﻿288 
  W. 
  H. 
  Ttvenhofel 
  — 
  The 
  Comanchean 
  and 
  

  

  The 
  strata 
  from 
  the 
  shale 
  bed 
  to 
  the 
  top 
  of 
  the 
  salif 
  er- 
  

   ous 
  zone 
  contain 
  deposits 
  which 
  were 
  probably 
  made 
  by 
  

   minor 
  backward 
  and 
  forward 
  movements 
  of 
  the 
  strand- 
  

   line. 
  The 
  beds 
  containing 
  marine 
  fossils 
  record 
  north- 
  

   ward 
  or 
  forward 
  movements. 
  The 
  nnfossiliferons 
  sands 
  

   and 
  mnds 
  record 
  southward 
  or 
  outgoing 
  movements 
  of 
  

   the 
  strand-line. 
  The 
  waters, 
  at 
  times, 
  were 
  evidently 
  

   strongly 
  concentrated. 
  

  

  The 
  lignite 
  zone, 
  where 
  present, 
  varies 
  in 
  thickness 
  

   from 
  about 
  6 
  to 
  26 
  inches. 
  In 
  some 
  localities 
  it 
  is 
  want- 
  

   ing, 
  and 
  it 
  is 
  not 
  certain 
  that 
  it 
  is 
  at 
  the 
  same 
  level 
  in 
  

   every 
  one 
  of 
  its 
  occurrences. 
  The 
  deposit 
  is 
  evidently 
  

   of 
  terrestrial 
  paludal 
  origin. 
  

  

  The 
  lower 
  Dakota 
  consists 
  of 
  red, 
  brown, 
  yellow 
  and 
  

   gray 
  quartz 
  sandstones 
  and 
  gray, 
  dark 
  and 
  brown 
  shales. 
  

   The 
  former 
  dominate 
  above, 
  the 
  latter 
  below. 
  The 
  

   sandstones 
  are 
  rough-bedded, 
  and 
  quite 
  commonly 
  cross- 
  

   laminated, 
  with 
  foresets 
  of 
  variable 
  steepness, 
  length 
  

   and 
  direction 
  of 
  inclination. 
  Some 
  levels 
  are 
  charac- 
  

   terized 
  by 
  the 
  abundant 
  presence 
  of 
  limonite 
  concretions 
  

   of 
  all 
  sorts 
  of 
  shapes. 
  At 
  different 
  localities 
  and 
  in 
  dif- 
  

   ferent 
  horizons 
  occur 
  splendidly 
  preserved 
  fossil 
  leaves 
  

   of 
  dicotyledons. 
  The 
  sequence 
  varies 
  greatly 
  from 
  place 
  

   to 
  place 
  and 
  the 
  writer 
  has 
  found 
  it 
  impossible 
  to 
  recog- 
  

   nize 
  any 
  horizon 
  beyond 
  the 
  limits 
  of 
  an 
  exposure. 
  Gra- 
  

   dation 
  from 
  shales 
  to 
  sandstones 
  is 
  extremely 
  common 
  

   in 
  parts 
  of 
  the 
  division. 
  If 
  a 
  section 
  be 
  measured 
  north 
  

   of 
  the 
  limits 
  of 
  the 
  lower 
  marine 
  strata 
  described 
  below, 
  

   it 
  is 
  certain 
  that 
  the 
  equivalents 
  of 
  some 
  of 
  the 
  latter 
  

   beds 
  will 
  be 
  included 
  in 
  the 
  Lower 
  Dakota. 
  There 
  is 
  

   great 
  variation 
  in 
  thickness 
  and 
  the 
  figure 
  given 
  is 
  

   merely 
  approximate. 
  

  

  The 
  character 
  of 
  the 
  Mentor 
  beds 
  is 
  best 
  shown 
  by 
  the 
  

   section 
  exposed 
  in 
  the 
  Natural 
  Corral 
  in 
  McPherson 
  

   County. 
  This 
  is 
  as 
  follows: 
  

  

  5. 
  Sandstone, 
  red 
  to 
  brown, 
  coarse 
  to 
  medium-grained, 
  locally 
  

   contains 
  many 
  of 
  the 
  concretions 
  which 
  are 
  character- 
  

   istic 
  of 
  the 
  "Dakota." 
  Where 
  these 
  are 
  greatly 
  devel- 
  

   oped, 
  the 
  fossils 
  are 
  absent; 
  but 
  where 
  concretions 
  are 
  

   few, 
  fossils 
  are 
  abundant. 
  Those 
  most 
  diagnostic 
  are: 
  

   Cardium 
  kansasense 
  Meek, 
  Trigonia 
  emoryi 
  Conrad, 
  

   Turrit 
  ella 
  salinaensis 
  Meek 
  (near 
  T. 
  seriatim-granulata) 
  . 
  

   These 
  serve 
  to 
  fix 
  the 
  Washita 
  age 
  of 
  the 
  stratum 
  8 
  feet 
  

  

  4. 
  Sandstones, 
  yellow, 
  well-assorted, 
  highly 
  cross-laminated, 
  

   probably 
  of 
  terrestrial 
  origin 
  26 
  feet 
  

  

  