﻿88 
  REPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  and 
  No. 
  4. 
  The 
  division 
  was 
  made 
  lithologically, 
  and 
  the 
  line 
  perhaps 
  

   should 
  be 
  drawn 
  somewhat 
  lower 
  down, 
  so 
  as 
  to 
  include 
  a 
  portion 
  of 
  No. 
  

   4 
  with 
  the 
  upper 
  division. 
  Professor 
  Meek 
  is 
  inclined 
  to 
  place 
  the 
  line 
  

   separating 
  the 
  Middle 
  Cretaceous 
  from 
  the 
  Upper 
  at 
  the 
  base 
  of 
  No. 
  4. 
  

   He 
  says 
  the 
  fossils 
  never 
  cross 
  the 
  line, 
  and 
  that 
  the 
  division 
  corre- 
  

   sponds 
  more 
  nearly 
  with 
  the 
  European 
  divisions. 
  The 
  Cretaceous 
  

   strata 
  once 
  probably 
  extended 
  over 
  our 
  entire 
  district, 
  and 
  where 
  Iiow 
  

   absent 
  it 
  is 
  due 
  to 
  erosion. 
  

  

  LOWER 
  CRETACEOUS. 
  

  

  Dakota 
  group. 
  — 
  (Formation 
  No. 
  ] 
  .) 
  — 
  Nothing 
  was 
  obtained 
  from 
  the 
  

   Dakota 
  sandstone 
  during 
  the 
  season 
  from 
  which 
  anything 
  new 
  can 
  be 
  

   predicated 
  in 
  regard 
  to 
  the 
  formation. 
  The 
  massive 
  yellow 
  siliceous 
  

   sandstone, 
  in 
  some 
  places 
  quartzitic, 
  at 
  the 
  base 
  of 
  the 
  Cretaceous 
  is 
  so 
  

   well 
  defined 
  lithologically 
  that 
  there 
  has 
  never 
  been 
  any 
  difficulty 
  in 
  

   separating 
  it 
  from 
  the 
  overlying 
  shales. 
  Along 
  the 
  edge 
  of 
  the 
  plains 
  in 
  

   Colorado 
  it 
  is 
  underlaid 
  by 
  greenish 
  shaly 
  beds, 
  sometimes 
  lignitic 
  

   near 
  the 
  top, 
  generally 
  in 
  part 
  or 
  wholly 
  covered, 
  which 
  have 
  always 
  

   been 
  referred 
  to 
  the 
  upper 
  part 
  of 
  the 
  Jurassic. 
  In 
  the 
  West 
  these 
  

   shaly 
  beds 
  still 
  persist, 
  and 
  the 
  massive 
  sandstone, 
  although 
  still 
  recog- 
  

   nizable 
  without 
  difficulty, 
  is 
  much 
  thinner, 
  being 
  only 
  from 
  50 
  to 
  100 
  

   feet, 
  and 
  as 
  we 
  descend 
  in 
  the 
  sections 
  carried 
  below 
  we 
  find 
  other 
  beds 
  

   of 
  siliceous 
  sandstone 
  separated 
  by 
  shaly 
  beds 
  that 
  are 
  arenaceors, 
  

   calcareous, 
  and 
  argillaceous. 
  In 
  these 
  beds, 
  in 
  1874, 
  I 
  found 
  a 
  s-fc,sa- 
  

   fras-leaf, 
  which 
  led 
  me 
  to 
  refer 
  these 
  lower 
  beds 
  to 
  the 
  Lower 
  Cretaceous, 
  

