﻿EXDLicn] 
  SANGRE 
  DE 
  CRISTO 
  — 
  CARBONIFEROUS. 
  113 
  

  

  This 
  trachyte 
  covers 
  to 
  a 
  great 
  extent 
  the 
  Carboniferous 
  bedvS, 
  which 
  

   appear 
  wherever 
  erosion 
  or 
  other 
  causes 
  have 
  made 
  it 
  possible 
  for 
  them 
  

   to 
  do 
  so. 
  ]S[ortheast 
  of 
  station 
  Sisoneof 
  the 
  isolated 
  volcanicmouutaius, 
  

   and 
  there 
  may 
  be 
  placed 
  the 
  eastern 
  border 
  of 
  the 
  red 
  sandstone. 
  It 
  

   runs 
  from 
  there 
  toward 
  the 
  Spanish 
  Peaks, 
  and 
  is 
  covered 
  by 
  the 
  vol- 
  

   canic 
  rock 
  composing- 
  them. 
  Along 
  the 
  east 
  side 
  of 
  the 
  Sangre 
  de 
  

   Cristo 
  it 
  continues, 
  resting 
  first 
  on 
  the 
  metamorphic 
  granite, 
  then 
  on 
  

   the 
  Lower 
  Carboniferous 
  of 
  Trinchera 
  Peak. 
  All 
  that 
  region 
  lying 
  be- 
  

   tween 
  Indian 
  Creek 
  Pass 
  and 
  the 
  Spanish 
  Peaks 
  is 
  covered 
  by 
  it, 
  and 
  

   there 
  it 
  has 
  a 
  steady 
  easterly 
  dip 
  of 
  8° 
  to 
  12°. 
  Descending 
  on 
  one 
  of 
  

   the 
  ridges 
  from 
  the 
  pass 
  towards 
  the 
  headwaters 
  of 
  Arapaho 
  Creek, 
  

   a 
  rather 
  curious 
  case 
  of 
  erosion 
  was 
  noticed 
  in 
  the 
  sandstone. 
  Stand- 
  

   ing 
  perfectly 
  isolated, 
  near 
  the 
  crest 
  of 
  the 
  small 
  ridge 
  was 
  a 
  block 
  of 
  

   red 
  sandstone, 
  about 
  10 
  to 
  12 
  feet 
  in 
  height. 
  Near 
  the 
  center 
  of 
  it 
  a 
  

   natural 
  doorway 
  was 
  seen, 
  almost 
  high 
  enough 
  to 
  admit 
  of 
  a 
  man's 
  

   passing 
  through, 
  while 
  a 
  little 
  higher 
  up 
  was 
  another 
  smaller 
  open- 
  

   ing. 
  Considering 
  the 
  thickness 
  of 
  the 
  rock, 
  it 
  seemed 
  curious 
  at 
  first 
  

   by 
  what 
  agency 
  those 
  excavations 
  could 
  have 
  been 
  made, 
  but 
  upon 
  

   closer 
  observation 
  a 
  vertical 
  crack 
  was 
  discovered, 
  which 
  split 
  the 
  entire 
  

   bowlder. 
  It 
  was 
  evident, 
  therefore, 
  that 
  the 
  water 
  accumulating 
  therein 
  . 
  

   had 
  gradually 
  disintegrated 
  the 
  solter 
  layers 
  of 
  sandstone, 
  antl, 
  proba- 
  

   bly 
  materially 
  aided 
  by 
  frost, 
  succeeded 
  in 
  gradually 
  splintering 
  off 
  such 
  

   portions 
  as 
  would 
  most 
  readily 
  yield. 
  The 
  harder 
  strata, 
  the 
  one 
  dividing 
  

   the 
  two 
  perforations, 
  and 
  the 
  other 
  forming 
  the 
  roof, 
  had 
  thus 
  far 
  re- 
  

   sisted 
  the 
  influences 
  that 
  carried 
  away 
  other 
  portions 
  throughout 
  the 
  

   entire 
  thickness 
  of 
  the 
  bowlder. 
  This 
  process 
  of 
  excavation 
  throws 
  

   some 
  additional 
  light 
  on 
  the 
  formation 
  of 
  sandstone 
  caves, 
  and 
  of 
  the 
  

