﻿210 
  EEPOKT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  and 
  long-continued 
  action 
  of 
  water, 
  the 
  drift 
  there 
  has 
  not 
  preserved 
  

   the 
  characteristic 
  red 
  color 
  that 
  may 
  elsewhere 
  be 
  observed 
  in 
  still 
  

   more 
  recent 
  deposits. 
  The 
  clay, 
  which 
  contains 
  the 
  coloring-matter, 
  

   has 
  been 
  gradually 
  washed 
  away, 
  or 
  has 
  been 
  so 
  distributed 
  that 
  it 
  

   can 
  no 
  longer 
  have 
  any 
  effect 
  upon 
  the 
  general 
  coloring 
  of 
  the 
  drift, 
  

   which 
  now 
  appears 
  as 
  greyish-brown. 
  

  

  It 
  is 
  possible, 
  upon 
  cursory 
  examination 
  only, 
  to 
  mistake 
  these 
  red 
  

   Carboniferous 
  beds 
  for 
  the 
  "red 
  beds" 
  of 
  Mesozoic 
  age. 
  As 
  character- 
  

   istics, 
  however, 
  it 
  may 
  be 
  mentioned, 
  that 
  the 
  latter 
  show 
  greater 
  inten- 
  

   sity 
  of 
  coloring, 
  greater 
  tendency 
  to 
  weather 
  in 
  steep 
  bluffs, 
  and 
  more 
  

   interstrata 
  of 
  reddish-white 
  or 
  pure 
  white 
  sandstones. 
  Furthermore, 
  

   they 
  are 
  comparatively 
  rarely 
  met 
  with 
  within 
  the 
  limits 
  of 
  the 
  high 
  

   mountains, 
  occurring 
  mainly 
  along 
  their 
  borders. 
  An 
  examination 
  as 
  

   to 
  lithological 
  features 
  will 
  disclose 
  the 
  fact, 
  that 
  generally 
  the 
  Meso- 
  

   zoic 
  beds 
  show 
  a 
  more 
  abundant 
  supply 
  of 
  clay 
  in 
  the 
  sandstones, 
  as 
  

   well 
  as 
  more 
  interstrata 
  of 
  bright 
  red 
  shales 
  and 
  shaly 
  marls. 
  

  

  Jura-Trias. 
  — 
  This 
  group 
  is 
  represented 
  at 
  but 
  one 
  locality 
  in 
  our 
  dis- 
  

   trict. 
  Extending 
  southward 
  along 
  the 
  Front 
  Eange, 
  it 
  curves 
  around 
  

   the 
  southern 
  end 
  of 
  the 
  Greenhorn 
  Mountains. 
  A 
  short 
  distance 
  west 
  

   of 
  the 
  main 
  peak 
  of 
  that 
  spur 
  the 
  characteristic 
  "red 
  beds" 
  no 
  longer 
  

   appear. 
  It 
  differs 
  in 
  nothing 
  here 
  from 
  the 
  analogous 
  occurrences 
  far- 
  

   ther 
  north. 
  

  

  Cretaceous. 
  — 
  Three 
  groups 
  represent 
  the 
  Cretaceous 
  formation 
  in 
  our 
  

   district 
  — 
  the 
  Dakota, 
  Colorado, 
  and 
  Fox 
  Hills. 
  Owing 
  to 
  considerable 
  

   changes, 
  both 
  in 
  vertical 
  dimensions 
  and 
  in 
  the 
  lithological 
  character 
  of 
  

   the 
  strata, 
  as 
  well 
  as 
  in 
  the 
  fossils, 
  it 
  was 
  imijossible 
  to 
  apply 
  the 
  former 
  

   division 
  into 
  five 
  groups. 
  It 
  is 
  but 
  natural 
  that, 
  where 
  large 
  areas 
  in- 
  

   tervene, 
  as 
  in 
  this 
  instance, 
  very 
  decided 
  changes 
  should 
  take 
  place, 
  

   altering 
  the 
  general 
  arrangement 
  and 
  detail-features 
  in 
  such 
  a 
  manner 
  

   that 
  the 
  former 
  scale 
  is 
  no 
  longer 
  applicable. 
  By 
  classifying 
  the 
  forma- 
  

   tion, 
  as 
  above 
  stated, 
  we 
  have 
  been 
  able 
  to 
  carry 
  out 
  successfully 
  a 
  di- 
  

   vision 
  that 
  is 
  perfectly 
  natural 
  for 
  that 
  region, 
  and 
  have 
  had 
  no 
  diffi- 
  

   culty 
  in 
  recognizing 
  the 
  horizons 
  established. 
  

