﻿154 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  sumption 
  that 
  the 
  general 
  configuration 
  of 
  country 
  was 
  already 
  a 
  varied 
  

   one 
  at 
  the 
  time 
  of 
  the 
  trachytic 
  eruptions. 
  In 
  1874 
  an 
  analogous 
  case 
  

   was 
  observed 
  at 
  the 
  head 
  Cunningham 
  Gulch, 
  where 
  limestones, 
  

   probably 
  of 
  Devonian 
  age, 
  occurred 
  in 
  a 
  single 
  outcrop, 
  overlying 
  

   metamorphic 
  schists, 
  covered 
  by 
  trachyte 
  No. 
  4. 
  No 
  fossils 
  were 
  found 
  

   on 
  station 
  56 
  of 
  1874; 
  but 
  the 
  characteristic 
  chalcedonic 
  concretions 
  

   occurred 
  that 
  indicate 
  locally 
  the 
  age 
  of 
  the 
  stratum. 
  At 
  the 
  eastern 
  

   end 
  of 
  the 
  great 
  Horseshoe 
  Bend 
  in 
  the 
  Rio 
  Grande 
  is 
  Wagon-wheel 
  

   Gap, 
  generally 
  only 
  called 
  the 
  Gap. 
  This 
  is 
  a 
  vertical 
  rent 
  in 
  the 
  

   trachyte, 
  that 
  there 
  formed 
  a 
  narrow 
  ridge, 
  running 
  north 
  and 
  south. 
  

   Formerly, 
  before 
  this 
  passage 
  was 
  effected, 
  the 
  river 
  flowed 
  around 
  

   the 
  place, 
  making 
  a 
  curve 
  to 
  the 
  southward, 
  and 
  probably 
  formed 
  

   a 
  lake 
  west 
  of 
  it. 
  Vertical 
  walls, 
  about 
  800 
  feet 
  in 
  height, 
  now 
  inclose 
  

   the 
  Rio 
  Grande, 
  which 
  so 
  nearly 
  fills 
  the 
  gap 
  produced, 
  that 
  room 
  ia 
  

   left 
  on 
  either 
  side 
  of 
  it 
  only 
  for 
  a 
  wagon-road. 
  The 
  north 
  wall 
  is 
  the 
  

   higher 
  one 
  of 
  the 
  two, 
  measuring 
  about 
  1,200 
  feet. 
  From 
  there 
  the 
  

   mountain 
  or 
  former 
  ridge 
  slopes 
  upward, 
  until 
  it 
  culminates 
  in 
  the 
  

   summit 
  upon 
  which 
  station 
  25 
  was 
  located, 
  at 
  an 
  elevation 
  of 
  10,279 
  

   feet, 
  2,000 
  feet 
  above 
  the 
  river. 
  The 
  trachyte 
  here 
  belongs 
  to 
  No. 
  2 
  

   upper, 
  and 
  shows 
  on 
  either 
  side 
  columnar 
  structure, 
  which 
  no 
  doubt 
  

   facilitated 
  the 
  rupture, 
  that 
  cannot 
  otherwise 
  have 
  been 
  formed 
  

   than 
  by 
  violent 
  demonstration 
  of 
  force. 
  Whether 
  this 
  force 
  was 
  

   seismic, 
  however, 
  or 
  whether 
  more 
  gradually-acting 
  agents 
  were 
  em- 
  

   I)loyed, 
  I 
  am 
  unable 
  to 
  decide. 
  Indians 
  utilized 
  the 
  southern 
  hill 
  as 
  a 
  

   point 
  of 
  ''lookout." 
  A 
  long, 
  low 
  wall 
  runs 
  along 
  its 
  entire 
  northern 
  

   edge, 
  and 
  round 
  towers, 
  two 
  to 
  five 
  feet 
  high, 
  are 
  placed 
  along 
  it 
  at 
  

   different 
  intervals. 
  Walls 
  on 
  the 
  south 
  afforded 
  protection 
  against 
  any 
  

   one 
  advancing 
  up 
  the 
  gentle 
  slope 
  from 
  that 
  direction. 
  

