﻿116 
  EEPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  limestone 
  (h). 
  Under 
  tbeye 
  is 
  a 
  series 
  of 
  red 
  sandstone 
  strata. 
  Very 
  

   near 
  the 
  junction 
  of 
  the 
  two, 
  in 
  the 
  limestone, 
  numerous 
  specimens 
  of 
  

   Productus 
  scmiretieulatus 
  were 
  found 
  in 
  pooitu. 
  After 
  the 
  sandstones 
  

   nnderlyiug 
  follow 
  tw^o 
  beds 
  of 
  limestone 
  (c), 
  separated 
  by 
  another 
  sand- 
  

   stoue 
  [d). 
  Immediately 
  under 
  the 
  second 
  limestone-bed, 
  so 
  far 
  as 
  could 
  

   be 
  observed, 
  occurs 
  the 
  whitish 
  trachyte 
  (e) 
  above 
  mentioned. 
  It 
  seems 
  

   probable 
  that 
  the 
  eruption 
  of 
  this 
  trachyte 
  caused 
  the 
  formation 
  of 
  the 
  

   aoticlinal 
  fold 
  that 
  can 
  be 
  observed, 
  unless, 
  indeed, 
  the 
  fold 
  was 
  created 
  

   by 
  other 
  causes 
  and 
  the 
  volcanic 
  material 
  merely 
  took 
  advantage 
  there- 
  

   of 
  to 
  occup}' 
  its 
  present 
  position. 
  Having 
  passed 
  the 
  trachyte, 
  we 
  find 
  

   a 
  repetition 
  only 
  in 
  reversed 
  order 
  of 
  the 
  last 
  named 
  strata, 
  dipping, 
  

   this 
  time, 
  in 
  conformity 
  with 
  the 
  anticlinal 
  fold 
  in 
  a 
  westerly 
  direction 
  at 
  

   an 
  angle 
  of 
  about 
  20°. 
  The 
  sandstone 
  strata 
  (/), 
  however, 
  corresponding 
  

   to 
  h 
  here 
  suddenly 
  curve 
  upward 
  and 
  form 
  a 
  synclinal 
  fold 
  of 
  small 
  dimen- 
  

   sions. 
  It 
  is 
  tobe 
  assumed 
  thatthis 
  pointis 
  very 
  nearthe 
  original 
  central 
  

   line 
  of 
  the 
  folding; 
  therefore 
  the 
  strata 
  corresponding 
  to 
  each 
  other 
  are 
  

   but 
  a 
  very 
  short 
  horizontal 
  distance 
  apart. 
  Sandstones 
  form 
  the 
  center 
  

   of 
  the 
  «fold, 
  while 
  dark-red 
  argillaceous 
  shales 
  adjoin 
  them 
  on 
  the 
  out- 
  

   side. 
  In 
  these 
  shales 
  specimens 
  of 
  Bigillaria 
  were 
  observed 
  ; 
  they 
  are 
  

   pressed 
  very 
  fiat, 
  and 
  owing 
  to 
  the 
  nature 
  of 
  the 
  rock 
  they 
  are 
  found 
  in, 
  

   but 
  poorly 
  preserved. 
  Instead 
  of 
  the 
  strata 
  now 
  continuing 
  the 
  easterly 
  

   dip 
  they 
  have 
  gained 
  through 
  the 
  synclinal 
  fold 
  , 
  they 
  turn 
  to 
  the 
  west 
  again 
  

   as 
  soon 
  as 
  the 
  limestone 
  series 
  {g) 
  is 
  reached. 
  This 
  is 
  of 
  considerable 
  

   thickness, 
  analogous 
  to 
  that 
  near 
  the 
  head 
  of 
  the 
  jDass. 
  Three 
  beds 
  of 
  

   sandstone 
  then 
  set 
  in 
  (/i), 
  dipping 
  westward 
  at 
  an 
  angle 
  of 
  about 
  30°, 
  

   and 
  separated 
  by 
  two 
  beds 
  of 
  limestone 
  {%). 
  Immediately 
  after 
  the 
  last 
  

   bed 
  of 
  sandstone 
  we 
  come 
  upon 
  metamorphic 
  granite 
  (/c), 
  which 
  proba- 
  

