﻿Fossils 
  in 
  strata 
  of 
  Carboniferous 
  Age. 
  99 
  

  

  The 
  contrast 
  between 
  the 
  Nevada 
  and 
  the 
  Arkansas 
  sequence 
  

   is 
  seen 
  in 
  the 
  fact 
  that 
  in 
  the 
  Arkansas 
  section, 
  the 
  faunas 
  

   above 
  and 
  below 
  the 
  Spring 
  Creek 
  limestone 
  are 
  typically 
  

   Carboniferous 
  and 
  do 
  not 
  present 
  admixture 
  of 
  Devonian 
  

   forms, 
  while 
  the 
  Nevada 
  and, 
  from 
  present 
  reports 
  also, 
  the 
  

   California 
  sections 
  from 
  Devonian 
  far 
  into 
  Carboniferous 
  time 
  

   present 
  remarkable 
  commingling 
  of 
  Devonian 
  with 
  Carbonif- 
  

   erous 
  types. 
  The 
  3000 
  feet 
  of 
  conglomerate 
  in 
  Nevada, 
  re- 
  

   ported 
  by 
  Walcott 
  as 
  separating 
  the 
  White 
  Pine 
  shale 
  from 
  

   the 
  Carboniferous 
  limestone 
  with 
  Rhynchonella 
  Eurekensis, 
  

   suggests 
  the 
  cause 
  of 
  the 
  appearance 
  of 
  this 
  western 
  fauna 
  in 
  

   the 
  Arkansas 
  region, 
  i. 
  e. 
  an 
  elevation 
  of 
  the 
  western 
  area 
  

   sufficient 
  to 
  cause 
  diversion 
  of 
  the 
  ocean 
  currents 
  and 
  shifting 
  

   of 
  such 
  species 
  as 
  endured 
  the 
  transport 
  into 
  the 
  Mississippi 
  

   Valley 
  area. 
  In 
  the 
  Appalachian 
  province 
  the 
  Devonian 
  

   species 
  are 
  still 
  more 
  sharply 
  distinct 
  from 
  the 
  Carboniferous 
  

   forms 
  than 
  in 
  the 
  Mississippi 
  Valley. 
  

  

  These 
  are 
  the 
  facts 
  in 
  the 
  case 
  : 
  in 
  northwestern 
  Arkansas 
  

   is 
  found 
  a 
  fauna 
  in 
  the 
  Spring 
  Creek 
  limestone 
  which 
  by 
  its 
  

   stratigraphical 
  position 
  and 
  general 
  fossil 
  contents 
  is 
  shown 
  to 
  

   be 
  of 
  Carboniferous 
  age, 
  separated 
  by 
  at 
  least 
  two 
  well 
  defined 
  

   and 
  distinct 
  faunas 
  (the 
  Kinderhook-Chouteau 
  and 
  the 
  Bur- 
  

   lington-Keokuk) 
  from 
  the 
  latest 
  Devonian 
  fauna 
  of 
  the 
  Missis- 
  

   sippi 
  basin 
  province, 
  but 
  containing 
  several 
  species 
  which 
  in 
  

   the 
  more 
  eastern 
  Paleozoic 
  sections 
  are, 
  both 
  specifically 
  and 
  

   subgenerically, 
  Devonian 
  forms. 
  

  

  One 
  of 
  the 
  species 
  is 
  known 
  only 
  from 
  a 
  Carboniferous 
  

   horizon 
  of 
  the 
  western 
  part 
  of 
  the 
  continent, 
  and 
  others 
  are 
  

   distinctive 
  of 
  more 
  western 
  faunas 
  in 
  which 
  the 
  comming- 
  

   ling 
  of 
  Devonian 
  and 
  Carboniferous 
  species 
  is 
  conspicuous. 
  

  

  The 
  recurrence 
  of 
  the 
  Devonian 
  species 
  in 
  the 
  Arkansas 
  

   Carboniferous 
  rocks 
  is 
  most 
  readily 
  explained 
  as 
  a 
  case 
  of 
  

   migration 
  of 
  species 
  from 
  a 
  region 
  in 
  which 
  they 
  had 
  con- 
  

   tinued 
  to 
  live 
  unchanged, 
  into 
  a 
  region 
  from 
  which 
  they 
  had 
  

   for 
  a 
  long 
  time 
  been 
  absent 
  or 
  into 
  which 
  they 
  had 
  never 
  be- 
  

   fore 
  entered. 
  It 
  is 
  an 
  example 
  of 
  the 
  living 
  on 
  of 
  species 
  in 
  

   one 
  locality 
  long 
  after 
  they 
  had 
  become 
  extinct 
  or 
  were 
  replaced 
  

   by 
  other 
  species 
  in 
  another 
  region. 
  This 
  is 
  not 
  an 
  anomalous 
  

   fact 
  ; 
  the 
  Australian 
  land 
  fauna 
  is 
  a 
  remarkable 
  illustration 
  

   of 
  the 
  same 
  law. 
  Deep 
  sea 
  dredg4ngs 
  have 
  shown 
  the 
  same 
  

   fact 
  in 
  regard 
  to 
  some 
  of 
  the 
  abyssal 
  species 
  which 
  are 
  of 
  

   Eocene 
  or 
  Cretaceous 
  type, 
  ancient 
  characters 
  having 
  been 
  pre- 
  

   served 
  in 
  the 
  ocean 
  depths 
  while 
  they 
  have 
  been 
  superseded 
  

   by 
  evolved 
  successors 
  in 
  other 
  environments. 
  But 
  the 
  inter- 
  

   esting 
  point 
  in 
  this 
  Arkansas 
  case 
  is 
  that 
  we 
  have 
  here 
  a 
  sug- 
  

   gestion 
  as 
  to 
  the 
  cause 
  of 
  the 
  unchanged 
  continuance 
  of 
  the 
  

   species. 
  The 
  recurrent 
  Devonian 
  species 
  were 
  evidently 
  asso- 
  

  

  