﻿HOLMES.] 
  GENERAL 
  SECTION. 
  243 
  

  

  and 
  numbers 
  and 
  names 
  corresponding 
  to 
  these 
  will 
  be 
  used 
  on 
  all 
  tbe 
  de- 
  

   tailed 
  sections. 
  

  

  The 
  group 
  numbered 
  10 
  in 
  the 
  section 
  is 
  the 
  typical 
  Dakota 
  Sandstones 
  

   of 
  Dr. 
  Hayden. 
  

  

  Groups 
  10 
  and 
  11 
  together, 
  probably 
  constitute 
  the 
  complete 
  Dakota 
  

   Group 
  ; 
  i. 
  e., 
  the 
  Lower 
  Cretaceous 
  of 
  Dr. 
  ISTewberry, 
  and 
  the 
  Henry's 
  

   Fork 
  Group 
  of 
  Major 
  Powell. 
  

  

  Group 
  9 
  is 
  the 
  Cretaceous 
  shales 
  (Cretaceous 
  Nos. 
  2, 
  3, 
  and 
  a 
  part 
  of 
  

   4 
  of 
  Hayden,) 
  the 
  Middle 
  Cretaceous 
  of 
  Newberry, 
  and 
  the 
  Sulphur 
  

   Creek 
  of 
  Powell. 
  

  

  Groups 
  8, 
  7, 
  6, 
  5, 
  and 
  4 
  Cretaceous 
  ISTos. 
  4 
  and 
  5 
  of 
  Hayden, 
  the 
  

   Upper 
  Cretaceous 
  of 
  Newberry, 
  and 
  the 
  Salt 
  Wells 
  of 
  Powell. 
  

  

  Group 
  3 
  is 
  probably 
  the 
  Lignitic 
  coal 
  group 
  of 
  the 
  eastern 
  slope, 
  the 
  

   Laramie 
  Group 
  of 
  King 
  and 
  of 
  Hayden, 
  and 
  the 
  Point 
  of 
  Rocks 
  of 
  

   Powell. 
  

  

  Groups 
  1 
  and 
  2 
  probably 
  correspond 
  to 
  the 
  Wahsatch 
  Group 
  of 
  Hay- 
  

   den 
  and 
  White, 
  and 
  the 
  Vermillion 
  Creek 
  Group 
  of 
  King. 
  

  

  Groups 
  12, 
  13, 
  14, 
  and 
  15 
  are 
  a 
  series 
  of 
  rocks 
  called 
  by 
  some 
  Jurassic, 
  

   by 
  others 
  Triassic, 
  and 
  by 
  still 
  others 
  Jura-Trias. 
  

  

  The 
  Lower 
  Cretaceous 
  sandstones 
  are 
  the 
  most 
  easily 
  recognized 
  and 
  

   by 
  far 
  the 
  most 
  uniform 
  and 
  persistent 
  of 
  the 
  whole 
  section. 
  There 
  is, 
  

   however, 
  considerable 
  difficulty 
  in 
  defining 
  their 
  vertical 
  extent, 
  result- 
  

   ing 
  from 
  the 
  scarcity 
  of 
  fossil 
  remains. 
  The 
  division 
  between 
  these 
  

   sandstones 
  and 
  the 
  shales 
  above 
  is 
  never 
  obscure. 
  In 
  many 
  localities 
  

   which 
  I 
  have 
  examined 
  the 
  line 
  is 
  well 
  marked 
  both 
  by 
  fossils 
  and 
  

   strata 
  ; 
  but 
  it 
  is 
  very 
  difQcult 
  to 
  decide 
  what 
  portion 
  of 
  the 
  strata 
  be- 
  

   neath 
  to 
  include 
  in 
  the 
  group. 
  Ordinarily 
  there 
  are 
  about 
  250 
  feet 
  of 
  

   sandstones 
  and 
  conglomerates 
  about 
  which 
  there 
  can 
  be 
  no 
  dispute 
  

   (these 
  are 
  group 
  10 
  of 
  the 
  section), 
  but 
  beneath 
  these 
  is 
  a 
  series 
  of 
  varie- 
  

   gated 
  marls 
  and 
  sandstones, 
  which 
  have 
  frequently 
  been 
  placed 
  in 
  the 
  

