﻿PEALE.] 
  

  

  MESOZOIC 
  FOEMATIONS 
  LOWER 
  CRETACEOUS. 
  89 
  

  

  fault. 
  Between 
  this 
  creek 
  and 
  the 
  San 
  Juan 
  Mountains 
  the 
  Dakota 
  

   group 
  rises 
  until 
  it 
  reaches 
  the 
  summit 
  of 
  the 
  foot-hills, 
  appearing 
  from 
  

   beneath 
  the 
  shales. 
  On 
  the 
  Uncompahgre 
  Plateau 
  the 
  Dakota 
  group, 
  

   dipping 
  gently 
  to 
  the 
  eastward, 
  is 
  the 
  surface 
  formation 
  until 
  we 
  ap- 
  

   proach 
  Bscalante 
  Greek. 
  Between 
  the 
  latter 
  and 
  Koubideau's 
  Creek, 
  

   there 
  are 
  some 
  isolated 
  patches 
  of 
  Eo. 
  1. 
  Along 
  the 
  western 
  side 
  of 
  

   the 
  Gunnison, 
  also, 
  we 
  find 
  the 
  Dakota 
  group. 
  The 
  floor 
  of 
  the 
  San 
  

   Miguel 
  plateau 
  is 
  made 
  of 
  the 
  Dakota 
  group, 
  and 
  in 
  the 
  deeper 
  canons 
  

   cut 
  in 
  it, 
  a 
  narrow 
  band 
  of 
  Jura 
  shows. 
  The 
  consideration 
  of 
  the 
  Da- 
  

   kota 
  group 
  west 
  of 
  the 
  San 
  Miguel 
  will 
  have 
  to 
  be 
  reserved. 
  Going 
  

   north 
  on 
  the 
  San 
  Miguel 
  plateau, 
  we 
  find 
  the 
  massive 
  sandstones 
  of 
  the 
  

   Dakota 
  group 
  broken 
  and 
  forming 
  the 
  tops 
  of 
  mesas 
  between 
  the 
  streams 
  

   rising 
  in 
  the 
  Uncompahgre 
  Plateau 
  and 
  flowing 
  into 
  the 
  San 
  Miguel 
  and 
  

   Dolores 
  Eivers. 
  Still 
  farther 
  north 
  the 
  No. 
  1 
  disappears 
  altogether, 
  

   until 
  we 
  approach 
  Grand 
  River, 
  near 
  the 
  mouth 
  of 
  the 
  Dolores. 
  In 
  the 
  

   Uncompahgre 
  Plateau, 
  as 
  I 
  have 
  already 
  noted, 
  the 
  No. 
  1 
  dips 
  toward 
  

   the 
  Uncompahgre. 
  This 
  plateau 
  is 
  separated 
  from 
  the 
  San 
  Miguel 
  by 
  

   a 
  monoclinal 
  fold, 
  which 
  at 
  first 
  is 
  complete 
  as 
  far 
  as 
  the 
  Dakota 
  group 
  

   is 
  concerned. 
  In 
  the 
  San 
  Miguel 
  Plateau 
  the 
  beds 
  are 
  nearly 
  horizontal. 
  

   There 
  is 
  a 
  slight 
  anticlinal 
  swell 
  between 
  the 
  San 
  Miguel 
  River 
  and 
  the 
  

   monoclinal 
  fold. 
  As 
  we 
  follow 
  the 
  latter 
  north, 
  we 
  find 
  the 
  fold 
  more 
  

   abrupt, 
  and 
  the 
  upper 
  beds 
  eroded 
  away, 
  and 
  still 
  farther 
  along, 
  as 
  has 
  

   been 
  described 
  in 
  previous 
  portions 
  of 
  the 
  report, 
  we 
  have 
  a 
  fault. 
  

