﻿FOSSIL 
  MARINE 
  FAUNAS 
  AS 
  INDICATORS 
  OF 
  

   CLIMATIC 
  CONDITIONS^ 
  

  

  By 
  Edwin 
  Kirk 
  

   TJ. 
  8. 
  Geological 
  Survey 
  

  

  Since 
  the 
  conception 
  of 
  an 
  earth 
  gradually 
  and 
  appreciably 
  cool- 
  

   ing 
  within 
  the 
  space 
  of 
  geologically 
  recorded 
  time 
  has 
  been 
  changed 
  

   so 
  radically, 
  a 
  great 
  deal 
  of 
  interest 
  has 
  been 
  manifested 
  in 
  collecting 
  

   evidence 
  as 
  to 
  what 
  the 
  climates 
  of 
  the 
  past 
  may 
  actually 
  have 
  been 
  

   like. 
  No 
  longer 
  do 
  we 
  vision 
  the 
  tepid 
  waters 
  and 
  steaming 
  air 
  of 
  

   the 
  Carboniferous 
  swamps 
  pictured 
  in 
  the 
  geologies 
  of 
  a 
  generation 
  

   ago. 
  Rather 
  we 
  think 
  of 
  that 
  widespread 
  glaciation 
  of 
  the 
  Permian 
  

   or 
  upper 
  Carboniferous 
  and 
  the 
  constantly 
  augumented 
  series 
  of 
  

   glaciations 
  reaching 
  down 
  from 
  the 
  pre-Cambrian 
  to 
  the 
  present. 
  

   To 
  be 
  sure, 
  most 
  of 
  us 
  are 
  subconsciously 
  superimposing 
  these 
  glacial 
  

   periods 
  on 
  a 
  mental 
  background 
  consisting 
  of 
  a 
  warm 
  genial 
  world 
  

   and 
  warm 
  oceans. 
  They 
  are 
  therefore 
  incomprehensible 
  anomalies, 
  

   only 
  to 
  be 
  explained 
  by 
  fundamental 
  changes 
  such 
  as 
  shifted 
  poles, 
  

   reversed 
  oceanic 
  currents, 
  or 
  similar 
  abnormal 
  conditions. 
  We 
  have, 
  

   it 
  is 
  true, 
  indubitable 
  evidence 
  that 
  secvdar 
  changes 
  of 
  climate 
  have 
  

   taken 
  place, 
  but 
  one 
  who 
  chose 
  could 
  well 
  argue 
  that 
  we 
  have 
  no 
  

   conclusive 
  proof 
  that 
  the 
  mean 
  annual 
  atmospheric 
  temperature 
  at 
  

   sea 
  level 
  or 
  the 
  mean 
  temperature 
  of 
  our 
  oceanic 
  waters 
  has 
  changed 
  

   notably 
  during 
  recorded 
  time. 
  Changes 
  in 
  elevation 
  and 
  in 
  the 
  

   relative 
  distribution 
  of 
  land 
  and 
  water, 
  with 
  the 
  imjjortant 
  corollary 
  

   of 
  changed 
  oceanic 
  currents, 
  may 
  well 
  account 
  for 
  the 
  climates 
  of 
  

   the 
  past, 
  as 
  has 
  been 
  ably 
  advocated 
  by 
  manj'^ 
  geologists 
  from 
  Lyell 
  

   to 
  the 
  present. 
  The 
  purpose 
  of 
  the 
  present 
  paper 
  is 
  not 
  to 
  controvert 
  

   any 
  one 
  of 
  the 
  multitudinous 
  speculations 
  in 
  regard 
  to 
  the 
  climates 
  of 
  

   the 
  past 
  but 
  briefly 
  to 
  submit 
  a 
  few 
  facts 
  in 
  regard 
  to 
  one 
  line 
  of 
  

   evidence 
  used 
  by 
  the 
  majority 
  of 
  the 
  speculators. 
  

  

  Among 
  most 
  of 
  the 
  writers 
  so 
  vividly 
  depicting 
  the 
  equable 
  climates 
  

   widely 
  prevailing 
  during 
  the 
  Paleozoic 
  the 
  widespread 
  invertebrate 
  

   faunas 
  of 
  the 
  ancient 
  seas 
  offer 
  a 
  most 
  conclusive 
  argument 
  for 
  warm 
  

   ubiquitous 
  shallow 
  seas 
  and 
  an 
  accompanying 
  world-wide 
  sub- 
  

  

  ^ 
  Published 
  by 
  permission 
  of 
  the 
  Director, 
  U. 
  S. 
  Geological 
  Survey. 
  

  

  299 
  

  

  