﻿PEALE.] 
  PALEOZOIC 
  EOCKS 
  CARBONIFEROUS. 
  75 
  

  

  mingling 
  of 
  Carboniferous 
  and 
  Permian 
  forms, 
  and 
  I 
  have 
  found 
  no 
  

   distinctively 
  Permian 
  fossils 
  in 
  the 
  lower 
  part. 
  The 
  same 
  condition 
  is 
  

   found 
  in 
  the 
  lower 
  part 
  of 
  the 
  Carboniferous 
  — 
  Subcarboniferons 
  and 
  

   Carboniferous 
  types 
  being 
  found 
  in 
  the 
  same 
  strata 
  north 
  of 
  Grand 
  

   Eiver. 
  Mr. 
  Marvine 
  assured 
  me, 
  in 
  1874, 
  that 
  the 
  gypsiferous 
  series 
  

   extended 
  down 
  into 
  the 
  Carboniferous. 
  

  

  Professor 
  White, 
  speaking 
  of 
  the 
  Plateau 
  Province, 
  is 
  inclined 
  to 
  

   think 
  that 
  the 
  whole 
  Carboniferous 
  age, 
  including 
  its 
  three 
  periods, 
  Sub- 
  

   carboniferous, 
  Carboniferous, 
  and 
  Permian, 
  is 
  represented 
  by 
  the 
  four 
  

   groups 
  recognized 
  in 
  the 
  Plateau 
  Province. 
  

  

  In 
  the 
  region 
  of 
  Eagle 
  Eiver 
  there 
  is 
  a 
  lithological 
  distinction 
  that 
  is 
  

   marked, 
  the 
  Subcarboniferous 
  consisting 
  of 
  limestones, 
  the 
  Carbonifer- 
  

   ous 
  of 
  sandstones 
  and 
  shales, 
  and 
  the 
  Permian, 
  by 
  calcareous 
  and 
  gyp- 
  

   siferous 
  beds, 
  although 
  it 
  is 
  difficult 
  to 
  say 
  where 
  the 
  lines 
  of 
  separation 
  

   are. 
  It 
  is 
  also 
  impossible 
  to 
  correlate 
  the 
  section 
  with 
  those 
  made 
  

   farther 
  westward 
  where 
  limestones 
  prevail. 
  It 
  may 
  be 
  that 
  the 
  upper 
  

   limestone 
  of 
  the 
  Aubrey 
  is 
  wanting 
  East, 
  and 
  that 
  the 
  gypsiferous 
  beds 
  

   below 
  it 
  are 
  equivalent, 
  in 
  part 
  at 
  least, 
  with 
  a 
  portion 
  of 
  the 
  gypsum 
  

   series 
  of 
  Eagle 
  Eiver. 
  

  

  Over 
  the 
  greater 
  part 
  of 
  our 
  district 
  the 
  Upper 
  Carboniferous 
  rocks 
  

   are 
  wanting. 
  During 
  Upper 
  Carboniferous 
  times 
  there 
  was 
  a 
  shore-line 
  

   to 
  the 
  west 
  of 
  station 
  33 
  ; 
  what 
  the 
  other 
  boundaries 
  of 
  the 
  ancient 
  sea 
  

   were, 
  it 
  is 
  impossible 
  to 
  say. 
  On 
  Eagle 
  Eiver 
  the 
  characters 
  of 
  the 
  

   strata 
  through 
  the 
  Coal-Measures 
  and 
  into 
  the 
  Permo-Carboniferous 
  in- 
  

   dicate 
  that 
  there 
  was 
  marshy 
  land 
  of 
  considerable 
  persistence 
  in 
  that 
  

   neighborhood. 
  In 
  the 
  Park 
  range 
  again, 
  the 
  strata 
  indicate 
  shallow 
  

   waters 
  and 
  a 
  shore-line 
  not 
  far 
  to 
  the 
  westward. 
  The 
  area, 
  therefore, 
  

   must 
  have 
  been 
  of 
  considerable 
  size. 
  As 
  we 
  go 
  to 
  the 
  north 
  and 
  west- 
  

   ward, 
  limestones 
  are 
  more 
  abundant, 
  evidencing 
  the 
  existence 
  of 
  an 
  ex- 
  

   tensive 
  sea, 
  of 
  considerable 
  depth. 
  East 
  of 
  the 
  Eocky 
  Mountains, 
  the 
  

   facts 
  point 
  to 
  the 
  same 
  state 
  of 
  things. 
  The 
  paleozoic 
  continent 
  was 
  

   mainly 
  composed 
  of 
  Archaean 
  rocks 
  which 
  were 
  gradually 
  subsiding, 
  and 
  

   in 
  Triassic 
  times 
  were 
  probably 
  altogether 
  under 
  water 
  in 
  our 
  district. 
  

