﻿250 
  EEipOET 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  • 
  

  

  in 
  a 
  few 
  cases 
  small 
  pebbles 
  of 
  Carboniferous 
  limestone 
  containing 
  Coal- 
  

   Measure 
  fossils 
  were 
  found. 
  

  

  At 
  the 
  mouth 
  of 
  the 
  La 
  Plata 
  the 
  river 
  h^s 
  encroached 
  upon 
  a 
  subor- 
  

   dinate 
  terrace, 
  and 
  a 
  sharp 
  bluff 
  is 
  formed 
  in 
  which 
  there 
  is 
  exposed 
  a 
  

   stratum 
  of 
  compact 
  massive 
  sandstone. 
  This 
  stratum 
  seems 
  to 
  occur 
  in 
  

   the 
  lower 
  part 
  of 
  the 
  Bad 
  Land 
  Group, 
  and 
  can 
  be 
  traced 
  by 
  a 
  pretty 
  con- 
  

   tinuous 
  line 
  of 
  outcrop 
  all 
  along 
  the 
  slope 
  south 
  and 
  southwest 
  of 
  the 
  

   PinonMesa: 
  beneathit 
  are 
  the 
  Coal 
  Group 
  outcrops, 
  which 
  show 
  a 
  predom- 
  

   inance 
  of 
  soft, 
  yellow 
  sandstones 
  interbedded 
  with 
  clay 
  and 
  sand 
  shales. 
  

   These 
  beds 
  occupy 
  the 
  valley 
  from 
  the 
  mouth 
  of 
  the 
  Kio 
  La 
  Plata 
  to 
  the 
  

   outcrop 
  of 
  the 
  white 
  sandstones 
  of 
  the 
  Pictured 
  Cliffs, 
  15 
  miles 
  below. 
  

   The 
  dip 
  is 
  to 
  the 
  east, 
  at 
  a 
  very 
  slight 
  angle. 
  Before 
  reaching 
  the 
  Pic- 
  

   tured 
  Cliffs, 
  in 
  descending 
  the 
  river, 
  a 
  large 
  remnant 
  of 
  one 
  of 
  the 
  lower 
  

   terraces 
  appears 
  on 
  the 
  right, 
  a 
  considerable 
  space 
  above 
  and 
  to 
  the 
  

   right 
  being 
  reduced 
  to 
  the 
  flood-plain 
  of 
  the 
  river. 
  All 
  along 
  the 
  south 
  

   face 
  of 
  this 
  remnant 
  are 
  outcrops 
  of 
  the 
  Coal-Measures, 
  and 
  near 
  their 
  

   base 
  a 
  coal-seam, 
  26 
  feet 
  in 
  thickness, 
  of 
  light 
  brown 
  lignite, 
  is 
  exposed. 
  

   Beneath 
  this 
  a 
  sharp 
  bluff 
  of 
  massive 
  grayish-white 
  sandstone 
  rises 
  from 
  

   the 
  water-level, 
  and 
  after 
  following 
  the 
  river 
  for 
  a 
  short 
  distance 
  circles 
  

   around 
  to 
  the 
  west 
  and 
  north. 
  The 
  trail 
  passes 
  up 
  over 
  the 
  low 
  promon- 
  

   tory 
  formed 
  of 
  this 
  sandstone, 
  descends 
  again 
  to 
  the 
  river-bottom, 
  and 
  

   follows 
  for 
  a 
  while 
  the 
  base 
  of 
  the 
  bluff. 
  The 
  sandstone 
  stratum 
  is 
  qnite 
  

   massive, 
  and 
  breaks 
  down 
  in 
  great 
  smooth-faced 
  blocks. 
  On 
  these 
  

   thousands 
  of 
  fantastic 
  figures 
  have 
  been 
  engraved, 
  recording, 
  perhaps, 
  

   the 
  history 
  of 
  some 
  former 
  occupants 
  of 
  the 
  valley. 
  Beneath 
  the 
  mas- 
  

   sive 
  stratum 
  are 
  several 
  layers 
  of 
  brownish 
  sandstone. 
  To 
  the 
  group 
  I 
  

   gave 
  the 
  name 
  suggested 
  by 
  the 
  picture-writing. 
  On 
  the 
  upper 
  surface 
  

   of 
  the 
  Pictured 
  Cliff" 
  sandstone, 
  and 
  not 
  more 
  than 
  30 
  feet 
  below 
  the 
  

   great 
  bed 
  of 
  lignite, 
  I 
  discovered 
  a 
  heavy 
  bed 
  of 
  fossil-shells, 
  in 
  which 
  

   were 
  a 
  number 
  of 
  forms 
  having 
  Upper 
  Cretaceous 
  fasces. 
  They 
  were 
  

   quite 
  similar 
  to 
  the 
  forms 
  found 
  beneath 
  the 
  coal 
  on 
  the 
  Cache 
  la 
  

