﻿Geology 
  and 
  Natural 
  History. 
  77 
  

  

  The 
  reader 
  should 
  also 
  be 
  reminded 
  that 
  in 
  most 
  of 
  these 
  

   Eocene 
  formations 
  of 
  the 
  Rocky 
  Mountains 
  occur 
  dinosaur 
  bones 
  

   of 
  unmistakable 
  Cretaceous 
  types. 
  In 
  other 
  words, 
  that 
  while 
  

   the 
  moist 
  and 
  warm 
  climate 
  is 
  said 
  to 
  have 
  prevailed, 
  the 
  dino- 
  

   saurs, 
  supposed 
  to 
  be 
  more 
  sensitive 
  to 
  environmental 
  change, 
  

   did 
  not 
  die 
  out 
  or 
  change 
  markedly, 
  while 
  the 
  plants 
  underwent 
  

   not 
  only 
  a 
  specific 
  but 
  as 
  well 
  a 
  distinct 
  generic 
  change! 
  How 
  

   these 
  two 
  sets 
  of 
  facts 
  are 
  to 
  be 
  harmonized 
  is 
  as 
  yet 
  not 
  at 
  all 
  

   clear. 
  Seemingly 
  the 
  dinosaur 
  evidence 
  still 
  negates 
  the 
  inter- 
  

   pretation 
  placed 
  on 
  the 
  importance 
  of 
  the 
  unconformity 
  between 
  

   the 
  Vermejo 
  and 
  Eaton 
  and 
  related 
  formations. 
  On 
  the 
  other 
  

   hand, 
  the 
  student 
  of 
  marine 
  invertebrates 
  is 
  also 
  puzzled 
  to 
  see 
  

   why 
  the 
  earliest 
  Eocene 
  floras 
  of 
  the 
  Rocky 
  Mountain 
  area, 
  with 
  

   their 
  Cretaceous 
  dinosaurs, 
  are 
  not 
  markedly 
  those 
  of 
  the 
  oldest 
  

   Tertiary 
  but 
  are 
  decidedly 
  those 
  of 
  the 
  Middle 
  Eocene 
  or 
  Wilcox 
  

   time. 
  In 
  this 
  connection 
  the 
  student 
  will 
  not 
  fail 
  to 
  notice 
  that 
  

   there 
  is 
  a 
  very 
  long 
  time 
  break 
  between 
  the 
  Cretaceous 
  and 
  the 
  

   Midway 
  of 
  the 
  Atlantic-Gulf 
  area. 
  Not 
  a 
  single 
  marine 
  inverte- 
  

   brate 
  other 
  than 
  Protozoa 
  is 
  known 
  to 
  cross 
  this 
  stratigraphic 
  

   line, 
  and 
  these 
  animals 
  are 
  supposed 
  to 
  be 
  less 
  subject 
  in 
  their 
  

   evolution 
  to 
  climatic 
  change 
  than 
  are 
  the 
  land-living 
  ones. 
  Yet 
  

   the 
  highly 
  specialized 
  dinosaurs 
  of 
  the 
  Cretaceous 
  are 
  said 
  to 
  

   have 
  continued 
  alive 
  into 
  the 
  Middle 
  Eocene 
  with 
  not 
  more 
  than 
  

   specific 
  change. 
  These 
  are 
  some 
  of 
  the 
  facts 
  that 
  still 
  fail 
  of 
  

   being 
  harmonized 
  into 
  an 
  agreeable 
  chronogenesis, 
  an 
  agreement 
  

   as 
  to 
  when 
  the 
  Mesozoic 
  closed 
  and 
  the 
  Tertiary 
  began 
  in 
  North 
  

   America/ 
  

  

  The 
  paleobotanists 
  have 
  seemingly 
  gone 
  as 
  far 
  toward 
  the 
  

   solution 
  of 
  this 
  vexed 
  problem 
  as 
  their 
  material 
  permits, 
  and 
  it 
  

   amounts 
  to 
  more 
  than 
  1000 
  species 
  from 
  a 
  continent-wide 
  area. 
  

   On 
  the 
  other 
  hand, 
  one 
  wonders 
  if 
  a 
  restudy 
  of 
  the 
  dinosaurs 
  

   in 
  the 
  light 
  of 
  the 
  present 
  far 
  more 
  detailed 
  stratigraphy 
  would 
  

   show 
  that 
  our 
  biologic 
  and 
  geologic 
  knowledge 
  of 
  them 
  is 
  faulty 
  

   and 
  that 
  they 
  too 
  have 
  undergone 
  a 
  specific 
  and 
  generic 
  evolution 
  

   comparable 
  to 
  that 
  of 
  the 
  plants. 
  That 
  the 
  dinosaurs 
  may 
  have 
  

   lived 
  on 
  into 
  Eocene 
  time 
  in 
  the 
  Cretaceous 
  of 
  the 
  Rocky 
  Moun- 
  

   tain 
  area 
  is 
  understandable 
  when 
  we 
  are 
  told 
  by 
  the 
  paleobotan- 
  

   ists 
  that 
  there 
  was 
  no 
  appreciable 
  climatic 
  change 
  during 
  the 
  

   close 
  of 
  the 
  Mesozoic 
  and 
  early 
  in 
  Tertiary 
  time. 
  Yet 
  the 
  flora 
  

   changed 
  completely 
  and 
  it 
  is 
  in 
  this 
  that 
  our 
  difficulties 
  lie. 
  The 
  

   climatic 
  and 
  as 
  well 
  the 
  physiographic 
  change 
  came 
  after 
  Raton- 
  

   Denver-Fort 
  Union, 
  etc. 
  time, 
  as 
  is 
  seen 
  in 
  the 
  presence 
  of 
  the 
  

   tillites 
  in 
  southwestern 
  Colorado, 
  and 
  with 
  the 
  introduction 
  of 
  

   this 
  change 
  the 
  dinosaurs 
  vanished. 
  Finally, 
  we 
  need 
  more 
  light 
  

   as 
  to 
  the 
  length 
  of 
  the 
  "lost 
  interval" 
  between 
  the 
  Cretaceous 
  

   and 
  the 
  Midway 
  of 
  the 
  Atlantic 
  border, 
  and 
  if 
  possible, 
  correla- 
  

   tions 
  based 
  on 
  animal 
  remains 
  between 
  the 
  older 
  Tertiary 
  of 
  the 
  

   Atlantic-Gulf 
  area 
  and 
  those 
  of 
  the 
  Cenozoic 
  of 
  the 
  Paris 
  basin. 
  

  

  