﻿ENDLicH] 
  HUERFANO 
  VOLCANICS. 
  131 
  

  

  Huerfano 
  or 
  in 
  the 
  Spanish 
  group. 
  As 
  the 
  average 
  character 
  the 
  fol- 
  

   lowing 
  description 
  may 
  serve: 
  The 
  rock 
  has 
  a 
  dark 
  grey 
  color, 
  pro- 
  

   duced 
  by 
  finely 
  disseminated 
  magnetite, 
  and 
  is 
  microcrystalline. 
  Thiii 
  

   seams 
  of 
  epidote 
  occur 
  in 
  it. 
  Crystals 
  of 
  sanidite 
  are 
  partly 
  fresh, 
  

   partly 
  decomposed, 
  in 
  the 
  latter 
  case 
  opaque. 
  A 
  green 
  chloritic 
  mineral 
  

   occurs 
  in 
  minute 
  crystals, 
  dispersed 
  throughout 
  the 
  entire 
  mass. 
  

  

  The 
  western 
  spur 
  of 
  the 
  range, 
  the 
  one 
  upon 
  which 
  station 
  108 
  was 
  

   made, 
  I 
  regard 
  as 
  the 
  true 
  continuation 
  of 
  the 
  Saugre 
  de 
  Cristo, 
  topo- 
  

   graphically 
  considered. 
  From 
  a 
  geological 
  point 
  of 
  view 
  tbe 
  eastern 
  

   one 
  would 
  probably 
  be 
  chosen, 
  as 
  it 
  is 
  here, 
  that 
  the 
  formations 
  com- 
  

   posing 
  the 
  range 
  farther 
  north 
  are 
  fully 
  represented. 
  Red 
  Carbonifer- 
  

   ous 
  sandstone, 
  which 
  forms 
  so 
  important 
  a 
  feature 
  on 
  both 
  sides 
  of 
  the 
  

   range, 
  is 
  wanting 
  on 
  the 
  western 
  side, 
  while 
  it 
  is 
  found 
  on 
  the 
  other, 
  

   and 
  there 
  gives 
  rise 
  to 
  the 
  formation 
  of 
  mountains 
  of 
  considerable 
  size. 
  

   At 
  Costilla 
  Pass, 
  the 
  direct 
  continuation 
  of 
  the 
  range 
  is 
  broken, 
  and, 
  

   it 
  seems 
  to 
  me, 
  it 
  must 
  then 
  be 
  looked 
  for 
  in 
  the 
  western 
  branch. 
  Of 
  

   the 
  isolated 
  patches 
  north 
  of 
  tbe 
  main 
  area 
  thereis 
  the 
  oneleading 
  toward 
  

   station 
  113. 
  Trachyte 
  there 
  occupies 
  a 
  number 
  of 
  the 
  higher 
  points 
  

   overlying 
  granite 
  or 
  Carboniferous 
  sandstone. 
  Southwest 
  of 
  station 
  

   113 
  it 
  forms 
  a 
  small 
  plateau, 
  above 
  timber-line, 
  and 
  from 
  there 
  descends 
  

   southward 
  into 
  the 
  valley. 
  It 
  is 
  not 
  in 
  direct 
  connection 
  with 
  the 
  tra- 
  

   chyte 
  of 
  station 
  114, 
  but 
  approaches 
  it 
  within 
  a 
  few 
  miles, 
  and 
  is, 
  no 
  

   doubt, 
  the 
  same 
  flow. 
  As 
  the 
  general 
  dip 
  of 
  the 
  metamorphics, 
  so 
  is 
  

   the 
  general 
  dip 
  of 
  the 
  volcanic 
  rocks 
  of 
  this 
  region 
  a 
  westerly 
  one, 
  ex- 
  

   cept 
  near 
  station 
  111, 
  where 
  the 
  flows 
  extend 
  eastward. 
  In 
  the 
  southern 
  

   group 
  there 
  is 
  but 
  little 
  variety 
  in 
  the 
  lithological 
  character 
  of 
  the 
  lay- 
  

   ers 
  ; 
  they 
  would 
  belong, 
  if 
  compared, 
  to 
  No. 
  3, 
  trachyte 
  of 
  the 
  San 
  Juan 
  

   country.* 
  

  