   As 
  we 
  have 
  seen 
  already, 
  fragmental 
  rocks 
  derived 
  from 
  the 
  erosion 
  of 
  

   the 
  Archaean 
  continent 
  or 
  islands 
  were 
  formed 
  over 
  our 
  district. 
  The 
  

   laminated 
  and 
  conglomeritic 
  conditions 
  of 
  the 
  strata 
  prove 
  that 
  there 
  

   was 
  a 
  general 
  subsidence. 
  Judging 
  from 
  the 
  thickness 
  of 
  the 
  beds, 
  from 
  

   the 
  lowest 
  limestone 
  we 
  discovered, 
  to 
  the 
  base 
  of 
  the 
  Triassic, 
  this 
  sub- 
  

   sidence, 
  during 
  Carboniferous 
  times, 
  was 
  at 
  least 
  4,000 
  feet. 
  It 
  was 
  prob- 
  

   ably 
  more, 
  for 
  it 
  is 
  not 
  likely 
  that 
  the 
  limestone 
  referred 
  to 
  was 
  the 
  

   lowest 
  bed 
  of 
  the 
  Carboniferous. 
  The 
  rate 
  of 
  subsidence 
  was 
  probably 
  

   not 
  not 
  much, 
  if 
  any, 
  greater 
  than 
  the 
  rate 
  of 
  deposition 
  of 
  the 
  strata. 
  

  

  In 
  the 
  Elk 
  Mountains 
  we 
  find 
  a 
  considerable 
  thickness 
  of 
  Carbonifer- 
  

   ous 
  limestones. 
  Some 
  of 
  the 
  fossils 
  obtained 
  by 
  Mr. 
  Holmes 
  from 
  the 
  

   lower 
  layers 
  indicate 
  that 
  they 
  are 
  Subcarboniferous. 
  When 
  these 
  

   beds 
  were 
  formed, 
  therefore, 
  the 
  Elk 
  Mountains 
  were 
  beneath 
  the 
  level 
  

   of 
  the 
  sea, 
  and 
  there 
  must 
  have 
  been 
  a 
  shore-line 
  southwest 
  of 
  the 
  Elk 
  

   Mountains, 
  between 
  them 
  and 
  the 
  Grand 
  Canon 
  of 
  the 
  Gunnison, 
  for 
  in 
  

   the 
  latter 
  place 
  there 
  are 
  no 
  Carboniferous 
  strata 
  on 
  the 
  gneissic 
  rocks. 
  

   There 
  was, 
  then, 
  in 
  early 
  Carboniferous 
  times, 
  a 
  belt 
  of 
  land, 
  about 
  50 
  

   miles 
  in 
  width, 
  lying 
  between 
  the 
  present 
  position 
  of 
  the 
  Elk 
  Mountains 
  

   and 
  that 
  of 
  the 
  Sierra 
  la 
  Sal. 
  

  

  In 
  Silurian 
  ages 
  the 
  area 
  was 
  probably 
  larger. 
  We 
  cannot 
  say 
  posi- 
  

   tively 
  that 
  Silurian 
  strata 
  are 
  seen 
  in 
  the 
  Elk 
  Mountains, 
  nor 
  how 
  far 
  

   westward 
  we 
  must 
  go 
  to 
  find 
  the 
  formation. 
  In 
  the 
  Park 
  range, 
  in 
  1873, 
  

   I 
  found 
  Silurian 
  fossils, 
  and, 
  north 
  of 
  Grand 
  Eiver, 
  Mr. 
  Marvine, 
  the 
  fol- 
  

  

  