﻿192 
  F. 
  H. 
  Knowlton 
  — 
  A 
  Dicotyledonous 
  Flora 
  

  

  In 
  the 
  complete 
  paper, 
  of 
  which 
  the 
  present 
  is 
  an 
  

   abstract, 
  I 
  have 
  given 
  a 
  revision 
  of 
  this 
  "Dakota 
  flora' 
  ' 
  

   of 
  the 
  Denver 
  Basin. 
  It 
  inclndes 
  21 
  species, 
  all 
  but 
  3 
  

   of 
  which 
  came 
  from 
  the 
  beds 
  of 
  Morrison. 
  It 
  further 
  

   develops 
  that 
  only 
  6 
  of 
  the 
  18 
  species 
  are 
  confined 
  to 
  the 
  

   beds 
  at 
  Morrison, 
  the 
  others 
  being 
  widely 
  distributed 
  

   in 
  the 
  Dakota, 
  Cheyenne, 
  Woodbine, 
  Earitan, 
  Magothy, 
  

   Bladen, 
  Eutaw, 
  Black 
  Creek, 
  Tuscaloosa, 
  etc. 
  

  

  In 
  attempting 
  to 
  interpret 
  the 
  relation 
  of 
  the 
  

   " 
  Dakota" 
  of 
  the 
  Denver 
  Basin 
  to 
  the 
  Dakota 
  in 
  the 
  

   type 
  area 
  as 
  well 
  as 
  other 
  areas 
  where 
  it 
  has 
  been 
  identi- 
  

   fied, 
  it 
  appears 
  that 
  several 
  views 
  are 
  possible. 
  The 
  

   type 
  area 
  for 
  the 
  Dakota 
  is 
  northeastern 
  Nebraska. 
  

   Here 
  the 
  Dakota 
  has 
  not 
  been 
  subdivided 
  and 
  is 
  followed 
  

   immediately 
  by 
  the 
  Benton. 
  In 
  southern 
  Kansas 
  the 
  

   leaf-bearing 
  Dakota 
  rests 
  on 
  the 
  marine 
  Kiowa 
  shale, 
  

   and 
  this 
  in 
  turn 
  on 
  the 
  Cheyenne 
  sandstone, 
  which 
  con- 
  

   tains 
  a 
  flora 
  that 
  certainly 
  has 
  much 
  in 
  common 
  with 
  

   the 
  overlying 
  Dakota. 
  At 
  Morrison 
  the 
  section 
  appears 
  

   to 
  be 
  similar 
  to 
  the 
  Kansas 
  section, 
  that 
  is, 
  the 
  Dakota 
  

   as 
  now 
  delimited 
  rests 
  on 
  the 
  shale 
  of 
  the 
  upper 
  part 
  of 
  

   the 
  Purgatoire 
  formation, 
  which 
  in 
  turn 
  is 
  underlain 
  by 
  

   the 
  sandstone 
  of 
  the 
  Purgatoire 
  — 
  the 
  so-called 
  lower 
  

   Dakota 
  which 
  contains 
  the 
  "Dakota 
  flora" 
  of 
  the 
  Mor- 
  

   rison 
  region. 
  

  

  Are 
  the 
  strata 
  at 
  Morrison 
  which 
  contain 
  similar 
  plant 
  

   forms 
  to 
  be 
  referred 
  to 
  separate 
  series? 
  Are 
  they 
  to 
  

   be 
  correlated 
  with 
  the 
  ordinary 
  leaf 
  -bearing 
  Dakota 
  of 
  

   the 
  Kansas 
  section 
  or 
  with 
  the 
  Cheyenne, 
  or 
  are 
  they 
  to 
  

   be 
  considered 
  as 
  a 
  group 
  with 
  the 
  three 
  units 
  (Dakota, 
  

   Kiowa, 
  and 
  Cheyenne) 
  as 
  formations! 
  The 
  data 
  avail- 
  

   able 
  are 
  perhaps 
  not 
  sufficient 
  to 
  permit 
  a 
  definite 
  answer 
  

   to 
  these 
  questions, 
  though 
  it 
  may 
  be 
  pointed 
  out 
  that 
  

   certain 
  observed 
  facts 
  of 
  stratigraphy 
  and 
  physiography 
  

   would 
  be 
  harmonized 
  or 
  rationalized 
  by 
  considering 
  the 
  

   Dakota 
  as 
  a 
  group 
  within 
  the 
  Upper 
  Cretaceous 
  and 
  

   embracing 
  the 
  several 
  units 
  as 
  formations. 
  This, 
  of 
  

   course, 
  involves 
  the 
  age 
  assignment 
  of 
  the 
  Cheyenne 
  

   sandstone. 
  As 
  already 
  pointed 
  out, 
  this 
  forms 
  a 
  part 
  

   of 
  the 
  "Washita 
  division 
  of 
  the 
  Comanche 
  series 
  that 
  has 
  

   usually 
  been 
  placed 
  by 
  American 
  geologists 
  at 
  the 
  top 
  

   of 
  the 
  Lower 
  Cretaceous. 
  But, 
  as 
  Berry 
  1 
  has 
  recently 
  

   pointed 
  out, 
  foreign 
  paleontologists 
  long 
  ago 
  indicated 
  

  

  1 
  Berry, 
  E. 
  W., 
  Maryland 
  Geol. 
  Survey, 
  Upper 
  Cretaceous, 
  text, 
  p. 
  222, 
  

   1916. 
  ' 
  * 
  

  

  