﻿EXDLicii.] 
  CONCLUSION 
  CARBONIFEROUS. 
  209 
  

  

  sume 
  for 
  tlie 
  group 
  exposed 
  at 
  station 
  94. 
  Between 
  the 
  two 
  outcrops 
  

   lies 
  an 
  intervening 
  distance 
  of 
  85 
  miles, 
  tbat 
  affords 
  no 
  clew 
  to 
  any 
  con- 
  

   nection, 
  either 
  in 
  former 
  periods 
  or 
  at 
  the 
  present 
  time, 
  below 
  the 
  sur- 
  

   face. 
  It 
  is 
  impossible, 
  therefore, 
  to 
  make 
  any 
  assertions 
  relative 
  to 
  an 
  

   identity 
  of 
  the 
  two 
  groups 
  as 
  regards 
  age, 
  but 
  I 
  incline 
  to 
  the 
  opinion 
  

   that 
  the 
  connection 
  formerly 
  existed, 
  mainly 
  following, 
  perhaps, 
  the 
  con- 
  

   tinental 
  divide, 
  and 
  that 
  the 
  present 
  high 
  altitude 
  of 
  the 
  volcanic 
  beds 
  

   in 
  the 
  Sawatch 
  Eange 
  is 
  due 
  to 
  such 
  connection. 
  In 
  speaking 
  of 
  the 
  

   volcanic 
  area 
  below, 
  a 
  synopsis 
  of 
  the 
  metamorphic 
  outcrops 
  occurring 
  

   within 
  its 
  limits 
  will 
  be 
  given, 
  with 
  a 
  view 
  to 
  presenting 
  the 
  former 
  

   hypsometric 
  conditions 
  as 
  far 
  as 
  possible. 
  

  

  Carhoniferous. 
  — 
  In 
  the 
  districts 
  of 
  1873 
  and 
  1874 
  the 
  Lower 
  Carbon- 
  

   iferous 
  strata 
  reached 
  a 
  good 
  development. 
  On 
  the 
  north 
  side 
  of 
  the 
  

   Arkansas 
  and 
  along 
  the 
  Animas 
  they 
  were 
  found 
  containing 
  character- 
  

   istic 
  fossils. 
  A 
  small 
  area 
  only 
  shows 
  an 
  exposure 
  of 
  the 
  same 
  in 
  our 
  

   present 
  section. 
  On 
  and 
  in 
  the 
  vicinity 
  of 
  Trinchera 
  Peak, 
  the 
  strata 
  

   are 
  found 
  that 
  belong 
  to 
  this 
  formation. 
  They 
  do 
  not 
  correspond 
  en- 
  

   tirely 
  with 
  those 
  observed 
  elsewhere, 
  evidently 
  having 
  besn 
  subjected 
  

   to 
  metamorphosing 
  influences. 
  In 
  geognostic 
  position 
  they 
  are 
  parallel 
  

   .to 
  the 
  lower 
  group 
  exposed 
  on 
  the 
  west 
  side 
  of 
  the 
  Animas,* 
  but 
  their 
  

   sandstones 
  are 
  changed 
  into 
  a 
  quartzitic 
  variety, 
  their 
  shales 
  into 
  

   argillites, 
  hard 
  and 
  brittle. 
  Above 
  them 
  a 
  blue 
  limestone 
  generally 
  

   occurs, 
  containing 
  fossils 
  that 
  denote 
  its 
  age.t 
  This 
  was 
  not 
  observed 
  

   in 
  the 
  range, 
  unless* 
  indeed, 
  the 
  limestones 
  found 
  in 
  Sangre 
  de 
  Cristo 
  

   and 
  Indian 
  Passes 
  should 
  represent 
  it. 
  They, 
  however, 
  show 
  beds 
  of 
  

   the 
  same 
  sandstone 
  on 
  either 
  side, 
  so 
  that 
  they 
  were 
  regarded 
  as 
  inter- 
  

   strata 
  rather 
  than 
  as 
  this 
  lower 
  group. 
  It 
  is 
  possible 
  that 
  the 
  contor- 
  

   tions 
  to 
  which 
  all 
  the 
  strata 
  were 
  subjected 
  at 
  those 
  localities 
  have 
  

   rendered 
  tbe 
  position 
  they 
  now 
  occupy 
  a 
  relatively 
  abnormal 
  one, 
  