   ''bridges," 
  and 
  ''arches," 
  that 
  are 
  so 
  frequently 
  met 
  with 
  in 
  regions 
  

   where 
  sandstone 
  abounds. 
  A 
  protecting 
  cap 
  for 
  the 
  cavity 
  is, 
  in 
  an 
  

   instance 
  of 
  this 
  kind, 
  an 
  indispensable 
  necessity. 
  This 
  was 
  observed 
  

   near 
  station 
  120, 
  which 
  is 
  located 
  on 
  the 
  red 
  sandstone 
  of 
  the 
  ridge 
  men- 
  

   tioned 
  at 
  an 
  elevation 
  of 
  9,560 
  feet. 
  / 
  

  

  Descending 
  into 
  the 
  valley 
  we 
  are 
  confronted 
  by 
  a 
  vertical 
  wall 
  of 
  white 
  

   sandstone. 
  As 
  we 
  approach 
  it, 
  we 
  find 
  that 
  the 
  dip 
  of 
  the 
  red 
  sandstone 
  

   becomes 
  steeper 
  and 
  steeper, 
  until 
  it 
  appears 
  to 
  e 
  conformable 
  with 
  that 
  

   of 
  the 
  white. 
  Eed 
  shales 
  compose 
  the 
  strata 
  nearest 
  to 
  this 
  sandstone, 
  

   and 
  they 
  have 
  permitted 
  a 
  narrow 
  valley 
  to 
  be 
  eroded 
  parallel 
  to 
  their 
  

   strike. 
  Judging 
  from 
  lithological 
  characters 
  alone, 
  I 
  should 
  unhesi- 
  

   tatingly 
  have 
  pronounced 
  this 
  white 
  sandstone 
  to 
  be 
  Cretaceous 
  and 
  to 
  

   belong 
  to 
  the 
  lowest 
  group. 
  Upon 
  examination, 
  however, 
  it 
  was 
  found 
  

   that 
  the 
  main 
  body 
  of 
  Spanish 
  Peak 
  West 
  was 
  composed 
  of 
  red 
  Car- 
  

   boniferous 
  sandstone. 
  It 
  therefore 
  became 
  a 
  matter 
  of 
  extreme 
  difii- 
  

   culty 
  to 
  decide, 
  whether 
  this 
  was 
  really 
  Cretaceous, 
  or 
  merely 
  an 
  inter- 
  

   stratuni 
  of 
  white 
  sandstone 
  in 
  the 
  red. 
  No 
  fossils 
  could 
  be 
  found. 
  Con- 
  

   tinuing 
  our 
  explorations 
  to 
  the 
  south 
  and 
  southeast, 
  it 
  was 
  observed 
  

   that 
  the 
  white 
  sandstone 
  continued 
  in 
  an 
  almost 
  straight, 
  though 
  at 
  

   places 
  broken, 
  line 
  on 
  to 
  Costilla 
  Peak, 
  a 
  distance 
  of 
  about 
  thirty 
  six 
  

   miles. 
  It 
  was 
  furthermore 
  observed, 
  that 
  at 
  its 
  southern 
  exposures 
  it 
  

   was 
  accompanied 
  by 
  gray 
  shales 
  containing 
  Inocerami 
  and 
  Ostrecc. 
  In. 
  

   the 
  neighborhood 
  of 
  Spanish 
  Peak 
  West 
  (station 
  121), 
  no 
  other 
  Creta- 
  

   ceous 
  could 
  be 
  found, 
  save 
  the 
  continuous 
  area 
  near 
  station 
  123. 
  Itw^ill 
  be 
  

   remembered 
  that 
  the 
  Spanish 
  Peaks 
  are 
  the 
  only 
  high 
  mountains 
  rising 
  

   from 
  the 
  surrounding 
  sedimentaries 
  of 
  that 
  locality, 
  and 
  that 
  they 
  are 
  

   partly 
  (West 
  Spanish) 
  or 
  wholly 
  (East 
  Spanish) 
  volcanic. 
  In 
  view 
  of 
  

   these 
  facts 
  and 
  in 
  the 
  absence 
  of 
  all 
  fossils 
  that 
  might 
  render 
  a 
  decision 
  

   positive, 
  I 
  have 
  concluded 
  to 
  regard 
  this 
  white 
  sandstone 
  as 
  Cretaceous. 
  

  

  