﻿Stratigraphy 
  of 
  Eastern 
  New 
  Mexico. 
  11& 
  

  

  Seco 
  with 
  the 
  Eio 
  Chama, 
  in 
  Rio 
  Arriba 
  County, 
  on 
  the 
  

   road 
  between 
  Abiquiu 
  and 
  Tierra 
  Amarilla. 
  A 
  gener- 
  

   alized 
  section 
  of 
  the 
  Trias 
  at 
  this 
  locality, 
  beginning 
  with 
  

   the 
  base, 
  follows 
  : 
  

  

  1. 
  Shinarump 
  sandstone 
  and 
  conglomerate, 
  prob- 
  

  

  ably 
  the 
  equivalent 
  of 
  the 
  Glorieta 
  sandstone 
  

   farther 
  east 
  and 
  southeast. 
  Color 
  varies 
  from 
  

   purple 
  to 
  light 
  buff 
  but 
  is 
  generally 
  brown, 
  

   often 
  stained 
  on 
  the 
  surface 
  with 
  black 
  oxide. 
  

   Sandstone 
  cross-bedded. 
  Lower 
  portion 
  con- 
  

   glomeratic, 
  with 
  well 
  rounded 
  pebbles 
  and 
  

   bowlders 
  of 
  crystallines. 
  Rests 
  unconform- 
  

   ably 
  on 
  Permian 
  red 
  sandy 
  clays 
  ± 
  150' 
  

  

  2. 
  Sandy 
  clays, 
  dark 
  maroon, 
  streaked 
  and 
  mottled 
  

  

  with 
  light 
  gray, 
  blue 
  and 
  green. 
  At 
  least 
  200' 
  

  

  3. 
  Sandstone, 
  massive, 
  friable, 
  fine-grained, 
  with 
  

  

  curved 
  joints, 
  weathering 
  by 
  exfoliation 
  into 
  

   alcoves. 
  Much 
  cross-bedded 
  locally, 
  and 
  in 
  all 
  

   probability 
  at 
  least 
  partly 
  of 
  eolian 
  origin. 
  

   Color 
  in 
  lower 
  half 
  varies 
  from 
  buffi 
  to 
  brick- 
  

   red, 
  becomes 
  buff 
  above, 
  and 
  is 
  light 
  yellow 
  in 
  

   upper 
  50' 
  ± 
  200' 
  

  

  4. 
  Alabaster 
  gypsum, 
  resting 
  on 
  irregular 
  surface 
  

  

  of 
  (3) 
  . 
  Erosion 
  channels 
  in 
  the 
  gypsum 
  filled 
  

   with 
  buff 
  sandstone. 
  Maximum 
  thickness 
  .... 
  ± 
  50' 
  

   Unconformity. 
  

  

  5. 
  Sands 
  and 
  sandy 
  clays, 
  pink, 
  purple, 
  buff 
  and 
  

  

  drab 
  in 
  color 
  ± 
  350' 
  

  

  6. 
  Sandstone, 
  buff 
  ± 
  200' 
  

  

  7. 
  Clays, 
  whitish 
  40- 
  ± 
  50' 
  

  

  8. 
  Clays, 
  drab, 
  weathering 
  in 
  badlands. 
  At 
  least 
  200' 
  

  

  The 
  total 
  thickness 
  of 
  strata 
  between 
  the 
  top 
  of 
  (1) 
  

   and 
  the 
  top 
  of 
  (6) 
  is 
  about 
  1600 
  feet, 
  hence 
  the 
  estimates 
  

   of 
  thicknesses 
  given 
  above 
  are 
  too 
  small. 
  The 
  location 
  

   of 
  this 
  section 
  is 
  on 
  the 
  west 
  flank 
  of 
  the 
  anticline 
  mark- 
  

   ing^ 
  the 
  southeastern 
  end 
  of 
  the 
  San 
  Juan 
  Mountains 
  

   uplift. 
  Along 
  this 
  anticline, 
  north 
  of 
  Abiquiu, 
  several 
  

   hundred 
  feet 
  of 
  Permian 
  red 
  beds 
  are 
  exposed. 
  The 
  age 
  

   of 
  beds 
  (5) 
  to 
  (8) 
  is 
  unknown, 
  but 
  beds 
  (1) 
  to 
  (4) 
  inclu- 
  

   sive 
  are 
  Upper 
  Trias. 
  The 
  above 
  sedimentary 
  rocks 
  are 
  

   concealed 
  to 
  the 
  south 
  and 
  east 
  by 
  great 
  thicknesses 
  of 
  

   volcanic 
  pyroclastics 
  and 
  flows 
  (rhyolite, 
  andesite 
  and 
  

   basalt 
  in 
  upward 
  succession). 
  These 
  volcanic 
  rocks 
  fill 
  

   the 
  basin 
  of 
  the 
  upper 
  Rio 
  Grande 
  in 
  New 
  Mexico 
  and 
  

   form 
  the 
  extensive 
  mesa 
  surfaces 
  of 
  the 
  San 
  Pedro, 
  Val- 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series 
  Vol. 
  XLIX, 
  No. 
  290.— 
  February, 
  1920. 
  

   9 
  

  

  