﻿294 
  W. 
  H. 
  Twenhofel 
  — 
  The 
  Comanchean 
  and 
  

  

  2., 
  Kiowa 
  invasion 
  of 
  the 
  sea, 
  and 
  deposition 
  of 
  the 
  

   Kiowa 
  -Medicine 
  formations. 
  

  

  a. 
  Advance 
  of 
  the 
  sea 
  to 
  a 
  little 
  north 
  of 
  the 
  city 
  of 
  

   Salina, 
  Kansas. 
  

  

  b. 
  Eetreat 
  of 
  the 
  shore-line 
  toward 
  southern 
  Kan- 
  

   sas 
  with 
  terrestrial 
  deposition 
  over 
  the 
  central 
  part 
  of 
  

   the 
  state. 
  

  

  c. 
  Beadvance 
  of 
  the 
  shore-line 
  to 
  beyond 
  Salina, 
  

   Kansas. 
  

  

  d. 
  Eetreat 
  of 
  the 
  shore-line 
  toward 
  southern 
  Kan- 
  

   sas, 
  with 
  renewed 
  terrestrial 
  deposition 
  over 
  the 
  cen- 
  

   tral 
  part 
  of 
  the 
  state. 
  

  

  e. 
  Advance 
  of 
  the 
  shore-line 
  to 
  central 
  Kansas, 
  

   forming 
  the 
  marine 
  shell 
  bed 
  of 
  the 
  Upper 
  Dakota. 
  

  

  /. 
  Eetreat 
  southward, 
  with 
  renewed 
  terrestrial 
  de- 
  

   position 
  over 
  the 
  central 
  portion 
  of 
  the 
  state. 
  

  

  g. 
  Two 
  rapid 
  advances 
  of 
  the 
  sea 
  (perhaps 
  only 
  

   one), 
  separated 
  by 
  a 
  short 
  retreat, 
  one 
  of 
  the 
  advances 
  

   progressing 
  as 
  far 
  north 
  as 
  southern 
  South 
  Dakota. 
  

  

  3. 
  Eetreat 
  of 
  the 
  Comanchean 
  sea 
  as 
  far 
  south 
  as 
  

   Texas, 
  possibly 
  followed 
  by 
  erosion 
  of 
  the 
  plain 
  of 
  con- 
  

   struction. 
  

  

  4. 
  Invasion 
  of 
  the 
  Eagle 
  Ford-Benton 
  sea, 
  and 
  depo- 
  

   sition 
  of 
  the 
  initial 
  beds 
  of 
  the 
  Cretaceous. 
  

  

  The 
  Base 
  of 
  the 
  Cretaceous. 
  

  

  Some 
  have 
  insisted 
  that 
  the 
  Lower 
  Cretaceous 
  or 
  

   Comanchean 
  of 
  this 
  continent 
  has 
  the 
  value 
  of 
  one 
  sys- 
  

   tem 
  and 
  that 
  the 
  Upper 
  Cretaceous 
  represents 
  another. 
  

   If 
  so, 
  where 
  shall 
  the 
  base 
  of 
  the 
  Upper 
  Cretaceous 
  be 
  

   drawn? 
  There 
  was 
  most 
  certainly 
  an 
  extensive 
  retire- 
  

   ment 
  of 
  the 
  sea 
  at 
  the 
  close 
  of 
  the 
  Washita 
  and 
  there 
  

   are 
  considerable 
  differences 
  between 
  the 
  faunas 
  of 
  the 
  

   "Washita 
  and 
  those 
  of 
  the 
  Benton. 
  It 
  therefore 
  would 
  

   appear 
  that 
  the 
  place 
  to 
  draw 
  the 
  plane 
  between 
  the 
  

   Lower 
  and 
  Upper 
  Cretaceous 
  should 
  be 
  in 
  the 
  10 
  to 
  20 
  

   feet 
  of 
  strata 
  which 
  separate 
  the 
  last 
  appearance 
  of 
  the 
  

   "Washita 
  fauna 
  from 
  the 
  first 
  appearance 
  of 
  the 
  Benton. 
  

   So 
  far 
  as 
  Kansas, 
  Nebraska 
  and 
  Oklahoma 
  are 
  concerned, 
  

   the 
  plane 
  indicated 
  appears 
  to 
  be 
  the 
  only 
  place 
  where 
  

   such 
  a 
  line 
  of 
  separation 
  can 
  be 
  drawn. 
  Many 
  European 
  

   students 
  have 
  correlated 
  the 
  Washita 
  with 
  the 
  Cenoma- 
  

  

  