﻿HOLMES.] 
  MIDDLE 
  AND 
  LOWER 
  CRETACEOUS 
  FORMATIONS. 
  259 
  

  

  level, 
  and 
  pretty 
  full 
  outcrops 
  of 
  the 
  same 
  limestone 
  and 
  the 
  black 
  

   shales 
  beneath 
  may 
  be 
  seen 
  in 
  the 
  steep 
  banks 
  of 
  the 
  river. 
  Along 
  

   the 
  trail 
  between 
  Parrott 
  on 
  the 
  Mancos 
  the 
  shales 
  appear 
  on 
  all 
  hands, 
  

   and 
  in 
  many 
  places 
  extend 
  high 
  up 
  the 
  mountain-slopes. 
  The 
  Dakota 
  

   sandstones 
  are 
  exposed 
  where 
  erosion 
  has 
  been 
  deepest. 
  On 
  the 
  west- 
  

   ern 
  faces 
  of 
  the 
  La 
  Plata 
  Mountains 
  the 
  shales 
  are 
  found 
  high 
  up, 
  and 
  

   are 
  in 
  many 
  cases 
  interbedded 
  with 
  the 
  trachyte 
  of 
  the 
  summits. 
  The 
  

   Mancos 
  River 
  above 
  Merritt's 
  ranch 
  has 
  cut 
  down 
  through 
  the 
  shales 
  

   and 
  exposed 
  200 
  to 
  300 
  feet 
  of 
  the 
  Dakota 
  sandstones. 
  Between 
  the 
  

   Mancos 
  and 
  Lost 
  Caiion 
  the 
  formations 
  sink 
  again 
  almost 
  to 
  the 
  hori- 
  

   zontal, 
  and 
  the 
  shales 
  have 
  nearly 
  all 
  been 
  carried 
  off, 
  leaving 
  a 
  smooth 
  

   floor 
  of 
  the 
  Dakota 
  sandstones. 
  The 
  same 
  may 
  be 
  said 
  of 
  the 
  extensive 
  

   sloping 
  plain 
  that 
  extends 
  far 
  out 
  to 
  the 
  west 
  between 
  the 
  McElmo 
  and 
  

   Dolores 
  Elvers. 
  Patches 
  of 
  the 
  shales 
  remain 
  in 
  the 
  more 
  protected 
  

   localities, 
  and 
  frequently 
  where 
  the 
  shales 
  have 
  been 
  entirely 
  removed, 
  

   quantities 
  of 
  Gryphea 
  and 
  Oyster 
  shells 
  lie 
  about 
  on 
  the 
  hard 
  sandstone 
  

   floor. 
  North 
  of 
  the 
  Dolores, 
  on 
  the 
  high 
  plateau 
  regions 
  which 
  separate 
  

   that 
  river 
  from 
  the 
  Eio 
  San 
  Miguel, 
  large 
  areas 
  of 
  the 
  Middle 
  Cretaceous 
  

   formations 
  remain. 
  In 
  the 
  small 
  mesas 
  west 
  of 
  Lone 
  Cone 
  the 
  entire 
  

   series 
  of 
  shales 
  has 
  been 
  preserved, 
  the 
  caps 
  of 
  the 
  mesas 
  being 
  of 
  the 
  

   Mesa 
  Verde 
  sandstones. 
  Lower 
  Esoarpment 
  group. 
  In 
  the 
  San 
  Miguel 
  

   Mountains 
  the 
  shales 
  have 
  been 
  preserved 
  by 
  the 
  flows 
  of 
  trachyte, 
  

   with 
  which 
  they 
  are 
  now 
  interbedded. 
  

  

  LOWER 
  CRETACEOUS 
  FORMATIONS. 
  