   bly 
  during 
  the 
  Carboniferous 
  period 
  served 
  as 
  a 
  shore 
  for 
  the 
  rocks 
  that 
  

   now 
  rest 
  against 
  it. 
  It 
  seems 
  likely 
  that 
  this 
  granite, 
  too, 
  has 
  been 
  

   disturbed 
  from 
  its 
  original 
  position, 
  inasmuch 
  as 
  otherwise 
  the 
  deposi- 
  

   tion 
  of 
  sedimentary 
  beds 
  could 
  scarcely 
  have 
  occurred 
  in 
  the 
  way 
  it 
  

   is 
  now 
  observed. 
  Trachyte 
  (/), 
  u])on 
  which 
  station 
  7 
  is 
  located, 
  covers 
  

   the 
  granite 
  and 
  is 
  followed 
  by 
  drift 
  [m). 
  

  

  Making 
  an 
  attempt 
  to 
  reduce 
  the 
  plications 
  here 
  observed 
  with 
  many 
  

   interruptions 
  to 
  one 
  single 
  fold, 
  the 
  identity 
  of 
  strata 
  has 
  to 
  be 
  consid- 
  

   ered. 
  Could 
  more 
  time 
  have 
  been 
  spared, 
  more 
  thorough 
  results 
  as 
  re- 
  

   gards 
  detail 
  might 
  have 
  been 
  obtained. 
  The 
  section 
  was 
  made 
  as 
  care- 
  

   fully 
  as 
  may 
  be 
  possible 
  without 
  accurate 
  horizontal 
  measurements 
  and 
  

   the 
  subsequent 
  calculation 
  of 
  thickness 
  of 
  strata. 
  On 
  either 
  side 
  of 
  the 
  

   trachyte 
  the 
  strata 
  are 
  the 
  same; 
  it 
  is 
  a 
  simple 
  anticlinal 
  fold, 
  followed 
  

   farther 
  west 
  by 
  a 
  synclinal 
  one 
  of 
  small 
  dimensions. 
  Beyond 
  this, 
  how- 
  

   ever, 
  we 
  are 
  somewhat 
  at 
  a 
  loss 
  how 
  to 
  place 
  the 
  heavy 
  beds 
  of 
  lime- 
  

   stone. 
  So 
  far 
  as 
  could 
  be 
  determined 
  they 
  are 
  the 
  same 
  as 
  the 
  more 
  

   easterly 
  ones, 
  but 
  appear 
  to 
  be 
  totally 
  detached 
  from 
  them, 
  and 
  thrown 
  

   into 
  their 
  present 
  abnormal 
  position. 
  This, 
  too, 
  accounts 
  for 
  the 
  pecu- 
  

   liar 
  relative 
  position 
  of 
  the 
  granite 
  and 
  the 
  sedimentary 
  beds 
  to 
  a 
  certain 
  

   extent. 
  

  

  South 
  of 
  Sangre 
  de 
  Cristo 
  Pass 
  is 
  the 
  Indian 
  Creek 
  Pass. 
  It 
  is 
  but 
  

   little 
  used, 
  although 
  a 
  wagon-road 
  leads 
  up 
  to 
  it. 
  Here, 
  again, 
  on 
  the 
  

   north 
  side 
  of 
  the 
  road, 
  is 
  a 
  good 
  exj^osure 
  of 
  the 
  rocks. 
  Ascending 
  from 
  

   San 
  Luis 
  Valley, 
  trachyte 
  is 
  first 
  encountered, 
  then 
  metamorphic 
  gran- 
  

   ite; 
  joining 
  on 
  to 
  this 
  the 
  sedimentaries 
  begin. 
  So 
  far 
  as 
  could 
  be 
  judged, 
  

   the 
  junction 
  is 
  an 
  abrupt 
  one, 
  the 
  sandstone 
  leaning 
  against 
  the 
  gran- 
  

   ite 
  with 
  a 
  very 
  steep 
  easterly 
  dip. 
  A 
  continuous 
  easterly 
  dip 
  may 
  be 
  

   observed 
  throughout 
  the 
  succeeding 
  strata, 
  which 
  consist 
  of 
  limestones 
  

   and 
  sandstones 
  alternating. 
  An 
  abrupt 
  stop 
  of 
  the 
  strata 
  occurs 
  a 
  short 
  

  

  