﻿258 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  to 
  the 
  height 
  of 
  20 
  or 
  30 
  feet. 
  The 
  only 
  considerable 
  bluff 
  occurs 
  some 
  

   20 
  miles 
  below 
  the 
  Hogback, 
  and 
  consists 
  of 
  the 
  firm 
  shales 
  and 
  impure 
  

   siliceous 
  limestones 
  which 
  contain 
  such 
  quantities 
  of 
  fossils 
  — 
  including 
  

   Baculites^ 
  BcapliUes^ 
  Ostrea, 
  &c. 
  A 
  short 
  distance 
  below 
  this 
  the 
  sand- 
  

   stones 
  of 
  the 
  Dakota 
  group 
  rise 
  to 
  the 
  surface. 
  The 
  section 
  of 
  the 
  

   Middle 
  Cretaceous 
  strata, 
  as 
  exposed 
  on 
  the 
  San 
  Juan, 
  will 
  be 
  about 
  as 
  

   follows 
  : 
  

  

  Beginning 
  at 
  the 
  base 
  of 
  the 
  Hogback, 
  we 
  have 
  — 
  

   200 
  feet 
  of 
  sandy 
  shales, 
  gray 
  and 
  yellowish. 
  

   10 
  feet 
  of 
  ferruginous, 
  shaly 
  limestone, 
  containing 
  bed 
  of 
  Inocera- 
  

   mus. 
  

   700 
  feet 
  of 
  shales, 
  sandy, 
  argillaceous, 
  and 
  calcareous. 
  

   12 
  feet 
  of 
  siliceous 
  limestone, 
  containing 
  many 
  well-preserved 
  

   specimens 
  of 
  Sca])Mtes 
  Warrenii, 
  Inoceranius 
  Barabini, 
  and 
  

   Baculites 
  ovatvs. 
  

   400 
  feet 
  of 
  shales 
  bearing 
  heavy 
  deposits 
  of 
  Ostrea 
  and 
  Orypliea. 
  

   Near 
  the 
  base 
  a 
  considerable 
  seam 
  of 
  coal 
  occurs. 
  This 
  group 
  

   of 
  shales 
  rests 
  upon 
  the 
  Dakota 
  sandstones. 
  

  

  The 
  bed 
  of 
  siliceous 
  limestones 
  correspond 
  to 
  a 
  group 
  of 
  fossiliferous 
  

   limestones 
  that 
  occurs 
  everywhere 
  along 
  the 
  eastern 
  base 
  of 
  the 
  mount- 
  

   ains, 
  and 
  which 
  is 
  usually 
  considered 
  a 
  part 
  of 
  No. 
  2 
  Cretaceous. 
  In 
  

   this 
  valley 
  it 
  is 
  the 
  only 
  stratum 
  belonging 
  to 
  the 
  Middle 
  Cretaceous 
  

   which 
  has 
  sufficient 
  firmness 
  to 
  produce 
  a 
  line 
  of 
  well-marked 
  bluffs. 
  

  

  Near 
  the 
  river 
  these 
  bluffs 
  rise 
  to 
  the 
  height 
  of 
  30 
  or 
  40 
  feet 
  ; 
  on 
  the 
  

   south 
  side 
  they 
  form 
  the 
  east 
  banks 
  of 
  Eed 
  Creek, 
  which 
  are 
  in 
  i)laces 
  

   nearly 
  200 
  feet 
  in 
  height. 
  North 
  from 
  the 
  river 
  they 
  may 
  be 
  traced 
  to 
  

   the 
  Mancos 
  River 
  and 
  beyond, 
  around 
  the 
  west 
  base 
  of 
  the 
  Late 
  Mount- 
  

   ains. 
  The 
  section 
  of 
  Middle 
  Cretaceous 
  rocks 
  en 
  the 
  Mancos 
  does 
  not 
  

   differ 
  greatly 
  from 
  that 
  of 
  the 
  San 
  Juan. 
  