  

  ^n 
  the 
  region 
  of 
  the 
  Sierra 
  la 
  Sal, 
  No. 
  1 
  is 
  present, 
  on 
  the 
  west 
  side, 
  

   dipt 
  ig 
  away 
  from 
  the 
  mountains 
  at 
  a 
  steep 
  angle. 
  The 
  reference 
  of 
  

   the 
  sandstones 
  and 
  shales 
  just 
  described 
  to 
  the 
  Dakota 
  group 
  rests 
  

   mainly 
  on 
  lithological 
  and 
  stratigraphical 
  evidence. 
  In 
  Eastern 
  Colo- 
  

   rado, 
  Dr. 
  Hayden 
  has 
  considered 
  them 
  identical 
  with 
  the 
  Dakota 
  group 
  

   in 
  Kansas 
  and 
  Nebraska. 
  In 
  both 
  localities 
  they 
  are 
  underlaid 
  by 
  the 
  

   same 
  character 
  of 
  beds, 
  and 
  above 
  are 
  well-marked 
  Cretaceous 
  fossils, 
  and 
  

   there 
  is 
  a 
  general 
  resemblance 
  lithologically 
  . 
  The 
  list 
  of 
  fossils 
  obtained 
  

   from 
  the 
  beds 
  in 
  Colorado 
  is 
  meager 
  as 
  yet. 
  It 
  is 
  as 
  follows 
  : 
  

  

  Proteoides 
  like 
  P. 
  acuta, 
  Heer, 
  edge 
  of 
  plains 
  on 
  South 
  Platte 
  River. 
  

  

  Sassafras 
  like 
  S. 
  mirabile 
  on 
  Gunnison 
  River. 
  

  

  Salix 
  f 
  in 
  the 
  Elk 
  Mountains. 
  

  

  Fragments 
  of 
  dicotyledonous 
  leaves, 
  on 
  the 
  Gunnison 
  and 
  in 
  the 
  

   Elk 
  Mountains. 
  

  

  Scapliites 
  f 
  on 
  Gunnison 
  River. 
  

  

  Lingula 
  ? 
  near 
  Colorado 
  Springs. 
  

  

  In 
  the 
  Report 
  for 
  1874 
  I 
  pointed 
  out 
  the 
  resemblance 
  of 
  my 
  sections 
  to 
  

   those 
  of 
  Dr. 
  Newberry. 
  In 
  Northeast 
  New 
  Mexico 
  and 
  Southeast 
  Utah 
  

   Dr. 
  Newberry 
  recognizes 
  the 
  Dakota 
  group, 
  and 
  the 
  beds 
  are 
  the 
  same 
  

   that 
  I 
  have 
  so 
  referred 
  and 
  traced 
  from 
  Eastern 
  Colorado 
  to 
  Western 
  

   Colorado 
  and 
  Southeastern 
  Utah, 
  joining 
  the 
  region 
  investigated 
  by 
  Dr. 
  

   Newberry. 
  Additional 
  facts 
  in 
  regard 
  to 
  the 
  Dakota 
  group 
  in 
  that 
  

   region 
  will 
  be 
  presented 
  by 
  Mr. 
  Holmes 
  in 
  his 
  report. 
  Powell, 
  in 
  speak- 
  

   ing 
  of 
  what 
  he 
  calls 
  the 
  Plateau 
  Province, 
  says 
  :* 
  

  

  Planes 
  of 
  demarkation 
  in 
  the 
  Cretaceous 
  group 
  are 
  not 
  easily 
  drawn 
  The 
  relation 
  of 
  these 
  

   groups 
  to 
  those 
  established 
  by 
  Professors 
  Meek 
  and 
  Hayden 
  on 
  the 
  Upper 
  Missouri 
  is 
  not 
  

   ■well 
  determined. 
  I 
  have 
  carefully 
  tried 
  to 
  use 
  their 
  system, 
  and 
  have 
  failed. 
  

  

  The 
  Henry's 
  Fork 
  group, 
  which 
  Powell 
  places 
  at 
  the 
  base 
  of 
  the 
  Cre- 
  

   taceous, 
  is 
  evidently, 
  in 
  part 
  at 
  least, 
  the 
  Dakota 
  group 
  of 
  Meek 
  and 
  

   Hayden. 
  In 
  the 
  reportt 
  he 
  gives 
  the 
  south 
  side 
  of 
  Henry's 
  Fork, 
  

  

  * 
  Report 
  on 
  the 
  Geology 
  of 
  the 
  Eastern 
  Portion 
  of 
  the 
  Uinta 
  Mountains, 
  &c., 
  p. 
  67. 
  

   t 
  Ibid., 
  pp. 
  50,51. 
  

  

  