﻿122 
  EEPOET 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  high 
  hill 
  (d) 
  composed 
  of 
  trachyte. 
  On 
  the 
  western 
  side 
  its 
  bound- 
  

   aries 
  are 
  parallel 
  with 
  the 
  line 
  of 
  the 
  second 
  ridge, 
  but 
  on 
  the 
  south- 
  

   east 
  it 
  has 
  overflowed 
  a 
  portion 
  of 
  the 
  younger 
  strata. 
  At 
  first 
  

   sight 
  this 
  illustration 
  will 
  suggest 
  an 
  anticlinal 
  fold, 
  but 
  it 
  is 
  not 
  

   one. 
  Not 
  a 
  trace 
  of 
  the 
  white 
  sandstone 
  can 
  be 
  found 
  on 
  the 
  east 
  

   side 
  of 
  the 
  valley, 
  while 
  none 
  of 
  that 
  observed 
  there 
  occurs 
  on 
  the 
  

   west. 
  This 
  extraordinary 
  arrangement 
  of 
  strata 
  does 
  not 
  occur 
  for 
  

   any 
  length 
  of 
  distance, 
  because 
  a 
  little 
  farther 
  north 
  both 
  the 
  Carbon- 
  

   iferous 
  and 
  Cretaceous 
  strata 
  regain 
  their 
  original 
  easterly 
  dip. 
  Tak- 
  

   ing 
  a 
  section 
  (Section 
  V) 
  through 
  the 
  first 
  ridge 
  and 
  the 
  trachytic 
  

   hill, 
  we 
  find 
  the 
  arrangement 
  of 
  the 
  strata 
  as 
  follows 
  : 
  About 
  1,500 
  

   feet 
  of 
  the 
  red 
  sandstone 
  {a) 
  dip 
  at 
  an 
  angle 
  of 
  35° 
  to 
  the 
  west. 
  Five 
  

   interstrata 
  of 
  whitish 
  sandstone 
  (&) 
  were 
  observed. 
  They 
  diifer 
  in 
  noth- 
  

   ing 
  from 
  the 
  other, 
  save 
  in 
  their 
  color, 
  which 
  is 
  not 
  the 
  pure 
  or 
  the 
  yel- 
  

   lowish 
  white 
  usually 
  observed 
  in 
  Lower 
  Cretaceous 
  sandstones, 
  but 
  a 
  

   more 
  mottled 
  reddish 
  or 
  brownish 
  white. 
  Exposed 
  entirely 
  on 
  the 
  west 
  

   side 
  we 
  then 
  find 
  a 
  sandstone 
  (c), 
  probably 
  200 
  to 
  350 
  feet 
  in 
  thickness. 
  

   It 
  is 
  quartzitic 
  in 
  parts, 
  of 
  fine 
  grain, 
  lithologically 
  totally 
  distinct 
  from 
  

   the 
  superincumbent 
  ones. 
  A 
  large 
  mass 
  of 
  small 
  bowlders, 
  gravel, 
  and 
  

   silt 
  has 
  been 
  washed 
  into 
  the 
  valley 
  (fZ), 
  from 
  the 
  red 
  sandstones, 
  so 
  

   that 
  any 
  attempt 
  at 
  discovering 
  the 
  nature 
  of 
  underlying 
  beds 
  is 
  ren- 
  

   dered 
  ineffectual. 
  I 
  did 
  not 
  succeed 
  in 
  finding 
  there 
  a 
  single 
  outcrop 
  

   of 
  strata 
  in 
  positu. 
  It 
  seems 
  probable, 
  however, 
  that 
  shales 
  of 
  some 
  

   kind 
  have 
  permitted 
  the 
  formation 
  of 
  this 
  valley, 
  on 
  account, 
  first, 
  

   of 
  its 
  peculiar 
  shape 
  and 
  topographical 
  features, 
  and 
  secondly, 
  because 
  

   such 
  shales 
  were 
  discovered 
  about 
  18 
  miles 
  farther 
  north 
  in 
  the 
  contin- 
  

   uation 
  of 
  the 
  valley. 
  The 
  trachytic 
  hill 
  {d) 
  stands 
  out 
  prominently 
  at 
  

   this 
  point, 
  sharp 
  and 
  well 
  cut, 
  though 
  farther 
  south 
  it 
  joins 
  more 
  closely 
  

