﻿HOLMES] 
  CRETACEOUS 
  AND 
  TEETIARY 
  FORMATIONS. 
  251 
  

  

  tion. 
  The 
  dip 
  at 
  the 
  base 
  of 
  the 
  Pictured 
  Cliff 
  is 
  not 
  above 
  2° 
  ; 
  midway 
  

   betweeu 
  this 
  and 
  the 
  Great 
  Hogback 
  the 
  beds 
  fall 
  to 
  the 
  horizontal 
  and 
  

   remain 
  nearly 
  so 
  until 
  turned 
  abruptly 
  up 
  against 
  the 
  sandstones 
  of 
  the 
  

   hogback. 
  The 
  upper 
  part 
  of 
  group 
  5 
  is 
  composed 
  of 
  clays, 
  argillaceous 
  

   shale 
  and 
  sands, 
  greenish 
  toward 
  the 
  base. 
  In 
  the 
  lower 
  part 
  there 
  are 
  

   thin 
  layers 
  of 
  sandstone, 
  and 
  near 
  the 
  base 
  a 
  stratum 
  of 
  rusty 
  lime- 
  

   stone, 
  in 
  which 
  I 
  obtained 
  specimens 
  of 
  Inoceramus, 
  Lucina, 
  BacuUtes^ 
  

   and 
  Anisomyon. 
  The 
  detailed 
  section 
  of 
  the 
  strata 
  exposed 
  on 
  the 
  San 
  

   Juan 
  down 
  to 
  the 
  Great 
  Hogback 
  is 
  as 
  follows 
  : 
  

  

  Pifion 
  Mesa 
  sandstones, 
  groui? 
  1 
  1,200 
  feet. 
  

  

  Chiefly 
  coarse, 
  yellowish 
  sandstones, 
  alternating 
  with 
  

   thin 
  beds 
  of 
  variagated 
  marls. 
  

  

  Bad 
  Land 
  formation, 
  group 
  2 
  = 
  ,.... 
  600 
  feet. 
  

  

  Variegated 
  marls 
  containing, 
  toward 
  the 
  base, 
  layers 
  

   of 
  yellowish 
  sandstone. 
  

  

  Upper 
  Coal 
  series, 
  group 
  3 
  700 
  feet. 
  

  

  Soft, 
  yellow 
  sandstones, 
  interbedded 
  with 
  sands, 
  

   clays, 
  and 
  shales; 
  one 
  seam 
  of 
  lignite 
  near 
  base, 
  26 
  feet 
  

   exposed. 
  

  

  Pictured 
  Cliffs, 
  group 
  4 
  140 
  feet. 
  

  

  Forty 
  feet 
  of 
  white 
  sandstone; 
  60 
  to 
  80 
  feet 
  yellowish- 
  

   gray 
  sandstone. 
  Beneath 
  these 
  30 
  to 
  40 
  feet 
  of 
  brown- 
  

   ish 
  laminated 
  sandstones. 
  Fossil 
  horizon 
  No. 
  1, 
  on 
  

   upper 
  surface 
  of 
  the 
  white 
  sandstone. 
  Fossil 
  horizon 
  

   No. 
  2, 
  in 
  the 
  brownish 
  laminated 
  sandstones. 
  

  

  Sands, 
  clays, 
  and 
  shales, 
  group 
  5 
  600 
  to 
  900 
  feet. 
  

  

  Sands, 
  clays, 
  and 
  shales 
  grayish 
  in 
  color 
  and 
  having 
  

   near 
  the 
  base 
  a 
  bed 
  of 
  brown 
  limestone. 
  This 
  is 
  fossil 
  

   horizon 
  No. 
  3. 
  

  

  THE 
  GREAT 
  HOGBACK. 
  

  

  The 
  Great 
  Hogback 
  is 
  composed 
  of 
  the 
  Mesa 
  Verde 
  Group 
  (groups 
  6, 
  

   7, 
  and 
  8 
  of 
  the 
  general 
  section.) 
  It 
  crosses 
  the 
  river 
  at 
  right 
  angles, 
  hav- 
  

   ing 
  a 
  trend 
  nearly 
  north 
  and 
  south. 
  North 
  of 
  the 
  river 
  it 
  rises 
  abruptly 
  

   to 
  the 
  height 
  of 
  500 
  feet, 
  and 
  extends 
  in 
  an 
  unbroken 
  line 
  northward 
  

   until 
  it 
  joins 
  the 
  Mesa 
  Verde. 
  (See 
  Fig. 
  1, 
  Plate 
  XXXIX.) 
  South 
  of 
  the 
  

   river 
  it 
  has 
  been 
  planed 
  down 
  by 
  the 
  water, 
  nothing 
  appearing 
  above 
  

   the 
  terrace-levels 
  for 
  a 
  mile 
  or 
  more 
  but 
  isolated 
  remnants. 
  Farther 
  

   south 
  it 
  rises 
  in 
  a 
  line 
  of 
  grand 
  ridges 
  which 
  can 
  be 
  traced 
  for 
  many 
  

   miles 
  across 
  the 
  plain 
  country. 
  These 
  ridges 
  are 
  visible 
  from 
  the 
  La 
  

   Plata, 
  the 
  Late, 
  and 
  Carriso 
  ikountains. 
  On 
  the 
  north 
  side 
  the 
  ridge 
  

   is 
  really 
  double, 
  the 
  main 
  eastern 
  crest 
  being 
  formed 
  from 
  the 
  sandstones 
  

   of 
  the 
  Upper 
  Escarpment 
  Group, 
  and 
  the 
  western 
  and 
  subordinate 
  ridge 
  

   of 
  the 
  sandstones 
  of 
  the 
  Lower 
  Escarpment 
  Group. 
  Between 
  these 
  two 
  

   ridges 
  is 
  a 
  sag 
  eroded 
  from 
  the 
  yielding 
  strata 
  of 
  the 
  Middle 
  Coal 
  Group. 
  

   The 
  dip 
  at 
  the 
  river 
  is 
  40°. 
  As 
  we 
  go 
  north 
  the 
  dip 
  rapidly 
  decreases, 
  

   and 
  as 
  a 
  consequence 
  the 
  two 
  ridges 
  become 
  considerably 
  separated. 
  

   The 
  slopes 
  become 
  gentle 
  on 
  the 
  east, 
  and 
  break 
  off 
  abruptly 
  on 
  the 
  west. 
  

   The 
  depression 
  between 
  becomes 
  a 
  shallow 
  valley, 
  and 
  the 
  drainage 
  from 
  

   it 
  passes 
  out 
  through 
  breaks 
  in 
  the 
  western 
  ridge. 
  The 
  dip 
  finally 
  falls 
  

   off' 
  to 
  50 
  and 
  less 
  and 
  the 
  various 
  members 
  of 
  the 
  Hogback 
  may 
  be 
  seen 
  

   connecting 
  on 
  with 
  the 
  corresponding 
  members 
  of 
  the 
  Mesa 
  Verde. 
  The 
  

   main 
  eastern 
  ridge 
  becomes 
  the 
  Upper 
  Escarpment, 
  the 
  western 
  the 
  

  

  