﻿128 
  EEPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  this 
  mountain 
  is 
  about 
  1,200 
  feet 
  in 
  thickness, 
  of 
  a 
  light-jellow 
  to 
  whit- 
  

   ish 
  color. 
  Paste 
  crypto- 
  crystalline 
  containing 
  very 
  bright, 
  minute 
  crys- 
  

   tals 
  of 
  sanidite. 
  Upon 
  exi)Osnre 
  it 
  assumes 
  a 
  light-brown 
  color, 
  due 
  to 
  

   the 
  presence 
  of 
  a 
  very 
  small 
  percentage 
  of 
  magnetite, 
  and 
  breaks 
  into 
  

   thin 
  fragments 
  and 
  slabs 
  that 
  have 
  a 
  serai-metallic 
  ring. 
  North 
  of 
  sta- 
  

   tion 
  4 
  is 
  another 
  smaller 
  hill, 
  of 
  almost 
  the 
  same 
  shape 
  and 
  general 
  ap- 
  

   X^earance. 
  Toward 
  the 
  west 
  the 
  volcanic 
  mass 
  has 
  flown 
  over 
  the 
  high 
  

   portion 
  of 
  country, 
  from 
  which 
  Sangre 
  de 
  Cristo 
  Creek 
  receives 
  a 
  con- 
  

   siderable 
  supply 
  of 
  water. 
  , 
  At 
  that 
  point 
  the 
  trachyte 
  covers 
  the 
  Car- 
  

   boniferous 
  strata. 
  A 
  little 
  east 
  of 
  south 
  from 
  station 
  4 
  is 
  station 
  5, 
  at 
  

   an 
  altitude 
  of 
  11,512 
  feet, 
  located 
  also 
  upon 
  trachyte. 
  It 
  is 
  identical 
  

   with 
  that 
  of 
  the 
  former. 
  Drawing 
  a 
  line 
  from 
  station 
  5 
  in 
  the 
  direction 
  

   north 
  25<^ 
  west, 
  it 
  will 
  be 
  found 
  that 
  the 
  three 
  mountains 
  thus 
  far 
  men- 
  

   tioned 
  stand 
  in 
  one 
  straight 
  row. 
  Judging 
  from 
  this 
  and 
  from 
  the 
  dike- 
  

   like 
  character 
  that 
  almost 
  all 
  the 
  eruptions 
  in 
  this 
  region 
  have, 
  I 
  should 
  

   suppose 
  that 
  this 
  was 
  merely 
  one 
  immense 
  dike, 
  disrupted 
  at 
  the 
  eleva- 
  

   tion 
  of 
  the 
  present 
  Cretaceous 
  sandstones 
  between 
  them. 
  It 
  seems 
  to 
  

   have 
  contained 
  more 
  volcanic 
  matter 
  than 
  was 
  required 
  to 
  fill 
  the 
  fis- 
  

   sure, 
  consequently 
  overflowed 
  both 
  to 
  the 
  westward 
  and 
  eastward. 
  As 
  

   it 
  is 
  the 
  case 
  near 
  station 
  4, 
  so 
  it 
  is 
  near 
  station 
  5. 
  Although 
  the 
  connec- 
  

   tion 
  now 
  is 
  broken, 
  and 
  the 
  Carboniferous 
  strata 
  covered 
  by 
  the 
  two 
  

   masses 
  have 
  appeared 
  between 
  them 
  in 
  Veta 
  Pass, 
  that 
  large 
  area 
  imme- 
  

   diately 
  south 
  of 
  Sangre 
  de 
  Cristo 
  Pass 
  was 
  in 
  connection 
  with 
  the 
  

   mountain 
  of 
  station 
  5. 
  From 
  the 
  section 
  through 
  the 
  pass 
  (Section 
  I) 
  it 
  

   is 
  evident 
  that 
  there, 
  too, 
  the 
  trachyte 
  reaches 
  to 
  considerable 
  depth, 
  and 
  

   is 
  at 
  the 
  same 
  time 
  of 
  the 
  same 
  lithological 
  constitution 
  as 
  its 
  two 
  eastern 
  

   neighbors. 
  It 
  seems 
  probable, 
  therefore, 
  that 
  a 
  number 
  of 
  these 
  huge 
  

   dikes 
  occur 
  here, 
  but 
  on 
  account 
  of 
  the 
  lava 
  having 
  flowed 
  from 
  one 
  to 
  the 
  

   other, 
  their 
  individual 
  outlines 
  have 
  been 
  lost. 
  Station 
  7 
  is 
  located 
  on 
  

   a 
  trachyte, 
  near 
  the 
  junction 
  of 
  Sangre 
  de 
  Cristo 
  and 
  Indian 
  Creeks, 
  