  The 
  average 
  thickness 
  here 
  may 
  be 
  stated 
  at 
  1,000 
  to 
  1,500 
  feet, 
  al- 
  

   though 
  locally 
  this 
  estimate 
  is 
  greatly 
  over 
  and 
  under 
  reached. 
  It 
  would 
  

   be 
  of 
  interest 
  to 
  make 
  careful 
  comparisons 
  in 
  detail 
  of 
  each 
  successive 
  

   flow 
  or 
  layer, 
  and 
  compare 
  them 
  with 
  the 
  analogous 
  or 
  parallel 
  beds 
  of 
  

   the 
  Sawatch 
  Range. 
  So 
  tar 
  as 
  could 
  be 
  seen 
  in 
  the 
  comparatively 
  hur- 
  

   ried 
  examination 
  could 
  that 
  only 
  be 
  made, 
  no 
  positive 
  identification 
  of 
  

   these 
  strata 
  with 
  those 
  farther 
  west 
  will 
  be 
  possible. 
  

  

  On 
  the 
  Huerfano, 
  near 
  Badito, 
  station 
  141 
  is 
  located 
  on 
  a 
  Cretaceous 
  

   bluff, 
  covered 
  by 
  basalt. 
  Its 
  elevation 
  is 
  6,952 
  feet. 
  The 
  regular 
  bluff 
  

   trends 
  from 
  northeast 
  to 
  southwest, 
  has 
  a 
  comparatively 
  flat 
  top 
  with 
  

   some 
  rising 
  hills 
  on 
  its 
  summit. 
  Immediately 
  south 
  of 
  it 
  is 
  another 
  bluff 
  

   of 
  the 
  same 
  character. 
  They 
  are 
  both 
  in 
  a 
  line 
  with 
  stations 
  5 
  and 
  7, 
  

   and 
  probably 
  belong 
  to 
  the 
  same 
  system 
  of 
  eruption, 
  although 
  the 
  rock 
  is 
  

   younger. 
  Northeast 
  of 
  station 
  5 
  is 
  an 
  isolated 
  hill, 
  almost 
  dome-shaped, 
  

   which 
  I 
  have 
  named 
  Muralla 
  Peak, 
  with 
  a 
  number 
  of 
  dikes 
  leading 
  to- 
  

   ward 
  it. 
  Probably 
  the 
  main 
  body 
  of 
  this 
  hill 
  is 
  trachytic, 
  as 
  those 
  far- 
  

   ther 
  westare, 
  butthedikes 
  are 
  almost 
  basaltic, 
  and 
  they 
  seem 
  tohave 
  been 
  

   formed 
  by 
  the 
  same 
  material 
  that 
  covers 
  the 
  two 
  blutt'sin 
  question, 
  and 
  

   probably 
  at 
  the 
  same 
  time. 
  On 
  the 
  second 
  blufl' 
  three 
  conical 
  rises 
  

   may 
  be 
  observed, 
  that 
  apparently 
  indicate 
  the 
  points 
  of 
  outflow. 
  Water 
  

   has 
  carried 
  on 
  erosion 
  very 
  successfully 
  in 
  that 
  region, 
  and 
  a 
  large 
  por- 
  

   tion 
  of 
  it, 
  that 
  no 
  doubt 
  atone 
  time 
  was 
  covered 
  by 
  volcanic 
  strata, 
  is 
  now 
  

   denuded 
  and 
  shows 
  Cretaceous 
  beds. 
  Betw'een 
  the 
  two 
  bluffs 
  the 
  con- 
  

   nection 
  of 
  the 
  basalt 
  is 
  very 
  slight, 
  although 
  they 
  are 
  but 
  a 
  very 
  short 
  

   distance 
  apart. 
  Small 
  remnants 
  of 
  the 
  more 
  extensive 
  basaltic 
  areas 
  

   occur 
  in 
  a 
  few 
  hills 
  trending 
  toward 
  the 
  larger 
  volcanic 
  group 
  west. 
  

   All 
  of 
  them 
  either 
  cover 
  or 
  penetrate 
  Cretaceous 
  beds. 
  

  

  *Eeport 
  United 
  States 
  Geological 
  Survey, 
  J874, 
  p. 
  196. 
  

  

  