﻿PEALE] 
  ARCH^AN 
  ROCKS 
  UNCOMPAHGRE 
  PLATEAU. 
  67 
  

  

  pebble-like 
  form 
  and 
  might 
  once 
  have 
  been 
  bowlders, 
  which 
  would 
  indi- 
  

   cate 
  that 
  they 
  are 
  metamorphics 
  of 
  conglomerates. 
  The 
  red 
  beds 
  rest 
  

   immediately 
  on 
  these 
  rocks, 
  i3ut 
  are 
  thicker 
  at 
  station 
  38 
  than 
  at 
  station 
  

   IN"o. 
  40. 
  They 
  have 
  a 
  sloping, 
  terrace-like 
  edge 
  to 
  the 
  granite, 
  which 
  

   forms 
  a 
  bench 
  on 
  both 
  sides 
  of 
  the 
  caiion, 
  the 
  level 
  not 
  varying 
  mate- 
  

   rially 
  on 
  one 
  side 
  from 
  that 
  on 
  the 
  other. 
  The 
  cliffs 
  are 
  precipitous 
  for 
  

   nearly 
  two-thirds 
  of 
  their 
  height. 
  The 
  other 
  third 
  is 
  a 
  slope 
  to 
  the 
  center 
  

   of 
  the 
  valley 
  caused 
  by 
  the 
  weathering 
  of 
  the 
  cliffs. 
  In 
  many 
  places 
  

   the 
  cliffs 
  present 
  solid 
  perpendicular 
  faces, 
  while 
  at 
  others 
  they 
  are 
  

   broken 
  into 
  pinnacles 
  and 
  needle-like 
  projections. 
  

  

  The 
  divide 
  between 
  the 
  two 
  creeks 
  is 
  nearly 
  two 
  miles 
  in 
  length 
  from 
  

   the 
  Gunnison 
  branch 
  (East 
  Creek) 
  to 
  the 
  Dolores 
  branch, 
  (West 
  Creek,) 
  

   and 
  increases 
  in 
  width 
  from 
  half 
  a 
  mile 
  on 
  the 
  east 
  side, 
  to 
  a 
  mile 
  at 
  the 
  

   head 
  of 
  the 
  Western 
  Creek. 
  The 
  general 
  level 
  is 
  very 
  nearly 
  preserved, 
  

   being 
  about 
  7,036 
  feet 
  above 
  sea-level. 
  

  

  At 
  station 
  34 
  the 
  granite 
  walls 
  are 
  about 
  fifteen 
  hundred 
  feet 
  high 
  

   and 
  at 
  station 
  39 
  they 
  have 
  increased 
  to 
  1,917 
  feet. 
  West 
  Creek 
  now 
  

   begins 
  to 
  descend 
  more 
  rapidly, 
  while 
  the 
  top 
  of 
  the 
  granite 
  still 
  inclines 
  

   at 
  about 
  the 
  same 
  angle 
  to 
  the 
  eastward. 
  This 
  would 
  give 
  us, 
  farther 
  

   down 
  the 
  caiion, 
  a 
  wall 
  of 
  granite 
  nearly 
  three 
  thousand 
  feet 
  high. 
  

  

  In 
  all 
  this 
  length 
  of 
  the 
  canon 
  we 
  find 
  only 
  red 
  sandstones 
  (Triassic) 
  

   resting 
  on 
  the 
  gneissic 
  rocks. 
  They 
  gradually 
  increase 
  in 
  thickness 
  as 
  

   we 
  go 
  westward 
  and 
  end 
  abruptly 
  on 
  the 
  edge 
  of 
  the 
  caiion 
  and 
  also 
  

   along 
  the 
  crest 
  of 
  the 
  plateau. 
  When 
  we 
  emerge 
  from 
  the 
  more 
  rugged 
  

   part 
  of 
  the 
  caiion 
  to 
  the 
  comparatively 
  open 
  valley, 
  extending 
  from 
  the 
  

