﻿Dakota 
  Strata 
  of 
  Kansas. 
  287 
  

  

  . 
  Shell 
  bed, 
  marine, 
  Washita 
  fauna 
  . 
  . 
  6 
  inches 
  

  

  Lignite 
  zone, 
  coastal 
  plain 
  terrestrial 
  6-26 
  inches 
  

  

  Shales, 
  terrestrial 
  ? 
  5 
  ± 
  feet 
  

  

  Lower 
  Dakota, 
  terrestrial, 
  "Dakota" 
  flora 
  250 
  ± 
  feet 
  

  

  Mentor 
  sandstone 
  bed, 
  marine, 
  Washita 
  fauna 
  8 
  feet 
  

  

  Sandstones 
  and 
  shales, 
  terrestrial, 
  "Dakota" 
  flora... 
  52 
  feet 
  

  

  Shell 
  bed, 
  marine, 
  Washita 
  fauna 
  2-3 
  feet 
  

  

  Shales, 
  terrestrial 
  ? 
  30 
  feet 
  

  

  The 
  gypsiferous 
  shales 
  consist 
  of 
  gray 
  to 
  dark 
  shales 
  

   interbedded 
  with 
  gray 
  and 
  red 
  sandstones. 
  Gypsum 
  

   crystals 
  and 
  impregnations 
  exist 
  pretty 
  generally 
  

   throughout. 
  There 
  are 
  also 
  thin 
  beds 
  of 
  gypsum. 
  So 
  

   far 
  as 
  the 
  writer 
  has 
  information, 
  no 
  fossils 
  have 
  been 
  

   identified 
  from 
  the 
  member, 
  but 
  logs 
  have 
  been 
  found 
  in 
  

   the 
  basal 
  Benton 
  which 
  Logan 
  considers 
  to 
  have 
  "un- 
  

   doubtedly 
  belonged 
  to 
  the 
  upper 
  Dakota 
  horizon. 
  " 
  13 
  

   The 
  sediments 
  which 
  formed 
  this 
  member 
  probably 
  

   developed 
  in 
  relic 
  lakes 
  left 
  by 
  the 
  retiring 
  Washita 
  sea. 
  

   The 
  climate 
  was 
  probably 
  of 
  such 
  a 
  character 
  that 
  the 
  

   concentration 
  increased 
  and 
  the 
  lakes 
  ultimately 
  disap- 
  

   peared 
  through 
  drying 
  up 
  or 
  filling 
  up 
  with 
  mud. 
  The 
  

   thickness 
  varies 
  from 
  10 
  to 
  20 
  feet. 
  

  

  The 
  saliferous 
  shales 
  are 
  of 
  gray 
  to 
  dark 
  colors 
  and 
  

   highly 
  impregnated 
  with 
  salt. 
  Interbedded 
  are 
  sand- 
  

   stone 
  layers 
  from 
  two 
  of 
  which 
  marine 
  fossils 
  have 
  been 
  

   collected. 
  Those 
  definitely 
  identified 
  by 
  Logan 
  are: 
  14 
  

   Arcopagella 
  macrodonta 
  Meek, 
  Cardium 
  kansasense 
  

   Meek, 
  Corbicula 
  subtrigonalis 
  Meek, 
  Crassatellina 
  ob- 
  

   long 
  a 
  Meek, 
  Gyrena 
  dakotensis 
  Meek, 
  Mactra 
  siouxensis 
  

   Meek, 
  Margaritana 
  nebraskensis 
  Meek, 
  Protocardia 
  soli- 
  

   naensis 
  Meek, 
  Tellina 
  modesta 
  Meek, 
  T. 
  subscitula 
  Meek, 
  

   Trigonarca 
  salinaensis 
  Meek, 
  Yoldia 
  microdonta 
  Meek. 
  

   Nearly 
  every 
  one 
  of 
  these 
  species 
  is 
  represented 
  by 
  iden- 
  

   tical 
  or 
  closely 
  related 
  forms 
  in 
  the 
  Mentor 
  beds 
  so 
  that 
  

   there 
  is 
  little 
  doubt 
  but 
  that 
  they 
  were 
  inhabitants 
  of 
  the 
  

   same 
  sea. 
  The 
  thickness 
  of 
  this 
  member 
  varies 
  from 
  15 
  

   to 
  30 
  feet. 
  

  

  From 
  the 
  shell 
  bed 
  which 
  is 
  only 
  about 
  6 
  inches 
  thick, 
  

   Logan 
  lists 
  : 
  14 
  Cardium 
  kansasense 
  Meek, 
  Leptosolen 
  

   conradi 
  Meek, 
  Pharella 
  dakotaensis 
  Meek. 
  It 
  is 
  pre- 
  

   ceded 
  by 
  shales 
  similar 
  to 
  those 
  of 
  the 
  saliferous 
  zone, 
  

   and 
  related 
  to 
  them 
  in 
  origin. 
  

  

  13 
  W. 
  N. 
  Logan, 
  Kansas 
  Univ., 
  Geol. 
  Surv., 
  2, 
  212, 
  1897. 
  

  

  14 
  W. 
  N. 
  Logan, 
  op. 
  cit., 
  pp. 
  207-212. 
  

  

  