﻿HOLMES.] 
  UPPER 
  CRETACEOUS 
  AND 
  TERTIARY 
  FORMATIONS. 
  249 
  

  

  era! 
  westerly 
  directiou. 
  In 
  its 
  middle 
  course 
  it 
  bends 
  south 
  into 
  New 
  

   Mexico, 
  but 
  soon 
  enters 
  Colorado 
  again 
  at 
  the 
  extreme 
  southwest 
  corner, 
  

   and 
  thence 
  crosses 
  into 
  Southeastern 
  Utah. 
  The 
  area 
  drained 
  by 
  it 
  

   will 
  probably 
  not 
  fall 
  short 
  of 
  20,000 
  square 
  miles. 
  This 
  area 
  is 
  divided 
  

   between 
  four 
  Territories, 
  and 
  consists 
  mostly 
  of 
  the 
  dry 
  plain 
  country 
  

   of 
  the 
  eastern 
  border 
  of 
  the 
  Colorado 
  Plateau. 
  On 
  the 
  north 
  are 
  five 
  

   important 
  tributaries, 
  all 
  of 
  which 
  have 
  their 
  sources 
  in 
  the 
  high 
  mount- 
  

   ain 
  region 
  to 
  the 
  north. 
  Of 
  these 
  the 
  Animas 
  is 
  the 
  largest, 
  being 
  at 
  

   its 
  junction 
  with 
  the 
  San 
  Juan 
  fully 
  two-thirds 
  as 
  great 
  as 
  that 
  stream. 
  

   For 
  soDie 
  distance 
  above 
  the 
  junction 
  both 
  streams 
  are 
  in 
  canons, 
  

   formed 
  of 
  Upper 
  Cretaceous 
  and 
  Tertiary 
  rocks, 
  but 
  at 
  the 
  crossing 
  of 
  

   meridian 
  108° 
  they 
  enter 
  wide 
  terraced 
  valleys, 
  bordered 
  by 
  low 
  bluffs. 
  

   These 
  bluffs 
  ^re 
  composed 
  of 
  the 
  sandstones 
  of 
  the 
  Pinou 
  Mesa 
  Group 
  

   and 
  outcrops 
  of 
  the 
  Bad 
  Land 
  marls 
  occur 
  in 
  the 
  slopes. 
  The 
  imme- 
  

   diate 
  borders 
  of 
  the 
  stream 
  are 
  rendered 
  very 
  attractive 
  and 
  beauti- 
  

   ful 
  by 
  the 
  growth 
  of 
  cottonwood 
  trees 
  which 
  line 
  the 
  banks, 
  and 
  fre- 
  

   quently 
  extend 
  back 
  over 
  the 
  river 
  bottoms. 
  On 
  the 
  borders 
  of 
  these 
  

   groves 
  are 
  dense 
  growths 
  of 
  bushes 
  and 
  broad 
  meadows 
  of 
  fine 
  grass. 
  

   Throughout 
  its 
  entire 
  lower 
  course 
  the 
  river 
  is 
  marked 
  by 
  these 
  verdant 
  

   borders. 
  In 
  the 
  upper 
  and 
  middle 
  course 
  it 
  is 
  clear 
  and 
  sparkling 
  for 
  

   many 
  months 
  of 
  the 
  year, 
  but 
  farther 
  down 
  passes 
  through 
  wide 
  belts 
  

   of 
  friable 
  rock, 
  and 
  becomes 
  clogged 
  with 
  sediment, 
  and 
  abounds 
  in 
  

   treacherous 
  quicksands. 
  

  

  Station 
  9 
  was 
  made 
  on 
  the 
  higher 
  of 
  two 
  small 
  buttes 
  that 
  lie 
  be- 
  

   tween 
  the 
  La 
  Plata 
  and 
  Animas, 
  and 
  about 
  6 
  miles 
  from 
  the 
  junction 
  

   of 
  the 
  former 
  with 
  the 
  San 
  Juan. 
  The 
  strata 
  forming 
  these 
  buttes 
  are 
  

   the 
  yellow 
  sandstones 
  of 
  the 
  Piiion 
  Mesa 
  Group. 
  At 
  the 
  base 
  is 
  the 
  

   heavy 
  stratum 
  of 
  sandstone 
  that 
  forms 
  the 
  escarpment 
  of 
  the 
  Piiion 
  

   Mesa 
  on 
  the 
  west, 
  and 
  which 
  immediately 
  overlies 
  the 
  Bad 
  Land 
  Group. 
  