   Poudre 
  and 
  Platte 
  Elvers. 
  One 
  specimen 
  of 
  Corhula 
  was 
  all 
  that 
  could 
  

   be 
  preserved, 
  as 
  they 
  were 
  extremely 
  fragile. 
  From 
  the 
  first 
  I 
  have 
  

   been 
  very 
  much 
  inclined 
  to 
  consider 
  this 
  horizon 
  the 
  top 
  of 
  the 
  Creta- 
  

   ceous, 
  and 
  I 
  am 
  well 
  convinced, 
  after 
  carefully 
  comparing 
  my 
  sections 
  

   with 
  those 
  made 
  by 
  Doctors 
  White 
  and 
  Peale 
  in 
  Northwestern 
  Colorado, 
  

   that 
  my 
  Upper 
  Coal 
  Group 
  occupies 
  a 
  place 
  in 
  the 
  section 
  correspond- 
  

   ing 
  to 
  that 
  of 
  the 
  Laramie 
  Group 
  in 
  theirs. 
  

  

  "in 
  New 
  Mexico 
  Professor 
  Cope 
  observed 
  a 
  similar 
  group 
  of 
  sandstones 
  

   occupying 
  the 
  same 
  relative 
  place 
  in 
  the 
  section, 
  but 
  did 
  not 
  attempt 
  to 
  

   place 
  it 
  either 
  with 
  the 
  Cretaceous 
  rocks 
  which 
  lay 
  beneath, 
  or 
  with 
  

   the 
  well-identified 
  Tertiary 
  strata 
  which 
  came 
  above. 
  Prof. 
  C. 
  A. 
  White 
  

   has 
  recently 
  made 
  the 
  suggestion 
  that 
  this 
  group 
  of 
  rocks 
  be 
  classed 
  

   as 
  Post-Cretaceous 
  until 
  sufficient 
  proof 
  can 
  be 
  gathered 
  to 
  decide 
  the 
  

   question 
  of 
  age. 
  

  

  Beneath 
  the 
  massive 
  sandstones 
  of 
  the 
  Pictured 
  Cliff's, 
  and 
  about 
  lOU 
  

   feet 
  below 
  the 
  first 
  fossil 
  horizon, 
  I 
  obtained 
  from 
  a 
  bard 
  fine-grained 
  

   chocolate-brown 
  sandstone 
  a 
  number 
  of 
  poorly 
  preserved 
  fossils. 
  They 
  

   included 
  Tellina 
  scitula, 
  ScapUtes 
  Warrenii, 
  and 
  unidentified 
  species 
  of 
  

   Cardium 
  and 
  Actceon. 
  

  

  West 
  of 
  the 
  Pictured 
  Cliffs 
  the 
  river 
  runs 
  through 
  a 
  broad 
  valley 
  that 
  

   opens 
  out 
  to 
  the 
  north 
  and 
  south 
  ; 
  beyond 
  this 
  an 
  immense 
  hogback 
  

   ridge 
  composed 
  of 
  Upper 
  Cretaceous 
  sandstones 
  crosses 
  the 
  valley 
  at 
  

   right 
  angles 
  to 
  the 
  river's 
  course. 
  The 
  space 
  between 
  the 
  Pictured 
  

   Cliffs 
  and 
  the 
  Great 
  Hogback 
  or 
  ' 
  ' 
  Creston," 
  as 
  it 
  is 
  called 
  by 
  Dr. 
  Newberry, 
  

   is 
  occupied 
  by 
  a 
  group 
  of 
  sands 
  and 
  clays, 
  group 
  5 
  of 
  the 
  general 
  sec- 
  

  

  