﻿ENDLicH] 
  SANGRE 
  DE 
  CEISTO 
  SILURIAN. 
  113 
  

  

  iug 
  off 
  steeply 
  into 
  San 
  Luis 
  Valley. 
  Their 
  edge 
  runs 
  nearly 
  due 
  south, 
  

   and 
  their 
  slopes 
  mark 
  the 
  presence 
  of 
  a 
  strip 
  of 
  inetatnorphic 
  granite, 
  

   while 
  the 
  summit 
  of 
  the 
  range 
  is 
  composed 
  of 
  trachyte. 
  Station 
  108 
  is 
  

   located 
  upon 
  the 
  latter, 
  12,467 
  feet 
  high. 
  No 
  definite 
  data 
  were 
  ob- 
  

   tained 
  referring 
  to 
  the 
  dip 
  of 
  this 
  granite, 
  as 
  it 
  is 
  very 
  much 
  obscured 
  

   by 
  cleavage. 
  It 
  seems, 
  however, 
  to 
  dip 
  westward. 
  Many 
  varieties 
  

   were 
  noticed 
  here, 
  also, 
  an 
  evidence 
  in 
  favor 
  of 
  the 
  assumption 
  that 
  claims 
  

   a 
  common 
  origin 
  for 
  the 
  metamorphics 
  of 
  the 
  Sangre 
  de 
  Cristo 
  chain, 
  

   and, 
  so 
  far 
  as 
  is 
  possible 
  to 
  determine, 
  a 
  synchronous 
  metamori)hosis. 
  

   Bands 
  of 
  typical 
  gneiss 
  alternate 
  at 
  places 
  with 
  micaceous 
  or 
  chloritic 
  

   schists. 
  Granite, 
  from 
  the 
  fine-grained 
  to 
  the 
  coarsest 
  variety, 
  is 
  found, 
  

   apparently 
  without 
  any 
  definite 
  system 
  of 
  arrangement. 
  The 
  coarse- 
  

   grained 
  is 
  i3revalent, 
  containing 
  often 
  good-si2ied 
  sheets 
  of 
  mica 
  and 
  

   large 
  masses 
  of 
  quartz 
  and 
  feldspar 
  (orthoclase). 
  Quartz 
  veins 
  trav- 
  

   erse 
  the 
  granite 
  in 
  several 
  directions, 
  of 
  which, 
  perhaps, 
  the 
  strike 
  

   northeast 
  to 
  southwest 
  may 
  be 
  regarded 
  as 
  the 
  most 
  frequent. 
  Indica- 
  

   tions 
  of 
  ore 
  were 
  found 
  in 
  these 
  veins, 
  and 
  will 
  be 
  mentioned 
  at 
  the 
  

   proper 
  place. 
  With 
  this 
  the 
  metamorphic 
  area 
  of 
  the 
  region 
  which 
  is 
  

   discussed 
  in 
  this 
  chapter 
  is 
  ended. 
  A 
  synopsis 
  of 
  the 
  facts 
  observed 
  

   presents 
  the 
  conclusion 
  that 
  the 
  metamorphics 
  of 
  the 
  lower 
  Sangre 
  de 
  

   Cristo 
  owe 
  their 
  existence 
  to 
  an 
  alteration 
  Of 
  the 
  

  

  SILURIAN. 
  

  

  North 
  of 
  the 
  Arkansas 
  Eiver 
  the 
  Silurian 
  formation 
  occurs.* 
  From 
  

   there 
  it 
  crosses 
  the 
  river 
  toward 
  the 
  south, 
  and 
  is 
  last 
  seen 
  as 
  such 
  near 
  

   the 
  northern 
  end 
  of 
  the 
  Sangre 
  de 
  Cristo 
  Eange, 
  In 
  its 
  strati 
  graphical 
  

   relations 
  it 
  is 
  conformable 
  with 
  the 
  overlying, 
  younger 
  formations, 
  

   wherever 
  it 
  has 
  been 
  there 
  observed. 
  We 
  have 
  evidence, 
  therefore, 
  

   that 
  it 
  exists 
  but 
  a 
  comparatively 
  short 
  distance 
  from 
  the 
  j'ange, 
  cov- 
  

   ered 
  by 
  the 
  Carboniferous 
  5 
  among 
  the 
  latter 
  the 
  strata 
  of 
  red 
  sand- 
  

   stones 
  that 
  belong 
  thereto. 
  Going 
  south 
  into 
  the 
  range, 
  we 
  find 
  that 
  

   the 
  sandstones 
  still 
  remain, 
  form 
  a 
  large 
  bulk 
  of 
  the 
  mountains 
  in 
  fact, 
  

   but 
  the 
  Silurian 
  and 
  the 
  lowest 
  Carboniferous 
  have 
  disappeared. 
  At 
  

   the 
  same 
  time, 
  we 
  observe 
  that 
  the 
  metamorphic 
  rocks 
  of 
  the 
  range 
  

   differ 
  from 
  those 
  not 
  much 
  farther 
  north, 
  where 
  they 
  underlie 
  the 
  Silu- 
  

   rian. 
  So 
  far 
  as 
  could 
  be 
  determined, 
  the 
  granites 
  and 
  schists 
  of 
  the 
  

   Sangre 
  de 
  Cristo 
  show 
  stratoid 
  relations 
  conformable 
  with 
  those 
  of 
  the 
  

   superincumbent 
  sedimentary 
  beds. 
  They 
  furthermore 
  form 
  the 
  " 
  core" 
  

   of 
  the 
  mountain 
  chain, 
  holding 
  the 
  same 
  relative 
  position 
  with 
  reference 
  

   to 
  younger 
  formations 
  that 
  Silurian 
  or 
  Dfevonian 
  would 
  hold. 
  It 
  seems 
  

   possible, 
  therefore, 
  that 
  during 
  the 
  progress 
  of 
  an 
  extensive 
  metamor- 
  

   phosis, 
  the 
  Silurian, 
  and 
  perhaps 
  lowest 
  Carboniferous 
  strata, 
  furnished 
  

   the 
  material 
  for 
  the 
  existence 
  of 
  our 
  present 
  granites, 
  gneisses, 
  and 
  

   schists 
  at 
  that 
  locality. 
  It 
  is, 
  so 
  far 
  as 
  I 
  know 
  the 
  region, 
  impossible 
  to 
  

   prove 
  any 
  hypothesis 
  of 
  tbis 
  kind, 
  but, 
  considering 
  the 
  analogous 
  oc- 
  

   currence, 
  the 
  absence 
  of 
  all 
  formations 
  older 
  than 
  the 
  Middle 
  Carbonif- 
  

   erous, 
  and 
  the 
  evidence 
  of 
  the 
  existence 
  of 
  this 
  older 
  formation 
  only 
  a 
  

   short 
  distance 
  farther 
  north, 
  I 
  think 
  the 
  assumption 
  is 
  entitled 
  to 
  further 
  

   investigation. 
  A 
  similar 
  case 
  was 
  observed 
  during 
  1874,t 
  but 
  in 
  that 
  

   instance 
  the 
  solution 
  was 
  by 
  far 
  easier 
  than 
  in 
  this 
  one. 
  

  

  * 
  Report 
  United 
  States 
  Geologjical 
  and 
  Geographical 
  Survey 
  1873, 
  p. 
  308. 
  

   t 
  Report 
  United 
  States 
  Geological 
  and 
  Geographical 
  Survey 
  1874, 
  p. 
  190. 
  

  

  8 
  G 
  S 
  

  

  