   8,967 
  feet 
  high. 
  This 
  appears 
  to 
  be 
  an 
  isolated 
  outflow, 
  separate 
  from 
  the 
  

   eastern 
  ones, 
  but 
  in 
  connection 
  with 
  that 
  a 
  few 
  miles 
  north 
  of 
  it. 
  In 
  

   mineralogical 
  and 
  physical 
  character 
  this 
  trachyte 
  differs 
  Irom 
  the 
  

   former. 
  It 
  is 
  brown, 
  almost 
  lilac 
  when 
  fresh, 
  contains 
  small 
  crystals 
  of 
  

   biotite 
  and 
  sanidite. 
  A 
  short 
  distance 
  below 
  the 
  station 
  it 
  can 
  be 
  ob- 
  

   served 
  overlying 
  the 
  metamorphic 
  granite 
  of 
  that 
  locality. 
  It 
  weath- 
  

   ers, 
  on 
  account 
  of 
  its 
  flows, 
  by 
  far 
  more 
  massively 
  than 
  the 
  eastern, 
  

   and 
  presents 
  more 
  the 
  character 
  of 
  that 
  found 
  on 
  the 
  west 
  side 
  of 
  San 
  

   Luis 
  Valley. 
  Only 
  for 
  a 
  short 
  distance 
  can 
  the 
  flows 
  be 
  traced 
  in 
  any 
  

   direction 
  j 
  then 
  they 
  thin 
  out 
  and 
  disappear. 
  It 
  can 
  be 
  observed, 
  as 
  a 
  

   rule, 
  that 
  the 
  trachytes 
  west 
  of 
  the 
  Sangre 
  de 
  Cristo 
  divide 
  have 
  a 
  dif- 
  

   ferent 
  character 
  from 
  those 
  east 
  of 
  it, 
  unless, 
  as 
  is 
  the 
  case 
  farther 
  

   south, 
  the 
  western 
  ones 
  have 
  flowed 
  over. 
  It 
  is 
  furthermore 
  noticeable 
  

   that 
  on 
  the 
  western 
  side 
  no 
  dikes, 
  neither 
  the 
  large 
  ones, 
  as 
  the 
  Sheep 
  

   Mountains, 
  nor 
  the 
  smaller 
  ones, 
  will 
  be 
  found, 
  although 
  but 
  a 
  few 
  miles 
  

   distant 
  they 
  occur 
  in 
  such 
  great 
  variety 
  of 
  form 
  and 
  composition 
  and 
  

   such 
  exceptionally 
  great 
  numbers. 
  

  

  A 
  most 
  interesting 
  group 
  is 
  that 
  of 
  the 
  Spanish 
  Peaks, 
  (station 
  121.) 
  

   Approaching 
  them 
  from 
  the 
  north, 
  the 
  two 
  mountains 
  are 
  seen 
  to 
  rise 
  

   far 
  above 
  the 
  level 
  of 
  the 
  surrounding 
  country, 
  and, 
  standing 
  isolated 
  

   as 
  they 
  do, 
  the 
  effect 
  of 
  their 
  height 
  is 
  still 
  increased. 
  The 
  fertile 
  val- 
  

   ley 
  of 
  the 
  Arapahoe 
  is 
  in 
  the 
  foreground, 
  and 
  from 
  it 
  rise 
  abruptly 
  the 
  

   forms 
  of 
  these 
  two 
  giants. 
  Innumerable 
  walls, 
  high 
  and 
  of 
  great 
  length, 
  

   stretch 
  from 
  the 
  valley 
  up 
  toward 
  the 
  summit 
  of 
  the 
  peaks, 
  while 
  soli- 
  

   tary 
  volcanic 
  buttes 
  give 
  evidence 
  of 
  others 
  that 
  have 
  crumbled 
  away. 
  

   On 
  the 
  west 
  side 
  of 
  the 
  mountains 
  narrow, 
  sharp 
  ridges, 
  surmounted 
  by 
  

  

  