   Dolores 
  some 
  four 
  or 
  five 
  miles 
  up 
  the 
  creek, 
  we 
  find 
  older 
  beds, 
  with 
  

   the 
  ends 
  tipped 
  up 
  against 
  the 
  coarse 
  granitic 
  rocks. 
  The 
  overlying 
  red 
  

   beds 
  have 
  been 
  removed 
  at 
  the 
  junction. 
  The 
  prevailing 
  character 
  of 
  

   the 
  rocks 
  of 
  the 
  Archaean 
  portion 
  of 
  the 
  Unaweep 
  caiion 
  are 
  coarse 
  

   granitic 
  and 
  gneissic 
  beds 
  intersected 
  with 
  seams 
  of 
  quartz 
  and 
  feldspar, 
  

   but 
  as 
  far 
  as 
  observed 
  without 
  the 
  stratification 
  observed 
  in 
  the 
  exposures 
  

   farther 
  north. 
  Whether 
  they 
  are 
  of 
  the 
  same 
  age 
  it 
  is 
  impossible 
  to 
  say, 
  

   although 
  it 
  seems 
  probable 
  that 
  they 
  are 
  older. 
  Without 
  any 
  chance 
  to 
  

   trace 
  the 
  connection 
  between 
  the 
  two 
  exposures, 
  all 
  opinions 
  as 
  to 
  their 
  

   relative 
  age 
  must 
  be 
  merely 
  conjectural. 
  

  

  Along 
  the 
  western 
  edge 
  of 
  the 
  plateau 
  we 
  find 
  three 
  areas 
  in 
  which 
  

   Archaean 
  rocks 
  are 
  exposed. 
  These 
  will 
  be 
  more 
  readily 
  understood 
  by 
  

   reference 
  to 
  the 
  general 
  geological 
  map, 
  when 
  published. 
  The 
  first 
  is 
  

   west 
  of 
  station 
  35, 
  and 
  is 
  connected 
  with 
  the 
  Archaean 
  area 
  of 
  Unaweep 
  

   Canon 
  by 
  a 
  narrow 
  strip. 
  The 
  other 
  two 
  are 
  farther 
  south, 
  and 
  are 
  iso- 
  

   lated 
  one 
  from 
  the 
  other, 
  the 
  space 
  between 
  being 
  covered 
  by 
  Triassic 
  

   and 
  fragments 
  of 
  Jurassic 
  strata. 
  

  

  It 
  is 
  only 
  where 
  the 
  continuity 
  of 
  the 
  beds 
  forming 
  the 
  monoclinal 
  

   fold 
  has 
  been 
  broken 
  and 
  the 
  rocks 
  removed 
  that 
  Archaean 
  rocks 
  are 
  

   seen. 
  This 
  we 
  find 
  to 
  be 
  generally 
  the 
  case 
  where 
  the 
  folding 
  was 
  ac- 
  

   companied 
  by 
  faulting. 
  As 
  we 
  go 
  south, 
  the 
  erosion 
  subsequent 
  to 
  the 
  

   folding 
  has 
  removed 
  only 
  a 
  portion 
  of 
  the 
  beds, 
  and 
  the 
  Archaean 
  rocks 
  

   do 
  not 
  show 
  even 
  where 
  the 
  streams 
  cut 
  across 
  the 
  fold. 
  

  

  Near 
  station 
  27 
  the 
  rock 
  is 
  a 
  coarse 
  reddish 
  granitic 
  rock, 
  in 
  which- 
  1 
  

   could 
  find 
  no 
  traces 
  of 
  stratification 
  in 
  the 
  limited 
  exposure. 
  

  

  As 
  we 
  have 
  already 
  said, 
  the 
  rocks 
  which 
  we 
  have 
  been 
  considering 
  

   in 
  this 
  chapter 
  probably 
  underlie 
  the 
  entire 
  district. 
  They 
  are 
  meta- 
  

   morphic, 
  and 
  it 
  is 
  doubtful 
  if 
  any 
  true 
  igneous 
  granitic 
  rocks 
  would 
  be 
  

   seen 
  among 
  them 
  if 
  we 
  could 
  have 
  the 
  later 
  sedimentary 
  coverings 
  re- 
  

   moved. 
  

  

  They 
  were 
  once 
  deposited 
  as 
  sediments. 
  Whence 
  were 
  their 
  materials 
  

  

  