  

  Along 
  the 
  eastern 
  base 
  of 
  the 
  Lower 
  Sangre 
  de 
  Cristo 
  Eange 
  the 
  typ- 
  

   ical 
  upturning 
  of 
  Cretaceous 
  beds 
  against 
  the 
  slope 
  of 
  the 
  mountains 
  

   could 
  again 
  be 
  observed. 
  In 
  this 
  case 
  it 
  was 
  rather 
  extreme, 
  inasmuch 
  

   as 
  the 
  older 
  Carboniferous 
  strata 
  several 
  times 
  were 
  noticed 
  to 
  rest 
  upon 
  

   the 
  I)akota 
  sandstones. 
  No 
  trace 
  of 
  the 
  Jura-Trias 
  was 
  seen 
  to 
  occur 
  

   between 
  the 
  Carboniferous 
  and 
  the 
  Cretaceous, 
  as 
  is 
  the 
  case 
  along 
  the 
  

   foot 
  of 
  the 
  Front 
  Eange. 
  There 
  seems 
  to 
  me 
  no 
  doubt 
  that 
  the 
  up- 
  

   turning 
  of 
  the 
  Cretaceous 
  edges 
  is 
  due 
  to 
  the 
  rise 
  of 
  the 
  main 
  Eocky 
  

   Mountains 
  at 
  some 
  time 
  during 
  the 
  Tertiary 
  period. 
  This 
  view 
  has 
  been 
  

   very 
  ably 
  presented 
  and 
  sustained 
  by 
  Dr. 
  Peale.* 
  It 
  is 
  the 
  only 
  way 
  in 
  

   which 
  to 
  account 
  for 
  the 
  uniformity 
  of 
  the 
  upturn 
  observed 
  for 
  a 
  dis- 
  

   tance 
  of 
  many 
  miles. 
  As 
  I 
  have 
  expressed 
  myself 
  in 
  the 
  report 
  of 
  1873, 
  

   I 
  hold 
  that 
  the 
  elevation 
  took 
  place 
  along 
  certain 
  lines 
  to 
  a 
  greater 
  ex- 
  

   tent 
  than 
  in 
  the 
  entire 
  mass 
  of 
  mountains, 
  and 
  we 
  can 
  thereby 
  explain 
  

   an 
  apparent 
  contradiction, 
  when 
  we 
  do 
  not 
  find 
  the 
  corresponding 
  effect 
  

   on 
  both 
  sides 
  of 
  a 
  range. 
  No 
  Cretaceous 
  waters 
  penetrated 
  westward 
  

   through 
  any 
  opening 
  in 
  the 
  Sangre 
  de 
  Cristo 
  Eange. 
  With 
  the 
  excep- 
  

   tion 
  of 
  small 
  local 
  deposits 
  belonging 
  to 
  the 
  Miocene, 
  we 
  find 
  no 
  sedi- 
  

   mentary 
  beds 
  younger 
  than 
  the 
  Carboniferous 
  until 
  we 
  arrive 
  at 
  the 
  

   western 
  slope 
  of 
  the 
  Sawatch 
  Eange. 
  From 
  there 
  southward 
  the 
  young- 
  

   est 
  Mesozoic 
  and 
  the 
  Cenozoic 
  formations 
  set 
  in. 
  It 
  is 
  here 
  more 
  par- 
  

  

  * 
  American 
  Journal 
  of 
  Science 
  and 
  Arts, 
  April, 
  1877, 
  p. 
  172. 
  

  

  