﻿HOLMES.] 
  - 
  MIDDLE 
  CRETACEOUS 
  FORMATIONS. 
  253 
  

  

  bearing 
  rocks, 
  and 
  above 
  these 
  two 
  groups 
  of 
  sandstone, 
  the 
  Upper 
  Es- 
  

   carpment 
  and 
  the 
  Pinon 
  Mesa 
  Groups 
  (6 
  and 
  1), 
  which 
  are 
  somewhat 
  

   alike; 
  also, 
  the 
  fossil-bearing 
  limestone,' 
  which 
  occurs 
  near 
  the 
  base 
  of 
  

   group 
  5, 
  is 
  apparently 
  repeated 
  in 
  a 
  bed 
  of 
  rusty 
  limestone 
  (9) 
  that 
  

   occurs 
  beneath 
  the 
  Lower 
  Escarpment 
  and 
  in 
  the 
  upper 
  part 
  of 
  the 
  

   Middle 
  Cretaceous 
  shales. 
  The 
  displacement 
  or 
  throw 
  indicated 
  by 
  

   these 
  facts 
  would 
  be 
  about 
  1,500 
  feet, 
  and 
  if 
  proven 
  to 
  exist 
  would 
  

   change 
  my 
  section 
  so 
  as 
  to 
  place 
  group 
  1 
  immediately 
  upon 
  group 
  7, 
  

   and 
  the 
  1,500 
  feet 
  between 
  would 
  drop 
  out 
  of 
  the 
  section. 
  But 
  the 
  

   evidences 
  against 
  the 
  existence 
  of 
  such 
  a 
  displacement 
  are 
  very 
  strong, 
  

   if 
  not 
  conclusive. 
  The 
  Coal 
  Group 
  of 
  the 
  Hogback 
  (group 
  7) 
  is 
  totally 
  

   unlike 
  the 
  Upper 
  Coal 
  Group 
  (3). 
  In 
  group 
  7 
  the 
  entire 
  thickness 
  is 
  only 
  

   800 
  feet, 
  and 
  the 
  strata 
  are 
  chiefly 
  sandstones 
  and 
  shales, 
  which, 
  toward 
  

   the 
  top, 
  have 
  a 
  number 
  of 
  seams 
  of 
  coal 
  ; 
  farther 
  west 
  and 
  northj 
  in 
  the 
  

   Mesa 
  Verde, 
  the 
  sandstones 
  predominate. 
  In 
  group 
  3 
  the 
  coal 
  occurs 
  

   iu 
  a 
  heavy 
  seam 
  at 
  the 
  very 
  base, 
  the 
  mass 
  of 
  the 
  strata 
  being 
  yellow 
  

   sandstones, 
  which 
  bear 
  no 
  coal 
  toward 
  the 
  top, 
  while 
  group 
  2, 
  the 
  bad- 
  

   land 
  marls, 
  has 
  no 
  place 
  or 
  corresponding 
  group 
  in 
  the 
  section 
  of 
  the 
  

   Hogback. 
  These 
  differences 
  are 
  constant 
  throughout 
  the 
  area 
  exam- 
  

   ined 
  by 
  me. 
  The 
  section 
  on 
  the 
  La 
  Plata 
  has 
  the 
  same 
  succession 
  of 
  

   groups 
  ,as 
  this 
  on 
  the 
  San 
  Juan. 
  Dr. 
  Endlich 
  has 
  the 
  same 
  near 
  the 
  

   Eio 
  Florida, 
  and 
  Messrs. 
  Dwire 
  and 
  Hendrickson 
  observed 
  the 
  same 
  suc- 
  

   cession 
  of 
  strata, 
  the 
  same 
  arrangement 
  of 
  the 
  «oal 
  groups 
  and 
  corre- 
  

   sponding 
  thicknesses 
  of 
  beds 
  on 
  the 
  Animas. 
  In 
  all 
  of 
  these 
  cases 
  the 
  

   exposures 
  are 
  so 
  complete 
  that 
  a 
  fault 
  could 
  hardly 
  exist 
  without 
  being 
  

   detected. 
  Dr. 
  Newberry, 
  who 
  passed 
  up 
  the 
  San 
  Juan 
  in 
  1859, 
  states 
  

   that 
  a 
  fault 
  or 
  rupture 
  occurs 
  in 
  the 
  region 
  of 
  the 
  Great 
  Hogback, 
  but 
  

   he 
  seems 
  to 
  have 
  observed 
  no 
  evidence 
  of 
  it 
  except 
  the 
  apparent 
  dupli- 
  

   cation 
  of 
  strata. 
  

