﻿120 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  A 
  section 
  (Section 
  IV) 
  running 
  from 
  station 
  119 
  to 
  station 
  121 
  will 
  give 
  

   an 
  idea 
  of 
  the 
  present 
  position 
  of 
  the 
  strata. 
  Granite 
  (a) 
  forms 
  the 
  base 
  

   for 
  the 
  red 
  sandstone 
  (b) 
  to 
  rest 
  upon. 
  This 
  latter 
  dips 
  eastward 
  at 
  an 
  

   angle 
  of 
  about 
  18° 
  to 
  25°, 
  but 
  as 
  we 
  approach 
  the 
  valley 
  the 
  steepness 
  

   of 
  the 
  dip 
  increases, 
  until 
  it 
  has 
  become 
  almost 
  vertical. 
  In 
  the 
  valley, 
  

   among 
  the 
  readily 
  decomj)osing 
  red 
  shales 
  (c) 
  it 
  is 
  very 
  much 
  obscured, 
  

   and 
  when 
  next 
  we 
  liave 
  a 
  good 
  view 
  of 
  it, 
  it 
  is 
  in 
  the 
  vertical 
  wall 
  of 
  

   ^vhite 
  sandstone 
  {d). 
  Nearest 
  to 
  this 
  sandstone, 
  on 
  its 
  east 
  side, 
  red 
  

   shales 
  and 
  shaly 
  sandstones 
  again 
  appear, 
  dipping 
  eastward 
  at 
  an 
  angle 
  

   of 
  70° 
  to 
  80°. 
  Soon 
  a 
  trachitic 
  eruption 
  has 
  broken 
  through 
  them, 
  forming 
  

   a 
  prominent 
  hill 
  (e). 
  After 
  that 
  the 
  red 
  sandstones 
  (/), 
  for 
  we 
  find 
  noth- 
  

   ing 
  but 
  such 
  now, 
  begin 
  to 
  dip 
  more 
  gently, 
  become 
  horizontal 
  eventually, 
  

   and 
  near 
  the 
  summitof 
  Spanish 
  Peak 
  west, 
  have 
  a 
  westerly 
  dip 
  of 
  G° 
  to 
  8°. 
  

   Numerous 
  dikes 
  {[/) 
  traverse 
  the 
  sandstone, 
  and 
  on 
  the 
  summit 
  of 
  the 
  

   peak 
  it 
  is 
  capped 
  by 
  trachyte, 
  which 
  stands 
  in 
  connection 
  with 
  a 
  number 
  

   of 
  dikes 
  apparently 
  issuing 
  from 
  one 
  main 
  center. 
  Assuming 
  now 
  that 
  

   The 
  red 
  sandstone 
  had 
  its 
  original 
  dip 
  to 
  the 
  east 
  (8° 
  to 
  15°), 
  and 
  that 
  

   a 
  portion 
  of 
  it 
  was 
  covered 
  by 
  Cretaceous 
  sandstone, 
  if 
  we 
  could 
  get 
  the 
  

   force 
  to 
  uplift, 
  east 
  of 
  the 
  Cretaceous 
  outcrop, 
  the 
  massive 
  sandstone 
  

   beds, 
  curve 
  them, 
  and 
  overturn 
  tliem, 
  so 
  as 
  to 
  be 
  apparently 
  conform- 
  

   able 
  with 
  its 
  secondary 
  position, 
  we 
  would 
  obtain 
  the 
  result 
  observed 
  

   at 
  the 
  present 
  time. 
  Whether 
  the 
  trachytic 
  mass 
  alone 
  was 
  accom- 
  

   panied 
  by 
  or 
  the 
  cause 
  of 
  that 
  force, 
  or 
  whether 
  it 
  was 
  aided 
  by 
  some 
  

   other 
  vertically-acting 
  power 
  which 
  ])roduced 
  its 
  most 
  marked 
  results 
  

   at 
  the 
  point 
  of 
  least 
  resistance, 
  would 
  then 
  remain 
  in 
  question. 
  As 
  a 
  

   fact 
  it 
  may 
  be 
  stated, 
  that 
  while 
  West 
  Spanish 
  is 
  composed 
  mainly 
  of 
  

   sandstone, 
  and 
  only 
  a 
  small 
  portion 
  of 
  the 
  volcanic 
  material, 
  East 
  

   Spanish 
  is 
  entirely 
  volcanic. 
  