   This 
  sandstone 
  stratum 
  is 
  at 
  the 
  base 
  of 
  a 
  very 
  extensive 
  series 
  of 
  sand- 
  

   stones, 
  which 
  have 
  alternating 
  bands 
  of 
  gray, 
  greenish, 
  and 
  pinkish 
  

   marls. 
  These 
  sandstones, 
  as 
  I 
  afterwards 
  found, 
  in 
  passing 
  up 
  the 
  San 
  

   Juan, 
  reach 
  a 
  thickness 
  of 
  some 
  1,500 
  feet, 
  being 
  always 
  massive, 
  whitish, 
  

   and 
  yellowish, 
  frequently 
  coarse, 
  almost 
  a 
  conglomerate 
  and 
  slightly 
  

   compacted, 
  while 
  the 
  marls, 
  although 
  unimportant 
  as 
  to 
  thickness, 
  alter- 
  

   nate 
  very 
  regularly 
  at 
  intervals 
  of 
  from 
  5 
  to 
  25 
  feet, 
  giving 
  in 
  the 
  

   weathering 
  of 
  the 
  high 
  cliffs 
  a 
  heavy 
  laminated 
  appearance. 
  The 
  form- 
  

   ation 
  does 
  not 
  seem 
  favorable 
  for 
  the 
  preservation 
  of 
  fossils, 
  and 
  I 
  was 
  

   unable 
  to 
  find 
  anything 
  that 
  could 
  be 
  identified. 
  It 
  seems, 
  however, 
  to 
  

   correspond 
  to 
  the 
  Lower 
  Eocene 
  sandstone 
  of 
  the 
  Nacemiento 
  Mountain 
  

   region 
  described 
  by 
  Cope 
  in 
  the 
  Report 
  of 
  the 
  Chief 
  of 
  Engineers 
  for 
  

   1875. 
  Its 
  stratigraphical 
  relations 
  appear 
  to 
  be 
  the 
  same 
  as 
  those 
  of 
  the 
  

   Wahsatch 
  Group 
  as 
  it 
  occurs 
  in 
  the 
  valleys 
  of 
  the 
  Grand 
  and 
  Green 
  

   Rivers. 
  

  

  The 
  little 
  butte 
  on 
  which 
  Station 
  9 
  was 
  made, 
  as 
  well 
  as 
  two 
  or 
  three 
  

   others 
  of 
  corresponding 
  height 
  in 
  the 
  vicinity, 
  seem 
  to 
  be 
  the 
  remnants 
  

   of 
  a 
  former 
  terrace, 
  as 
  the 
  tops 
  are 
  leveled 
  off" 
  and 
  covered 
  with 
  a 
  heavy 
  

   bed 
  of 
  drift 
  ; 
  bowlders 
  of 
  the 
  harder 
  crystalline 
  rocks 
  occur 
  a 
  foot 
  or 
  more 
  

   in 
  diameter. 
  The 
  height 
  above 
  the 
  present 
  river-level 
  is 
  by 
  baromet- 
  

   rical 
  measurement 
  upwards 
  of 
  900 
  feet. 
  Station 
  11, 
  some 
  10 
  miles 
  

   farther 
  down 
  the 
  valley, 
  was 
  made 
  on 
  a 
  butte 
  of 
  slightly 
  inferior 
  height, 
  

   which 
  was 
  also 
  covered 
  with 
  quantities 
  of 
  similar 
  drift. 
  The 
  lower 
  

   terrace- 
  levels 
  are 
  more 
  distinctly 
  marked, 
  and 
  cover 
  a 
  great 
  number 
  of 
  

   square 
  miles 
  in 
  this 
  part 
  of 
  the 
  valley. 
  Generally 
  they 
  seem 
  to 
  have 
  but 
  

   little 
  drift 
  deposit, 
  and 
  are 
  simply 
  the 
  soft 
  sandstones 
  and 
  marls 
  leveled 
  

   to 
  asuccessioji 
  of 
  flood-plains. 
  Occasionally^ 
  large 
  bowlders 
  occur, 
  and 
  

  

  