  

  North 
  of 
  the 
  Mancos 
  the 
  shales 
  do 
  not 
  reach 
  west 
  beyond 
  the 
  San 
  

   Juan, 
  but 
  in 
  a 
  number 
  of 
  places 
  cap 
  the 
  bluffs 
  on 
  the 
  east 
  side. 
  They 
  

   surround 
  to 
  a 
  great 
  extent 
  the 
  trachytic 
  masses 
  of 
  the 
  Late 
  Mountains, 
  

   and 
  occur 
  on 
  the 
  higher 
  parts 
  of 
  the 
  table-land 
  that 
  lies 
  between 
  the 
  

   lower 
  McBlmo 
  and 
  the 
  San 
  Juan. 
  In 
  many 
  places 
  they 
  appear 
  to 
  be 
  

   tipped 
  up 
  against 
  the 
  bases 
  of 
  the 
  Late 
  Mountains, 
  and 
  large 
  fragments 
  

   of 
  shales 
  are 
  carried 
  high 
  up 
  on 
  the 
  trachytic 
  summits. 
  The 
  low 
  puerta 
  

   between 
  the 
  Late 
  Mountains 
  and 
  the 
  Mesa 
  Verde 
  is 
  occupied 
  entirely 
  

   by 
  the 
  shales, 
  and 
  the 
  ancient 
  village 
  which 
  lies 
  at 
  the 
  highest 
  part 
  of 
  

   the 
  puerta 
  and 
  on 
  the 
  divide 
  between 
  the 
  Mancos 
  and 
  McElmo 
  has 
  been 
  

   constructed 
  chiefly 
  of 
  the 
  fossil-bearing 
  siliceous 
  limestone 
  mentioned 
  in 
  

   the 
  last 
  section. 
  In 
  Figure 
  1, 
  Plate 
  XL, 
  is 
  given 
  a 
  profile 
  of 
  the 
  west- 
  

   ern 
  face 
  of 
  the 
  mesa, 
  the 
  Late 
  Mountains, 
  and 
  the 
  puerta 
  between. 
  

  

  Along 
  the 
  northwest 
  face 
  of 
  the 
  Mesa 
  Verde 
  the 
  shales 
  occupy 
  a 
  belt 
  

   from 
  four 
  to 
  six 
  miles 
  in 
  width. 
  The 
  greater 
  part 
  of 
  the 
  series 
  outcrops 
  

   along 
  the 
  steep 
  slope 
  of 
  the 
  mesa. 
  Between 
  the 
  headwaters 
  of 
  the 
  

   McElmo 
  and 
  the 
  Mancos, 
  extending 
  northward 
  from 
  the 
  mesa 
  prom- 
  

   ontories, 
  are 
  a 
  great 
  number 
  of 
  rounded 
  buttes 
  composed 
  of 
  dark 
  shales. 
  

   About 
  the 
  bases 
  of 
  these 
  buttes 
  great 
  quantities 
  of 
  Grypheas 
  and 
  Oysters 
  

   may 
  be 
  seen. 
  They 
  are 
  weathered 
  out 
  and 
  lie 
  about 
  in 
  heaps. 
  

  

  As 
  has 
  already 
  been 
  stated 
  in 
  the 
  preceding 
  pages, 
  the 
  long, 
  narrow 
  

   puerta 
  or 
  pass 
  which 
  separates 
  the 
  La 
  Plata 
  Mountains 
  from 
  the 
  Mesa 
  

   Verde, 
  and 
  connects 
  the 
  valleys 
  of 
  the 
  Mancos 
  and 
  La 
  Plata 
  Elvers, 
  is 
  

   eroded 
  from 
  the 
  Cretaceous 
  shales. 
  The 
  La 
  Plata 
  gold 
  bar 
  has 
  been 
  de- 
  

   posited 
  on 
  the 
  upturned 
  edges 
  of 
  the 
  shales 
  and 
  the 
  fossil- 
  bearing 
  lime- 
  

   stone 
  passes 
  beneath 
  Parrott 
  City. 
  Between 
  the 
  town 
  and 
  the 
  La 
  Plata 
  

   Eiver 
  a 
  low 
  ridge, 
  composed 
  of 
  this 
  limestone, 
  appears 
  above 
  the 
  bar 
  

  

  