  

  The 
  fortifications 
  are 
  well 
  conceived, 
  and 
  the 
  locality 
  chosen 
  with 
  

   judgment. 
  Numerous 
  fragments 
  of 
  chalcedony 
  and 
  jasper, 
  occurring 
  in 
  

   the 
  trachyte 
  of 
  No. 
  2, 
  furnished 
  material 
  for 
  the 
  manufacture 
  of 
  arrow 
  

   and 
  spear 
  heads, 
  a 
  number 
  of 
  which 
  were 
  found 
  in 
  the 
  old 
  stronghold. 
  

   Mr. 
  Wilson 
  found 
  one 
  arrow-head 
  of 
  obsidian, 
  which 
  certainly 
  was 
  never 
  

   obtained 
  from 
  any 
  locality 
  in 
  Colorado, 
  but 
  must 
  have 
  come 
  from 
  New 
  

   Mexico, 
  or 
  even 
  farther 
  south. 
  Joining 
  the 
  Rio 
  Grande, 
  immediately 
  

   below 
  the 
  gap 
  is 
  Hot 
  Springs 
  Creek, 
  which 
  heads 
  on 
  the 
  northeast 
  side 
  

   of 
  station 
  28. 
  This 
  name 
  has 
  been 
  given 
  to 
  the 
  stream 
  from 
  the 
  occur- 
  

   rence 
  of 
  several 
  hot 
  springs 
  there, 
  within 
  a 
  mile 
  of 
  its 
  junction 
  with 
  the 
  

   river. 
  Three 
  springs 
  are 
  there, 
  all 
  situated 
  but 
  a 
  short 
  distance 
  from 
  the 
  

   creek, 
  one 
  on 
  the 
  west, 
  two 
  on 
  the 
  east 
  side. 
  One 
  of 
  them, 
  the 
  largest, 
  has 
  

   been 
  led 
  into 
  a 
  bathing-house, 
  and 
  the 
  water 
  there 
  shows 
  a 
  temperature 
  

   of 
  105° 
  F. 
  The 
  observations 
  as 
  to 
  temperature 
  were 
  made 
  July 
  4, 
  1875, 
  

   7 
  p. 
  m. 
  A 
  short 
  distance 
  above 
  the 
  house 
  is 
  the 
  spring 
  itself. 
  It 
  is 
  

   contained 
  in 
  a 
  natural 
  basin, 
  oval 
  in 
  shape, 
  measuring 
  11 
  feet 
  by 
  7, 
  along 
  

   its 
  two 
  axes. 
  Here 
  the 
  temperature 
  of 
  the 
  water 
  is 
  131° 
  F. 
  Bubbling 
  up 
  

   from 
  the 
  center, 
  carbonic-acid 
  gas 
  and 
  sulphureted 
  hydrogen 
  escape 
  in 
  

   great 
  volume, 
  while 
  the 
  mineral 
  constituents, 
  carbonates 
  of 
  lime, 
  soda, 
  

   and 
  potash, 
  are 
  either 
  deposited 
  on 
  the 
  bottom, 
  or 
  aid 
  in 
  building 
  up 
  the 
  

   rim 
  of 
  the 
  basin 
  that 
  confines 
  the 
  spring. 
  Some 
  iron 
  is 
  also 
  in 
  solution. 
  

   At 
  the 
  base 
  of 
  a 
  low 
  bluff' 
  the 
  upper 
  spring 
  issues, 
  showing 
  a 
  temperature 
  of 
  

   122° 
  F. 
  and 
  containing 
  the 
  same 
  minerals 
  in 
  solution. 
  Its 
  clear 
  water 
  in- 
  

   vites 
  to 
  tasting, 
  but 
  the 
  alkalinity 
  it 
  possesses 
  in 
  a 
  high 
  degree 
  soon 
  de- 
  

   stroys 
  its 
  application 
  as 
  a 
  continual 
  beverage. 
  The 
  third 
  spring, 
  between 
  

   the 
  two, 
  measured 
  107° 
  F. 
  It 
  is 
  surrounded 
  by 
  a 
  considerable 
  deposit 
  of 
  

   carbonate 
  and 
  bicarbonate 
  of 
  soda, 
  and 
  the 
  taste 
  of 
  the 
  water 
  is 
  that 
  of 
  

   a 
  nearly 
  saturated 
  solution. 
  These 
  springs 
  have 
  attained 
  a 
  local 
  repu- 
  

  

  