   Reaching 
  a 
  very 
  considerable 
  thickness 
  and 
  playing 
  an 
  important 
  parr, 
  

   in 
  the 
  structure 
  of 
  the 
  Sangre 
  de 
  Cristo 
  Eange, 
  is 
  the 
  red 
  Carboniferous 
  

   sandstone. 
  It 
  generally 
  rests 
  upon 
  the 
  metamorphics, 
  having 
  assumed 
  

   a 
  similar 
  position 
  at 
  the 
  northern 
  end 
  of 
  the 
  range. 
  On 
  either 
  side 
  of 
  

   the 
  summit 
  it 
  dips 
  off 
  toward 
  the 
  valleys, 
  forming 
  only 
  at 
  oile 
  point, 
  

   station 
  21 
  of 
  1873, 
  the 
  summit 
  itself. 
  On 
  the 
  Arkansas 
  this 
  group 
  was 
  

   first 
  noticed, 
  and 
  from 
  its 
  geognostic 
  position 
  referred 
  to 
  the 
  Carbon- 
  

   iferous. 
  During 
  1875 
  the 
  ground 
  then 
  taken 
  was 
  vindicated 
  by 
  the 
  dis- 
  

   covery 
  of 
  undoubted 
  Carboniferous 
  fossils 
  in 
  interstrata 
  of 
  limestone 
  at 
  

   three 
  localities. 
  Besides 
  this. 
  Carboniferous 
  plants 
  were 
  found 
  in 
  the 
  

   sandstone 
  proper. 
  During 
  the 
  Cretaceous 
  period 
  the 
  beds 
  belonging 
  

   to 
  this 
  group 
  must 
  already 
  have 
  occupied 
  the 
  elevated 
  position 
  in 
  which 
  

   we 
  find 
  them 
  at 
  present, 
  thus 
  debarring 
  that 
  younger 
  formation 
  from 
  

   entering 
  the 
  western 
  country 
  beyond. 
  It 
  is 
  highly 
  probable 
  that 
  sub- 
  

   sequent 
  local 
  disturbances 
  have 
  produced 
  the 
  minor 
  plications 
  and 
  folds 
  

   we 
  observe, 
  but 
  the 
  general 
  position 
  of 
  the 
  sandstone 
  strata 
  was 
  deter- 
  

   mined 
  at 
  many 
  points 
  before 
  the 
  advent 
  of 
  tbe 
  later 
  Cretaceous 
  waters, 
  

   although 
  at 
  others 
  they 
  are 
  perfectly 
  conformable. 
  During 
  the 
  Carbon- 
  

   iferous 
  i)eriod 
  this 
  sandstone 
  must 
  have 
  formed 
  a 
  beach 
  for 
  a 
  very 
  long 
  

   time, 
  invaded 
  every 
  now 
  and 
  then 
  by 
  the 
  waters 
  that 
  deposited 
  the 
  

   limestones. 
  It 
  is 
  owing 
  to 
  this 
  temporary 
  invasion 
  that 
  we 
  find 
  them 
  

   to 
  be 
  of 
  local 
  occurrence 
  only, 
  and 
  not 
  forming 
  constant 
  geognostic 
  

   horizons. 
  As 
  the 
  latest 
  action 
  these 
  sandstones 
  have 
  taken 
  in 
  the 
  geo- 
  

   logical 
  history 
  of 
  tbe 
  region, 
  we 
  may 
  regard 
  tbe 
  furnishing 
  of 
  drift 
  in 
  

   San 
  Luis 
  Valley. 
  Consequent 
  upon 
  being 
  subjected 
  to 
  the 
  repeated 
  

  

  " 
  United 
  States 
  Geological 
  Report 
  1874, 
  p. 
  214. 
  

  

  t 
  United 
  States 
  Geological 
  Report 
  1873, 
  p. 
  311 
  ; 
  Report 
  1874, 
  p. 
  216. 
  

  

  14 
  G 
  S 
  

  

  