﻿188 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  sliow 
  considerable 
  variation 
  of 
  color, 
  changing 
  from 
  the 
  subdued 
  yel- 
  

   low 
  and 
  grey 
  shades 
  to 
  reddish 
  orange 
  and 
  brown. 
  At 
  many 
  places 
  

   within 
  these 
  900 
  feet 
  of 
  shale 
  it 
  becomes 
  so 
  sandy 
  as 
  to 
  pass 
  for 
  a 
  very 
  

   argillaceous 
  sandstone. 
  Indistinct 
  remains 
  of 
  plants 
  are 
  found 
  there. 
  

   About 
  150 
  feet 
  of 
  sandstone 
  (Ii) 
  cover 
  the 
  shales. 
  There 
  is 
  here 
  no 
  evi- 
  

   dence 
  of 
  the 
  Puerco 
  marls, 
  unless, 
  indeed, 
  the 
  colors, 
  red 
  and 
  pink, 
  of 
  

   the 
  overlying 
  sandstone 
  (i) 
  should 
  furnish 
  an 
  indication 
  of 
  them. 
  With 
  

   this 
  latter 
  I 
  commence 
  the 
  Tertiary 
  series. 
  In 
  the 
  entire 
  region 
  under 
  

   discussion 
  shales, 
  marls, 
  and 
  sandstones 
  so 
  gradually 
  merge 
  into 
  each 
  

   other 
  that 
  the 
  local 
  absence 
  of 
  any 
  member, 
  that 
  is 
  elsewhere 
  found 
  in 
  

   the 
  same 
  horizon, 
  is 
  not 
  surprising. 
  More 
  particularly 
  in 
  the 
  horizontal 
  

   direction 
  does 
  this 
  change 
  take 
  place, 
  less 
  in 
  the 
  vertical. 
  Assuming 
  

   for 
  the 
  Dakota 
  group 
  a 
  thickness 
  of 
  about 
  1,200 
  feet, 
  we 
  find 
  the 
  entire 
  

   vertical 
  dimensions 
  of 
  the 
  Cretaceous 
  to 
  amount 
  to 
  about 
  4,500 
  feet 
  in 
  

   this 
  locality. 
  Within 
  short 
  distances, 
  even, 
  this 
  changes 
  considerably, 
  

   however. 
  One 
  or 
  the 
  other 
  series 
  of 
  shales 
  or 
  shales 
  and 
  sandstones 
  

   may 
  dwindle 
  down 
  to 
  comparatively 
  an 
  insignificant 
  thickness, 
  while 
  

   on 
  the 
  other 
  hand 
  it 
  may 
  be 
  increased. 
  

  

  About 
  eight 
  miles 
  west 
  of 
  station 
  42 
  the 
  old 
  trail 
  leaves 
  the 
  Nutria, 
  

   and 
  taking 
  a 
  more 
  direct 
  course, 
  crosses 
  the 
  Piedra 
  some 
  distance 
  above 
  

   the 
  junction 
  of 
  the 
  two 
  streams. 
  South 
  of 
  the 
  trail 
  we 
  find, 
  on 
  the 
  sum- 
  

   mit 
  of 
  a 
  prominent 
  hill, 
  an 
  isolated 
  column 
  of 
  sandstone 
  and 
  shales 
  

   (station 
  44). 
  To 
  explorers 
  this 
  landmark. 
  La 
  Piedra 
  Parada, 
  has 
  long 
  

   been 
  known.* 
  It 
  rises 
  as 
  a 
  column 
  to 
  a 
  height 
  of 
  over 
  400 
  feet, 
  and 
  is 
  

   made 
  still 
  more 
  conspicuous 
  by 
  the 
  position 
  it 
  occupies. 
  