  

  In 
  the 
  field 
  I 
  held 
  the 
  view, 
  explaining 
  the 
  enormous 
  increase 
  in 
  

   thickness 
  of 
  the 
  sandstones 
  at 
  Spanish 
  Peaks, 
  by 
  the 
  acceptation 
  of 
  an 
  

   overturn 
  of 
  the 
  strata. 
  As 
  lias 
  been 
  mentioned 
  above, 
  the 
  stratification 
  

   near 
  the 
  narrow 
  Cretaceous 
  outci^op 
  is 
  very 
  much 
  obscured, 
  and 
  no 
  ab- 
  

   solutely 
  definite 
  knowledge 
  could 
  there 
  be 
  obtained. 
  Since 
  studying 
  up 
  

   the 
  case, 
  however, 
  I 
  have 
  come 
  to 
  the 
  conclusion 
  that 
  the 
  disturbance 
  

   there 
  produced 
  is 
  not 
  that 
  of 
  an 
  overturn, 
  but 
  of 
  a 
  fault. 
  This 
  fault 
  

   has 
  occurred 
  immediately 
  east 
  of 
  the 
  Cretaceous 
  outcrop, 
  has 
  elevated 
  

   the 
  sandstones 
  of 
  the 
  Spanish 
  Peaks, 
  and 
  has 
  given 
  rise 
  to 
  changes 
  in 
  

   the 
  inclination 
  of 
  their 
  strata. 
  Its 
  vertical 
  extent 
  amounts 
  to 
  more 
  than 
  

   2,000 
  feet. 
  It 
  is 
  highly 
  probable 
  that 
  the 
  anticlinal 
  fold 
  observed 
  near 
  

   station 
  G2 
  of 
  1874, 
  may 
  be 
  in 
  connection 
  with 
  this 
  extensive 
  fault. 
  

   Considering 
  the 
  mass 
  of 
  volcanic 
  material 
  that 
  has 
  been 
  ejected 
  at 
  

   Spanish 
  Peaks, 
  I 
  conclude 
  that 
  the 
  sandstone 
  of 
  the 
  two 
  peaks 
  were 
  

   raised 
  from 
  their 
  normal 
  position 
  so 
  as 
  to 
  assume 
  that 
  which 
  they 
  at 
  

   present 
  occupy. 
  Injection 
  of 
  volcanic 
  masses 
  between 
  the 
  sandstone 
  

   strata 
  may 
  account 
  for 
  the 
  increased 
  thickness 
  of 
  the 
  latter. 
  It 
  is 
  to 
  

   be 
  regretted 
  that 
  the 
  key-point 
  east 
  of 
  the 
  Cretaceous 
  outcrop 
  was 
  

   so 
  much 
  obscured 
  by 
  detritus 
  and 
  timber. 
  During 
  the 
  disturbance 
  

   of 
  the 
  strata 
  there 
  were, 
  of 
  course, 
  innumerable 
  cracks 
  formed, 
  which, 
  

   owing, 
  perhaps, 
  to 
  the 
  great 
  thickness 
  of 
  the 
  sandstone, 
  often 
  run 
  in 
  

   very 
  straight 
  lines. 
  The 
  liquid 
  or 
  plastic 
  volcanic 
  material 
  entered 
  the 
  

   fissures, 
  and 
  now 
  forms 
  the 
  walls 
  that 
  often 
  are 
  over 
  several 
  hundred 
  

   feet 
  in 
  height. 
  In 
  the 
  ])ortion 
  of 
  this 
  chapter 
  devoted 
  to 
  the 
  volcanic 
  

   rocks 
  of 
  the 
  region, 
  this 
  will 
  be 
  more 
  fully 
  discussed. 
  

  

  A 
  series 
  of 
  very 
  interesting 
  metamorphoses 
  may 
  be 
  observed 
  in 
  the 
  

   red 
  sandstone 
  while 
  ascending 
  station 
  121. 
  Before 
  lea,ving 
  the 
  un- 
  

   changed 
  sandstone, 
  bowlders 
  of 
  quartzite 
  and 
  a 
  very 
  compact 
  granite, 
  

  

  