﻿Keyes 
  — 
  Carboniferous 
  and 
  Devonian 
  Strata. 
  

  

  161 
  

  

  The 
  stratigraphic 
  relations 
  of 
  the 
  several 
  terranes 
  are 
  best 
  

   shown 
  in 
  cross-section 
  as 
  they 
  are 
  plotted 
  along 
  the 
  line 
  of 
  the 
  

   Mississippi 
  river 
  from 
  Louisiana, 
  Missouri, 
  to 
  Muscatine, 
  Iowa 
  

  

  (%• 
  i). 
  

  

  Detailed 
  vertical 
  sections 
  I 
  have 
  given 
  in 
  another 
  place.* 
  At 
  

   this 
  time 
  the 
  shales 
  lying 
  at 
  the 
  base 
  of 
  the 
  Louisiana 
  limestone 
  

   were 
  little 
  considered, 
  since 
  at 
  the 
  

   town 
  of 
  Louisiana 
  they 
  were 
  only 
  two 
  

   feet 
  thick 
  and 
  the 
  northern 
  local- 
  

   ities 
  were 
  not 
  yet 
  carefully 
  studied. 
  f 
  

   Comparisons 
  of 
  the 
  Iowa 
  and 
  Mis- 
  

   souri 
  sections 
  are 
  made 
  in 
  the 
  report 
  

   on 
  the 
  geology 
  of 
  Des 
  Moines 
  

   county. 
  J 
  At 
  one 
  time§ 
  it 
  seemed 
  

   that 
  upon 
  faunal 
  grounds 
  the 
  Kin- 
  

   derhook 
  shales 
  as 
  exposed 
  at 
  Louis- 
  

   iana 
  could 
  just 
  as 
  well 
  be 
  included 
  

   in 
  the 
  Devonian 
  section, 
  but 
  this 
  old 
  

   view 
  long 
  since 
  gave 
  way 
  to 
  the 
  

   stratigraphic 
  evidence. 
  

  

  The 
  Chouteau 
  limestone 
  is 
  quite 
  

   thin 
  on 
  the 
  Mississippi 
  river, 
  but 
  

   rapidly 
  becomes 
  thicker 
  to 
  the 
  west- 
  

   ward. 
  At 
  Louisiana 
  the 
  Hannibal 
  

   shales 
  are 
  75 
  feet 
  thick 
  ; 
  at 
  Keokuk, 
  

   65 
  feet 
  ; 
  at 
  Burlington 
  about 
  50 
  feet 
  

   of 
  the 
  blue 
  shales 
  in 
  the 
  base 
  of 
  the 
  

   river-bluffs 
  are 
  assignable 
  here. 
  The 
  

   Louisiana 
  limestone, 
  which 
  is 
  50 
  feet 
  

   thick 
  at 
  the 
  type-locality, 
  becomes 
  

   gradually 
  thinner 
  northward, 
  until 
  

   at 
  Keokuk 
  it 
  is 
  only 
  10 
  feet 
  in 
  thick- 
  

   ness, 
  and 
  soon 
  vanishes 
  altogether 
  as 
  

   shown 
  by 
  well-sections. 
  This 
  per- 
  

   mits 
  the 
  overlying 
  and 
  underlying 
  

   shales 
  of 
  Missouri 
  to 
  come 
  together 
  

   in 
  Iowa 
  and 
  form 
  one 
  continuous 
  

   shale- 
  section. 
  

  

  Immediately 
  beneath 
  the 
  Louis- 
  

   iana 
  limestone 
  at 
  the 
  original 
  locality 
  

   are 
  two 
  feet 
  of 
  blue 
  shales. 
  This 
  ap- 
  

   parently 
  insignificant 
  layer 
  is 
  usually 
  

   included 
  in 
  the 
  Grassy 
  black 
  shales 
  

   below. 
  I 
  It 
  now 
  seems 
  to 
  have 
  much 
  

   greater 
  importance. 
  Northward 
  

  

  * 
  Bull. 
  Geol.Soc. 
  America, 
  vol. 
  iii, 
  p. 
  283,1892. 
  

   f 
  American 
  Geologist, 
  vol. 
  x, 
  p. 
  384, 
  1892. 
  

   % 
  Iowa 
  Geol. 
  Surv., 
  vol. 
  iii 
  p. 
  436, 
  1894. 
  

   § 
  Trans. 
  St. 
  Louis 
  Acad. 
  Sei., 
  vol. 
  vii, 
  p. 
  369, 
  

  

  1897. 
  

   || 
  Proc. 
  Iowa 
  Acad. 
  Sci., 
  vol. 
  v, 
  p. 
  66, 
  1898. 
  

  

  Fig. 
  1. 
  Geologic 
  cross-sec- 
  

   tion 
  along 
  Mississippi 
  River. 
  

  

  