   the 
  eastern 
  bluff. 
  Beyond 
  it 
  is 
  the 
  third 
  ridge 
  (e) 
  composed 
  of 
  yellow 
  

   sandstones 
  and 
  shales 
  that 
  will 
  be 
  treated 
  of 
  in 
  chapter 
  5. 
  Such 
  is 
  the 
  

   appearance 
  of 
  a 
  section 
  at 
  this 
  point, 
  without 
  any 
  reference 
  to 
  the 
  

   causes 
  that 
  have 
  produced 
  the 
  effect 
  observed. 
  Another 
  section, 
  (Sec- 
  

   tion 
  VI) 
  made 
  after 
  having 
  seen 
  the 
  entire 
  valley, 
  may 
  give 
  some 
  idea 
  

   of 
  the 
  dynamics 
  involved 
  in 
  placing 
  the 
  strata 
  into 
  their 
  present 
  posi- 
  

   tion. 
  The 
  third 
  ridge 
  {ee) 
  is 
  composed 
  of 
  sandstones 
  and 
  shales 
  belong- 
  

   ing 
  to 
  a 
  Post-Cretaceous 
  period, 
  which 
  dip 
  eastward 
  at 
  an 
  angle 
  of 
  10° 
  

   to 
  15°, 
  underlying 
  Cretaceous 
  and 
  Carboniferous 
  beds, 
  therefore, 
  must 
  

   have 
  been 
  moved 
  at 
  one 
  time 
  westward 
  and 
  overturned, 
  in 
  order 
  to 
  as- 
  

   sume 
  their 
  present 
  position. 
  It 
  will 
  be 
  noticed 
  that 
  this 
  overturn 
  ex- 
  

   tends 
  but 
  a 
  short 
  distance 
  beyond 
  the 
  superficial 
  appearance 
  of 
  the 
  vol- 
  

   canic 
  material, 
  and 
  that 
  soon 
  after 
  that 
  has 
  disappeared 
  a 
  return 
  to 
  the 
  

   normal 
  dip 
  takes 
  place. 
  It 
  is 
  an 
  analogous 
  case 
  to 
  that 
  near 
  the 
  Spanish 
  

   Peaks, 
  where 
  volcanics,too, 
  play 
  so 
  important 
  a 
  part. 
  Were 
  it 
  not 
  for 
  

   the 
  fact 
  that 
  the 
  white 
  Cretaceous 
  sandstone 
  can 
  readily 
  be 
  traced 
  

   throughout 
  the 
  entire 
  distance, 
  the 
  explanation 
  of 
  this 
  phenomenon 
  

   might 
  prove 
  to 
  be 
  very 
  different. 
  More 
  will 
  be 
  said 
  about 
  the 
  occur- 
  

   rence 
  and 
  surroundings 
  of 
  the 
  latter 
  in 
  the 
  discussion 
  of 
  the 
  Cretaceous 
  

   formation 
  of 
  the 
  district 
  to 
  which 
  this 
  chapter 
  is 
  devoted. 
  

  

  Besides 
  those 
  given 
  above, 
  no 
  outcrops 
  of 
  Carboniferous 
  beds 
  were 
  ob- 
  

   served 
  in 
  the 
  district 
  under 
  consideration. 
  It 
  will 
  be 
  seen, 
  that 
  here, 
  

   too, 
  as 
  farther 
  north, 
  they 
  form 
  a 
  large 
  portion 
  of 
  the 
  Sangre 
  de 
  Cristo 
  

   Eange, 
  and 
  although 
  not 
  reaching 
  very 
  great 
  elevations, 
  with 
  the 
  ex- 
  

   ception 
  of 
  the 
  Trinchera 
  group, 
  they 
  are 
  of 
  great 
  importance 
  in 
  the 
  

   structure 
  of 
  the 
  range. 
  It 
  will 
  furthermore 
  be 
  observed 
  that, 
  in 
  the 
  

   vicinity 
  of 
  the 
  greatest 
  disturbances 
  to 
  which 
  these 
  strata 
  have 
  been 
  

   subjected, 
  we 
  find 
  the 
  best 
  passes 
  across 
  the 
  mountains. 
  At 
  Sangre 
  

  

  