   Jurassic 
  (the 
  upper 
  part 
  of 
  group 
  11). 
  In 
  Eastern 
  Colorado 
  this 
  series 
  is 
  

   so 
  distinct 
  from 
  the 
  more 
  massive 
  beds 
  of 
  the 
  Dakota 
  group 
  that 
  I 
  have 
  

   always 
  been 
  inclined, 
  in 
  the 
  absence 
  of 
  proof, 
  however, 
  to 
  class 
  it 
  as 
  

   Jurassic 
  ; 
  but 
  certain 
  geologists. 
  Dr. 
  Peale, 
  Mr. 
  Howell, 
  and 
  Dr. 
  New- 
  

   berry, 
  have 
  found 
  Cretaceous 
  fossils, 
  or 
  what 
  are 
  recognized 
  as 
  such, 
  in 
  

   a 
  series 
  of 
  sandstones 
  that 
  come 
  in 
  at 
  the 
  base 
  of 
  the 
  marls, 
  and 
  into 
  

   which 
  the 
  marls 
  grade. 
  If 
  we 
  include 
  these 
  formations 
  in 
  the 
  Lower 
  

   Cretaceous 
  down 
  to 
  the 
  horizon 
  in 
  which 
  these 
  fossils 
  were 
  found, 
  that 
  

   is 
  from 
  400 
  to 
  600 
  feet 
  below 
  the 
  top 
  of 
  the 
  Dakota 
  Sandstones, 
  it 
  seems 
  

   that 
  we 
  will 
  have 
  to 
  include 
  in 
  the 
  Cretaceous 
  section 
  the 
  entire 
  group 
  

   of 
  marls 
  and 
  sandstones. 
  These 
  occur 
  here, 
  without 
  a 
  break, 
  to 
  the 
  

   thickness, 
  by 
  barometric 
  measurement, 
  of 
  600 
  feet. 
  This 
  gives 
  a 
  thick- 
  

   ness 
  of 
  at 
  least 
  800 
  feet 
  of 
  Lower 
  Cretaceous 
  strata. 
  I 
  prefer 
  to 
  

   divide 
  this 
  into 
  two 
  parts, 
  for 
  convenience 
  of 
  description 
  as 
  well 
  as 
  map- 
  

   ping. 
  The 
  upper 
  part 
  always 
  forms 
  a 
  plain 
  floor 
  or 
  the 
  upper 
  stratum 
  

   of 
  a 
  table-land, 
  and 
  the 
  broken 
  faces 
  give 
  universally 
  an 
  escarpment- 
  

   line, 
  while 
  the 
  lower 
  and 
  softer 
  group 
  outcrops 
  on 
  a 
  gentle 
  declivity 
  or 
  is 
  

   hidden 
  beneath 
  the 
  debris 
  of 
  the 
  talus. 
  Group 
  12 
  consists 
  of 
  brownish 
  

   and 
  purplish 
  laminated 
  sandstones, 
  generally 
  less 
  than 
  200 
  feet 
  in 
  thick- 
  

   ness. 
  This 
  is 
  the 
  fossil-bone 
  bed 
  of 
  Dr. 
  Newberry,* 
  which 
  is 
  thought 
  by 
  

   him 
  to 
  be 
  Triassic. 
  Group 
  13 
  is 
  the 
  well-marked 
  bed 
  of 
  massive 
  white 
  

   and 
  pinkish 
  sandstone. 
  This 
  is 
  succeeded 
  by 
  a 
  laminated 
  series, 
  and 
  

   this 
  by 
  red 
  sandstones. 
  The 
  more 
  important 
  parts 
  of 
  the 
  section 
  will 
  be 
  

   given 
  in 
  detail 
  farther 
  on. 
  

  

  * 
  Expedition 
  to 
  the 
  junction 
  of 
  Grand 
  and 
  Green 
  Rivers, 
  Capt. 
  J. 
  N. 
  Macomb, 
  1859 
  ; 
  

   page 
  91. 
  

  

  