  

  Southwest 
  of 
  the 
  Rio 
  San 
  Juan 
  the 
  Cretaceous 
  follows 
  the 
  base 
  of 
  the 
  

   Sawatch 
  Range. 
  By 
  the 
  numerous 
  streams 
  there, 
  the 
  once 
  connected 
  

   plateaus 
  are 
  cut 
  into 
  fragments. 
  Local 
  disturbances, 
  of 
  but 
  small 
  extent, 
  

   however, 
  have 
  produced 
  changes 
  in 
  the 
  general 
  southerly 
  dip. 
  They 
  

   have 
  been 
  mentioned 
  while 
  speaking 
  of 
  the 
  Colorado 
  group. 
  It 
  seems 
  

   possible 
  that 
  a 
  large 
  portion 
  of 
  this 
  former 
  plateau 
  was 
  at 
  one 
  time 
  cov- 
  

   ered 
  by 
  basalt. 
  Station 
  64 
  is 
  located 
  on 
  the 
  southern 
  edge 
  of 
  the 
  Cerro 
  

   del 
  Navajo, 
  the 
  entire 
  summit 
  of 
  which 
  is 
  covered 
  by 
  basalt. 
  At 
  that 
  

   point 
  the 
  elevation 
  is 
  9,115 
  feet, 
  while 
  on 
  the 
  same 
  horizon, 
  about 
  15 
  miles 
  

   farther 
  southwest, 
  it 
  is 
  9,019. 
  The 
  niveau, 
  in 
  that 
  direction, 
  has 
  under- 
  

   gone 
  but 
  slight 
  changes. 
  An 
  unbroken 
  bluff 
  is 
  presented 
  by 
  the 
  strata 
  

   of 
  the 
  Fox 
  Hills 
  on 
  the 
  western 
  side 
  of 
  the 
  Chama 
  Valley, 
  and 
  on 
  its 
  

   southwestern 
  slope, 
  in 
  the 
  valley, 
  we 
  find 
  a 
  lake 
  (Laguna 
  de 
  los 
  Cabal- 
  

   los) 
  very 
  nearly 
  on 
  the 
  continental 
  divide, 
  which 
  here 
  has 
  an 
  altitude 
  

   of 
  but 
  7,700 
  feet. 
  This 
  is 
  one 
  of 
  the 
  lowest, 
  if 
  not 
  the 
  lowest 
  conti- 
  

   nental 
  pass 
  in 
  the 
  UnitedStates. 
  

  

  To 
  the 
  north 
  and 
  northeast 
  of 
  the 
  bluff 
  mentioned, 
  there 
  are 
  several 
  

   remnants 
  of 
  the 
  ancient 
  plateau, 
  separated 
  from 
  each 
  other 
  by 
  the 
  out- 
  

   cropping, 
  underlying 
  Colorado 
  shales. 
  Station 
  63 
  is 
  one 
  of 
  the 
  highest 
  

   points 
  in 
  the 
  valley 
  there, 
  and 
  owes 
  its 
  present 
  altitude 
  to 
  a 
  protecting 
  

   cap 
  of 
  trachorheites 
  and 
  trachytic 
  conglomerate. 
  Ascending 
  it, 
  we 
  pass 
  

   through 
  westward-dipping 
  shales 
  of 
  the 
  Colorado 
  group, 
  then 
  reach 
  the 
  

   shales 
  and 
  sandstones 
  of 
  the 
  Fox 
  Hills, 
  and 
  finally 
  arrive 
  at 
  the 
  trachyte. 
  

   The 
  anticlinal 
  fold 
  described 
  as 
  occurring 
  in 
  the 
  valley 
  of 
  the 
  Navajo 
  

   extends 
  eastward 
  to 
  this 
  locality, 
  and 
  is 
  shown 
  by 
  a 
  slight 
  convex 
  curv- 
  

   ing 
  of 
  the 
  strata. 
  Barometric 
  measurement 
  determined 
  the 
  summit 
  of 
  

   the 
  mountain 
  to 
  reach 
  an 
  altitude 
  of 
  9,905 
  feet. 
  Could 
  we 
  assume 
  a 
  per- 
  

   fect 
  connection 
  of 
  all 
  the 
  scattered 
  outcrops, 
  which 
  connection 
  existed 
  

   at 
  the 
  time 
  the 
  Tertiary 
  beds 
  were 
  deposited 
  and 
  the 
  later 
  volcanic 
  rocks 
  

  

  * 
  Compare 
  Report 
  Exploring 
  Expedition 
  J. 
  N. 
  Macomb, 
  1859, 
  1876, 
  p. 
  78. 
  

  

  