﻿G. 
  R. 
  Mansfield 
  — 
  Formations 
  of 
  S.E. 
  Idaho. 
  399 
  

  

  Aet. 
  XXXI. 
  — 
  The 
  Wasatch 
  and 
  Salt 
  Lake 
  Formations 
  of 
  

   southeastern 
  Idaho; 
  by 
  George 
  Rogers 
  Mansfield. 
  1 
  

  

  Among 
  the 
  stratigraphic 
  problems 
  disclosed 
  by 
  the 
  

   Geological 
  Survey's 
  detailed 
  study 
  of 
  the 
  phosphate 
  beds 
  

   in 
  southeastern 
  Idaho 
  that 
  of 
  the 
  Tertiary 
  deposits 
  is 
  

   worthy 
  of 
  mention. 
  The 
  region 
  thus 
  far 
  studied 
  in- 
  

   cludes 
  the 
  Fort 
  Hall 
  Indian 
  Reservation 
  and 
  the 
  Mont- 
  

   pelier, 
  Slug 
  Creek, 
  Crow 
  Creek, 
  Lanes 
  Creek, 
  Freedom, 
  

   Henry 
  and 
  Cranes 
  Flat 
  quadrangles, 
  a 
  total 
  area 
  of 
  

   nearly 
  3,000 
  square 
  miles 
  ; 
  see 
  fig. 
  1. 
  

  

  Tertiary 
  system. 
  

  

  The 
  Tertiary 
  system 
  in 
  this 
  region 
  is 
  represented 
  by 
  

   patches 
  of 
  sediments 
  that 
  vary 
  greatly 
  in 
  texture, 
  thick- 
  

   ness, 
  character, 
  and 
  degree 
  of 
  consolidation 
  and 
  that 
  lie 
  

   unconformably 
  upon 
  rocks 
  of 
  the 
  older 
  systems. 
  Two 
  

   series 
  of 
  these 
  beds 
  have 
  been 
  differentiated. 
  The 
  ear- 
  

   lier 
  of 
  these 
  is 
  with 
  little 
  doubt 
  largely 
  Eocene. 
  The 
  

   later 
  series 
  presents 
  conflicting 
  paleontologic 
  evidence. 
  

   The 
  available 
  fossils 
  are 
  few 
  and 
  poorly 
  preserved, 
  

   chiefly 
  gastropods. 
  Some 
  of 
  them 
  suggest 
  Eocene 
  age 
  

   and 
  others 
  Pliocene. 
  Possibly 
  Cligocene 
  beds 
  may 
  be 
  

   included 
  in 
  one 
  of 
  the 
  divisions. 
  The 
  later 
  series 
  of 
  beds 
  

   has 
  long 
  been 
  tentatively 
  considered 
  Pliocene 
  and 
  it 
  ap- 
  

   pears 
  unwise 
  to 
  change 
  this 
  reference 
  until 
  more 
  satis- 
  

   factory 
  evidence 
  is 
  available. 
  The 
  correlation 
  of 
  the 
  

   various 
  Tertiary 
  patches 
  thus 
  rests 
  mainly 
  upon 
  lith- 
  

   ologic 
  and 
  structural 
  data. 
  The 
  distinction 
  between 
  

   Eocene 
  and 
  Pliocene 
  (?) 
  in 
  this 
  region 
  is 
  locally 
  difficult 
  

   where 
  limestones 
  of 
  the 
  two 
  groups 
  are 
  in 
  contact 
  or 
  

   proximity. 
  Thus 
  certain 
  beds 
  now 
  referred 
  to 
  the 
  Plio- 
  

   cene 
  (!) 
  may 
  prove 
  to 
  be 
  Eocene. 
  The 
  combined 
  thick- 
  

   ness 
  of 
  the 
  two 
  Tertiary 
  formations 
  is 
  probably 
  more 
  

  

  than 
  2,500 
  feet. 
  

  

  Eocene 
  series. 
  

  

  The 
  beds 
  assigned 
  to 
  the 
  Eocene 
  series 
  consist 
  of 
  con- 
  

   glomerates, 
  soft 
  sandstones, 
  and 
  fresh 
  water 
  limestones. 
  

   They 
  are 
  referred 
  to 
  the 
  Wasatch 
  formation. 
  The 
  un- 
  

   conformity 
  at 
  their 
  base 
  is 
  very 
  pronounced. 
  

  

  1 
  Published 
  by 
  permission 
  of 
  the 
  Director 
  of 
  the 
  U. 
  S. 
  Geological 
  Survey. 
  

  

  