﻿86 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  In 
  Gilbert's 
  section 
  the 
  whole 
  Cretaceous 
  section 
  is 
  not 
  given. 
  He 
  

   says 
  the 
  lowest 
  Cretaceous 
  bed 
  is 
  No. 
  8 
  or 
  No. 
  10, 
  

  

  In 
  a 
  previous 
  page 
  I 
  have 
  compared 
  my 
  sections 
  with 
  that 
  of 
  Dr. 
  

   Newberry, 
  and 
  the 
  table 
  just 
  given 
  will 
  show 
  how 
  closely 
  all 
  the 
  sec- 
  

   tions 
  of 
  the 
  Trias 
  agree. 
  

  

  JURASSIC. 
  

  

  Immediately 
  above 
  the 
  red 
  beds 
  is 
  a 
  group 
  of 
  shales 
  and 
  marls, 
  with 
  

   thin 
  bands 
  of 
  limestone 
  near 
  the 
  base. 
  These 
  beds 
  are 
  variegated 
  in 
  

   color, 
  and 
  correspond, 
  lithologically 
  and 
  stratigraphically, 
  with 
  the 
  

   beds 
  that, 
  in 
  Eastern 
  and 
  Central 
  Colorado, 
  I 
  referred 
  to 
  the 
  Jura. 
  I 
  

   was 
  unable 
  to 
  make 
  any 
  detailed 
  sections, 
  but, 
  as 
  far 
  as 
  seen, 
  they 
  ap- 
  

   peared 
  to 
  correspond 
  closely 
  with 
  the 
  beds 
  measured 
  in 
  the 
  sections 
  on 
  

   the 
  Gunnison 
  in 
  1874.* 
  In 
  that 
  locality 
  the 
  series 
  consisted 
  of 
  soft 
  ar- 
  

   gillaceous 
  and 
  arenaceous 
  shales, 
  often 
  gypsiferous 
  and 
  variegated 
  in 
  

   color, 
  with 
  bands 
  of 
  yellow 
  siliceous 
  sandstone 
  and 
  gray 
  and 
  bluish 
  - 
  

   gray 
  limestones 
  in 
  thin 
  beds. 
  The 
  total 
  thickness 
  was 
  nearly 
  250 
  feet. 
  

   In 
  the 
  district 
  under 
  consideration, 
  the 
  thickness 
  is 
  probably 
  greater 
  

   than 
  that 
  on 
  the 
  Gunnison. 
  The 
  areas 
  in 
  which 
  this 
  series 
  is 
  exposed 
  

   are 
  comparatively 
  small. 
  In 
  the 
  " 
  Great 
  Uncompahgre 
  Plateau 
  " 
  there 
  

   are 
  several 
  areas 
  where 
  these 
  variegated 
  beds 
  are 
  the 
  surface 
  formation. 
  

   These 
  will 
  be 
  readily 
  understood 
  by 
  glancing 
  at 
  the 
  map. 
  In 
  the 
  mono- 
  

   clinal 
  fold 
  toward 
  the 
  southwest, 
  the 
  creeks 
  that 
  cut 
  across 
  it 
  expose 
  

   the 
  Jurassic 
  beneath 
  the 
  Dakota 
  group. 
  The 
  Jurassic 
  is 
  also 
  seen 
  in 
  the 
  

   bottoms 
  of 
  the 
  canons 
  draining 
  the 
  plateau 
  bordering 
  the 
  San 
  Miguel 
  on 
  

   the 
  west. 
  As 
  we 
  go 
  northwest, 
  the 
  Dakota 
  sandstones 
  are 
  absent, 
  hav- 
  

   ing 
  been 
  eroded 
  away 
  j 
  and 
  still 
  farther 
  along, 
  the 
  Jurassic 
  shales 
  are 
  

   also 
  absent. 
  

  

  In 
  the 
  region 
  about 
  the 
  Sierra 
  la 
  Sal, 
  there 
  is 
  also 
  a 
  limited 
  area 
  of 
  

   Jurassic 
  dipping 
  from 
  the 
  mountains. 
  

  

  In 
  a 
  preceding 
  portion 
  of 
  this 
  chapter 
  I 
  have 
  spoken 
  of 
  the 
  conflict- 
  

   ing 
  evidence 
  in 
  regard 
  to 
  the 
  Trias, 
  and 
  showed 
  that 
  Jurassic 
  '? 
  fossils 
  

   have 
  been 
  found 
  at 
  the 
  base 
  of 
  the 
  Trias. 
  The 
  sections 
  given 
  on 
  page 
  

   85 
  will 
  show 
  the 
  relations 
  of 
  the 
  Jurassic 
  strata 
  to 
  those 
  of 
  the 
  Trias. 
  

   In 
  Mr. 
  Gilbert's 
  section 
  I 
  am 
  inclined 
  to 
  think 
  that 
  a 
  portion 
  of 
  the 
  

   beds 
  referred 
  by 
  him 
  to 
  the 
  Cretaceous 
  are 
  Jurassic. 
  

  

  • 
  Report 
  United 
  States 
  Geological 
  Survey, 
  1874, 
  pp. 
  126, 
  127. 
  

  

  