » 
  Jeffreys 
  : 
  Op. 
  cit. 
  p. 
  265. 
  

  

  