﻿Twenhofel 
  — 
  Wreford 
  and 
  Foraker 
  Limestones. 
  429 
  

  

  destroyed. 
  If 
  these 
  nodules 
  are 
  of 
  algal 
  origin, 
  they 
  

   were 
  probably 
  calcareous 
  in 
  the 
  beginning 
  and 
  were 
  sub- 
  

   sequently 
  changed 
  to 
  chert 
  by 
  replacement. 
  

  

  Resume 
  of 
  Facts 
  and 
  Conclusions 
  

  

  1. 
  The 
  cherts 
  of 
  the 
  Foraker 
  and 
  Wreford 
  limestones 
  

   in 
  the 
  outcrops 
  in 
  the 
  vicinity 
  of 
  the 
  state 
  line 
  of 
  Kansas 
  

   and 
  Oklahoma 
  are 
  quite 
  varied 
  in 
  character 
  and 
  the 
  dif- 
  

   ferent 
  varieties 
  are 
  confined 
  to 
  distinct 
  zones 
  of 
  wide 
  

   horizontal 
  distribution. 
  

  

  2. 
  The 
  observed 
  facts 
  do 
  not 
  harmonize 
  with 
  theories 
  

   postulating 
  an 
  origin 
  for 
  these 
  cherts 
  consequential 
  to 
  

   weathering, 
  or 
  one 
  of 
  replacement, 
  or 
  of 
  cavity-filling 
  in 
  

   solid 
  rocks. 
  It 
  is 
  not 
  disputed, 
  however, 
  that 
  chert 
  

   develops 
  in 
  such 
  ways. 
  

  

  3. 
  It 
  is 
  possible 
  that 
  these 
  cherts 
  developed 
  through 
  

   direct 
  precipitation 
  of 
  silica 
  in 
  solution 
  in 
  the 
  sea 
  water, 
  

   but 
  it 
  is 
  not 
  believed 
  that 
  the 
  facts 
  support 
  such 
  an 
  origin. 
  

   That 
  some 
  silica 
  may 
  have 
  been 
  added 
  to 
  the 
  nodules 
  

   from 
  silica 
  in 
  solution 
  in 
  the 
  sea 
  water 
  is 
  considered 
  

   quite 
  possible. 
  

  

  4. 
  The 
  chert 
  is 
  believed 
  in 
  major 
  part 
  to 
  have 
  resulted 
  

   from 
  replacement 
  of 
  unconsolidated 
  limestone, 
  the 
  silica 
  

   being 
  derived 
  from 
  silica 
  in 
  solution 
  which 
  was 
  mingled 
  

   with 
  the 
  sediments, 
  from 
  silica 
  in 
  solution 
  in 
  the 
  sea 
  

   water, 
  and 
  from 
  solution 
  of 
  organic 
  or 
  other 
  silica, 
  or 
  sili- 
  

   cates 
  deposited 
  in 
  some 
  form 
  with 
  the 
  sediments. 
  

  

  5. 
  The 
  suggestion 
  is 
  made 
  that 
  the 
  banded 
  nodules 
  

   occurring 
  in 
  one 
  of 
  the 
  zones 
  may 
  have 
  had 
  an 
  algal 
  

   origin, 
  but 
  no 
  microscopic 
  structures 
  similar 
  to 
  those 
  

   occurring 
  in 
  algae 
  have 
  been 
  found. 
  

  

  University 
  of 
  Wisconsin, 
  

   Madison, 
  Wis. 
  

  

  