  

  The 
  group 
  of 
  sandstones 
  that 
  immediately 
  underlies 
  the 
  shales 
  is, 
  ap- 
  

   parently, 
  in 
  the 
  southwest 
  the 
  most 
  important 
  members 
  of 
  the 
  Cretaceous 
  

   formations. 
  Although 
  it 
  does 
  not 
  comprise 
  as 
  great 
  a 
  thickness 
  of 
  strata 
  

   as 
  either 
  of 
  the 
  other 
  grand 
  divisions, 
  the 
  superior 
  compactness 
  of 
  the 
  rocks 
  

   "has 
  been 
  the 
  means 
  of 
  retarding 
  and 
  almost 
  arresting 
  for 
  a 
  time 
  the 
  prog- 
  

   ress 
  of 
  degradation. 
  I 
  imagine 
  that 
  upon 
  close 
  examination 
  the 
  strata 
  

   comprising 
  it 
  would 
  not 
  be 
  found 
  to 
  possess 
  a 
  much 
  greater 
  degree 
  of 
  firm- 
  

   ness 
  than 
  the 
  sandstones 
  of 
  the 
  Mesa 
  Verde 
  group, 
  and 
  they 
  are 
  cer- 
  

   tainly 
  less 
  massive 
  ', 
  but 
  when 
  we 
  consider 
  that 
  the 
  former 
  group 
  rests 
  

   upon 
  a 
  series 
  of 
  moderately 
  compact 
  rocks, 
  while 
  the 
  latter 
  are 
  under- 
  

   laid 
  by 
  1,400 
  feet 
  of 
  exceedingly 
  friable 
  strata, 
  and, 
  further, 
  that 
  these 
  

   firm 
  rocks 
  yield 
  more 
  by 
  undermining 
  and 
  breaking 
  down 
  than 
  by 
  actual 
  

   disintegration, 
  we 
  can 
  understand 
  the 
  reasons^for 
  such 
  successful 
  resist- 
  

   ance. 
  

  

  Over 
  hundreds 
  of 
  square 
  miles 
  these 
  sandstones 
  lie 
  comparatively 
  

   unbroken, 
  while 
  the 
  loose 
  series 
  of 
  shales 
  above 
  have 
  been 
  swept 
  off 
  

   like 
  so 
  much 
  dust 
  from 
  a 
  great 
  floor. 
  This 
  condition 
  of 
  things 
  is 
  espe- 
  

   cially 
  noticeable 
  in 
  the 
  region 
  of 
  the 
  Great 
  Sage 
  Plain 
  between 
  the 
  

   Dolores 
  and 
  the 
  Lower 
  San 
  Juan. 
  It 
  has, 
  where 
  remaining 
  in 
  its 
  undis- 
  

   turbed 
  horizontal 
  position, 
  only 
  been 
  penetrated 
  in 
  the 
  deeper 
  parts 
  of 
  

   the 
  canons 
  of 
  the 
  San 
  Juan 
  and 
  Dolores 
  Rivers. 
  In 
  these 
  caiions 
  the 
  

   Red-Beds 
  are 
  exposed. 
  Along 
  the 
  bases 
  of 
  the 
  La 
  Plata 
  and 
  San 
  Juan 
  

   Mountains 
  it 
  has 
  been 
  turned 
  up 
  against 
  the 
  slopes, 
  and 
  generally 
  where 
  

   outcropping 
  forms 
  a 
  prominent 
  hog-back 
  ridge. 
  

  

  At 
  the 
  exit 
  of 
  the 
  Rio 
  La 
  Plata 
  from 
  the 
  mountains, 
  less 
  than 
  a 
  mile 
  

   above 
  Parrott 
  City, 
  it 
  outcrops 
  in 
  the 
  river 
  banlis, 
  and 
  dips 
  away 
  from 
  

   the 
  mountains 
  at 
  a 
  high 
  angle. 
  Here 
  as 
  elsewhere 
  it 
  contains 
  near 
  the 
  

   top 
  one 
  or 
  more 
  seams 
  of 
  coal. 
  The 
  quality 
  of 
  this 
  coal 
  is 
  always 
  good, 
  

   but 
  is 
  not 
  known 
  in 
  Colorado 
  to 
  reach 
  a 
  thickness 
  above 
  3 
  or 
  4 
  feet. 
  

  

  West 
  of 
  the 
  Rio 
  La 
  Plata 
  the 
  sandstones 
  of 
  this 
  group 
  may 
  be 
  seen 
  

  

  