   I 
  drew 
  an 
  arbitrary 
  line 
  separating 
  the 
  Cretaceous 
  and 
  Jurassic. 
  The 
  

   beds 
  below 
  have 
  the 
  same 
  lithological 
  characters 
  to 
  the 
  top 
  of 
  the 
  red 
  

   beds, 
  with 
  this 
  exception, 
  that 
  limestones 
  occur 
  more 
  frequently 
  toward 
  

   the 
  base. 
  In 
  New 
  Mexico 
  and 
  Southwestern 
  Colorado, 
  Dr. 
  Neyberry 
  

   describes 
  two 
  groups, 
  which 
  he 
  refers 
  to 
  the 
  Dakota 
  group 
  or 
  Lower 
  

   division 
  of 
  the 
  Cretaceous. 
  In 
  Mr. 
  Holmes's 
  district 
  these 
  groups 
  are 
  

   distinct, 
  and 
  he 
  proposes 
  to 
  call 
  them 
  Upper 
  and 
  Lower 
  Dakota. 
  In 
  

   Middle 
  Park, 
  in 
  1873, 
  Mr. 
  Marvine 
  found 
  a 
  series 
  of 
  shaly 
  beds 
  with 
  thick 
  

   beds 
  of 
  siliceous 
  sandstone 
  resting 
  on 
  the 
  granite, 
  with 
  the 
  massive 
  

   sandstone 
  of 
  No. 
  1 
  above. 
  These 
  lower 
  beds 
  he 
  referred 
  to 
  the 
  same 
  

   formation.* 
  In 
  the 
  Black 
  Hills 
  the 
  Dakota 
  group 
  is 
  represented 
  by 
  a 
  

   series 
  of 
  alternating 
  sandstones 
  and 
  clays.t 
  

  

  In 
  Arizona, 
  G. 
  K. 
  Gilbert 
  found 
  Jurassic 
  and 
  Cretaceous 
  fossils 
  asso- 
  

   ciated 
  in 
  beds, 
  resembling 
  those 
  usually 
  referred 
  to 
  the 
  Jurassic. 
  I 
  am 
  

   of 
  the 
  opinion 
  that 
  we 
  cannot 
  draw 
  any 
  line 
  between 
  the 
  two 
  forma- 
  

   tions, 
  paleontologically 
  nor 
  lithologically, 
  but 
  for 
  convenience 
  in 
  descrip- 
  

   tion 
  it 
  is 
  best 
  to 
  draw 
  an 
  arbitrary 
  line, 
  which 
  may 
  be 
  changed 
  as 
  we 
  

   obtain 
  more 
  facts 
  in 
  relation 
  to 
  the 
  formation. 
  These 
  beds 
  and 
  those 
  

   just 
  beneath, 
  that 
  I 
  have 
  referred 
  to 
  the 
  Jura, 
  are 
  those 
  that 
  have 
  been 
  

   called 
  the 
  variegated 
  marls 
  in 
  Arizona 
  and 
  New 
  Mexico. 
  The 
  upper 
  

   massive 
  sandstone 
  of 
  the 
  Dakota 
  group 
  forms 
  the 
  surface 
  generally, 
  with 
  

   the 
  lower 
  shaly 
  beds 
  outcropping 
  in 
  the 
  canons. 
  

  

  On 
  the 
  south 
  side 
  of 
  the 
  Gunnison, 
  above 
  the 
  Grand 
  Canon, 
  there 
  is 
  

   a 
  narrow 
  outcrop 
  of 
  No. 
  1 
  between 
  the 
  breccia 
  and 
  the 
  granite. 
  A 
  few 
  

   miles 
  south 
  of 
  the 
  Gunnison 
  it 
  has 
  disappeared. 
  

  

  At 
  the 
  head 
  of 
  the 
  Uncompahgre 
  Kiver 
  and 
  on 
  the 
  Dallas 
  Foik, 
  No. 
  

   1 
  appears, 
  and 
  is 
  faulted, 
  the 
  latter 
  stream 
  flowing 
  on 
  the 
  line 
  of 
  the 
  

  

  •Report 
  United 
  States 
  Geological 
  Survey 
  1873, 
  pp. 
  155, 
  156. 
  

  

  t 
  Geological 
  Report 
  Exploration 
  of 
  Yellowstone 
  and 
  Missouri 
  Rivers, 
  pp. 
  15, 
  42, 
  43. 
  

  

  