  

  In 
  Plate 
  XXXIX 
  I 
  present 
  a 
  sketch 
  of 
  an 
  interesting 
  system 
  of 
  ter- 
  

   races 
  that 
  occurs 
  on 
  the 
  south 
  side 
  of 
  the 
  river. 
  They 
  cover 
  a 
  large 
  

   area 
  about 
  the 
  Great 
  Hogback, 
  and 
  seem 
  to 
  have 
  uniform 
  levels 
  both 
  

   east 
  and 
  west 
  of 
  it. 
  Portions 
  of 
  the 
  Hogback 
  have 
  been 
  planed 
  down 
  

   to 
  the 
  level 
  of 
  the 
  upper 
  terrace, 
  more 
  limited 
  portions 
  to 
  the 
  level 
  of 
  

   the 
  second, 
  a 
  few 
  buttes 
  of 
  outcropping 
  strata 
  protruding 
  above, 
  and 
  

   a 
  very 
  narrow 
  belt 
  to 
  the 
  lower 
  level, 
  while 
  the 
  river 
  has 
  cut 
  a 
  passage 
  

   barely 
  wide 
  enough 
  for 
  its 
  own 
  accommodation. 
  

  

  MESA 
  VERDE. 
  

  

  As 
  already 
  mentioned 
  in 
  the 
  preceding 
  pages, 
  the 
  San 
  Juan 
  fold 
  

   begins 
  along 
  the 
  south 
  base 
  of 
  the 
  La 
  Plata 
  Mountains 
  and 
  extends 
  in 
  

   a 
  southwest 
  direction 
  to 
  the 
  San 
  Juan 
  River, 
  which 
  it 
  crosses 
  at 
  the 
  

   Great 
  Hogback. 
  East 
  of 
  the 
  fold 
  the 
  Eocene 
  (!) 
  formations 
  occupy 
  

   the 
  surface 
  of 
  the 
  country 
  ; 
  west 
  of 
  it 
  we 
  have 
  nothing 
  but 
  Cretaceous 
  

   rocks. 
  The 
  heavy 
  sandstones 
  of 
  the 
  Mesa 
  Verde 
  group 
  rise 
  to 
  the 
  sur- 
  

   face 
  along 
  the 
  axis 
  of 
  the 
  fold 
  and 
  in 
  a 
  comparatively 
  gentle 
  slope 
  

   reach 
  a 
  level 
  more 
  than 
  1,000 
  feet 
  above 
  that 
  occupied 
  by 
  the 
  same 
  

   beds 
  east 
  of 
  the 
  fold; 
  afterward 
  they 
  flatten 
  out 
  and 
  form 
  the 
  Mesa 
  

   Verde 
  (see 
  bird's-eye 
  view, 
  Plate 
  XXXVI). 
  This 
  table-land 
  is 
  one 
  of 
  the 
  

   grand 
  features 
  of 
  this 
  part 
  of 
  the 
  great 
  Colorado 
  Plateau, 
  which, 
  al- 
  

   though 
  rising 
  so 
  gradually 
  on 
  the 
  east, 
  presents 
  a 
  magnificent 
  series 
  of 
  

   cliffs 
  on 
  the 
  north, 
  south, 
  and 
  west. 
  Over 
  the 
  greater 
  part 
  of 
  the 
  area, 
  

   which 
  comprises 
  some 
  90 
  square 
  miles, 
  the 
  general 
  level 
  is 
  well 
  sustained- 
  

   by 
  the 
  massive 
  layer 
  of 
  sandstone 
  of 
  the 
  Upper 
  Escarpment, 
  not 
  as 
  an 
  

   unbroken 
  mass 
  of 
  block 
  of 
  strata 
  of 
  course, 
  for 
  the 
  erosive 
  forces 
  have 
  iu- 
  

  

  