﻿246 
  EEPORT 
  UJJITED 
  STATEH 
  GEOLOGICAL 
  SURVEY. 
  

  

  to 
  this 
  fold 
  while 
  on 
  Station 
  1, 
  from 
  which 
  point 
  it 
  appears 
  to 
  flex 
  out- 
  

   ward 
  toward 
  the 
  south, 
  as 
  plainly 
  indicated 
  by 
  a 
  line 
  of 
  hogbacks. 
  It 
  

   is 
  these 
  hogbacks 
  that 
  form 
  the 
  southern 
  rim 
  of 
  the 
  basin 
  just 
  described. 
  

   By 
  reference 
  to 
  the 
  map 
  it 
  will 
  be 
  seen 
  that 
  this 
  outcropping 
  line 
  of 
  

   harder 
  beds 
  has 
  turned 
  the 
  river 
  considerably 
  to 
  the 
  westward, 
  and 
  that 
  

   a 
  number 
  of 
  long 
  washes 
  run 
  parallel 
  with 
  the 
  strike 
  of 
  the 
  strata. 
  

  

  Station 
  VI 
  was 
  made 
  on 
  the 
  highest 
  point 
  of 
  a 
  small 
  group 
  of 
  hills 
  

   that 
  lies 
  on 
  the 
  line 
  of 
  the 
  fold 
  about 
  8 
  miles 
  east 
  of 
  its 
  intersection 
  with 
  

   the 
  river 
  and 
  some 
  15 
  miles 
  southwest 
  of 
  Station 
  1. 
  The 
  hills 
  are 
  

   capped 
  by 
  a 
  massive 
  white 
  sandstone, 
  25 
  or 
  30 
  feet 
  thick. 
  On 
  the 
  sum- 
  

   mit 
  of 
  the 
  hill 
  on 
  which 
  our 
  station 
  was 
  made 
  we 
  observed 
  large 
  heaps 
  

   of 
  cinders. 
  I 
  am 
  led 
  to 
  attribute 
  their 
  presence 
  to 
  the 
  burning 
  of 
  coal- 
  

   beds 
  which 
  at 
  one 
  time 
  probably 
  occurred 
  on 
  the 
  upper 
  surface 
  of 
  the 
  

   sandstones. 
  In 
  numerous 
  localities, 
  both 
  east 
  and 
  west, 
  I 
  have 
  en- 
  

   countered 
  portions 
  of 
  strata 
  that 
  had 
  the 
  appearance 
  of 
  having 
  been 
  

   burned 
  as 
  in 
  a 
  kiln, 
  and 
  I 
  have 
  noticed 
  that 
  in 
  every 
  case 
  the 
  phenome- 
  

   non 
  occurs 
  in 
  coal-bearing 
  strata, 
  and 
  also 
  that 
  coal 
  is 
  locally 
  absent 
  

   in 
  all 
  such 
  places. 
  Dr. 
  Newberry 
  observed 
  a 
  similar 
  condition 
  of 
  coal 
  

   strata 
  in 
  Arizona, 
  and 
  Dr. 
  Peale 
  and 
  others 
  in 
  Colorado. 
  Beneath 
  the 
  

   sandstones 
  in 
  the 
  bluff 
  faces 
  a 
  considerable 
  thickness 
  of 
  soft 
  clay 
  and 
  

   sandy 
  shales 
  is 
  exposed. 
  These 
  are 
  probably 
  some 
  hundreds 
  of 
  feet 
  

   in 
  thickness, 
  and 
  seem 
  to 
  rest 
  upon 
  a 
  group 
  of 
  yellowish 
  sandstones 
  

   which 
  outcrop 
  in 
  the 
  river 
  bluff 
  a 
  few 
  miles 
  to 
  the 
  west, 
  and 
  from 
  which 
  

   I 
  obtained 
  a 
  few 
  imperfect 
  fossils, 
  which 
  resemble 
  those 
  of 
  No. 
  5 
  Creta- 
  

   ceous 
  in 
  the 
  region 
  about 
  Greeley. 
  If 
  these 
  are 
  really 
  Upper 
  Cretaceous 
  

   fossils, 
  the 
  probabilities 
  are 
  that 
  the 
  coal-bearing 
  horizon 
  of 
  Station 
  5 
  

   corresponds 
  with 
  the 
  so-called 
  Lignitic 
  horizon 
  of 
  the 
  Eastern 
  Colorado 
  

   region. 
  The 
  greater 
  part 
  of 
  the 
  formations 
  in 
  this 
  part 
  of 
  the 
  valley 
  are 
  

   obscured 
  by 
  terrace 
  deposit, 
  and 
  the 
  absolute 
  identification 
  of 
  the 
  

   isolated 
  outcrops 
  cannot 
  easily 
  be 
  made. 
  Near 
  Station 
  6 
  the 
  river 
  cuts 
  

   across 
  the 
  gently 
  tipped 
  strata 
  of 
  Upper 
  Coal 
  Group 
  (3, 
  general 
  section), 
  

   exposing 
  a 
  very 
  good 
  section. 
  In 
  descending 
  the 
  river 
  we 
  observe 
  in 
  the 
  

   bluff' 
  a 
  whitish 
  massive 
  sandstone, 
  the 
  same 
  as 
  that 
  of 
  Station 
  V, 
  which 
  

   has 
  a 
  thickness 
  of 
  nearly 
  100 
  feet 
  ; 
  following 
  this 
  are 
  about 
  150 
  feet 
  of 
  

   brownish 
  sandstones, 
  with 
  interbedded 
  shale 
  and 
  marl 
  which 
  seem 
  to 
  

   have 
  been 
  reddened 
  by 
  heat. 
  A 
  little 
  farther 
  on, 
  where 
  a 
  deep 
  side 
  

   gulch 
  has 
  notched 
  the 
  bluff, 
  a 
  coal-seam 
  upwards 
  of 
  13 
  feet 
  in 
  thickness 
  

   is 
  exposed. 
  The 
  quality 
  of 
  this 
  coal 
  is 
  by 
  no 
  means 
  good, 
  and 
  seams 
  of 
  

   clay 
  and 
  shale 
  are 
  so 
  numerous 
  as 
  to 
  make 
  up 
  nearly 
  half 
  of 
  the 
  thick- 
  

   ness. 
  On 
  the 
  opposite 
  side 
  of 
  the 
  stream 
  a 
  similar 
  outcrop 
  occurs. 
  

   Above 
  the 
  coal, 
  that 
  is 
  to 
  the 
  south 
  of 
  the 
  coal 
  outcrop, 
  is 
  a 
  series 
  of 
  

   brown 
  sandstones 
  several 
  hundred 
  fe;jt 
  in 
  thickness, 
  in 
  which 
  are 
  seams 
  

   of 
  lignite 
  and 
  dark 
  carbonaceous 
  shale, 
  also 
  gray 
  and 
  purplish 
  shales. 
  

   These 
  all 
  belong 
  to 
  the 
  Upper 
  Coal 
  Group 
  (group 
  3 
  of 
  the 
  general 
  sec- 
  

   tion) 
  and 
  have 
  a 
  very 
  marked 
  general 
  resemblance 
  to 
  the 
  Lignitic 
  Coal- 
  

   Measures 
  of 
  Golden 
  City 
  and 
  the 
  Boulder 
  Valley. 
  The 
  white 
  sandstone 
  

   at 
  the 
  base 
  is 
  probably 
  identical 
  with 
  the 
  Pictured 
  Cliffs 
  Group 
  (4 
  of 
  the 
  

   general 
  section). 
  The 
  dip 
  of 
  the 
  sandstones 
  of 
  the 
  Coal 
  Group 
  varies 
  

   from 
  4° 
  to 
  UP, 
  and 
  the 
  strike 
  at 
  the 
  river 
  is 
  nearly 
  northeast 
  and 
  south- 
  

   west. 
  The 
  San 
  Juan 
  fold 
  crosses. 
  the 
  river 
  with 
  these 
  strata, 
  and 
  is 
  the 
  

   cause 
  of 
  the 
  increased 
  dip. 
  The 
  coal 
  strata 
  are 
  succeeded 
  by 
  a 
  heavy 
  

   thickness 
  of 
  sand 
  and 
  clay 
  shales 
  and 
  marls 
  (the 
  Bad 
  Land 
  Group 
  of 
  the 
  

   general 
  section), 
  over 
  which 
  the 
  river 
  runs 
  to 
  its 
  junction 
  with 
  the 
  San 
  

   Juan. 
  Since 
  leaving 
  the 
  base 
  of 
  the 
  mountains 
  the 
  river 
  has 
  gradually 
  

   changed 
  from 
  a 
  sparkling 
  mountain 
  torrent 
  to 
  a 
  slothful, 
  slimy 
  stream, 
  

  

  