﻿Spencer 
  — 
  Devonian 
  Strata 
  in 
  Colorado. 
  125 
  

  

  Art. 
  XI. 
  — 
  Devonian 
  Strata 
  in 
  Colorado 
  ; 
  by 
  Arthur 
  C. 
  

  

  Spencer. 
  

  

  Early 
  recognition 
  of 
  Devonian. 
  — 
  The 
  presence 
  of 
  Devonian 
  

   strata 
  in 
  the 
  San 
  Juan 
  region 
  of 
  Southwestern 
  Colorado 
  was 
  

   announced 
  in 
  the 
  report 
  of 
  F. 
  M. 
  Endlich, 
  of 
  the 
  Hayden 
  

   Survey, 
  for 
  the 
  year 
  1874. 
  The 
  age 
  determination, 
  based 
  

   upon 
  a 
  small 
  collection 
  of 
  fossils, 
  was 
  made 
  by 
  F. 
  B. 
  Meek, 
  

   the 
  paleontologist 
  of 
  the 
  Hayden 
  Survey, 
  and 
  upon 
  the 
  evi- 
  

   dence 
  of 
  this 
  determination 
  the 
  geological 
  map 
  of 
  South- 
  

   western 
  Colorado 
  in 
  the 
  Hayden 
  atlas, 
  which 
  appeared 
  in 
  1877, 
  

   had 
  Devonian 
  areas 
  represented 
  upon 
  it. 
  This 
  work, 
  however, 
  

   has 
  been 
  either 
  lost 
  sight 
  of, 
  or 
  discredited 
  by 
  recent 
  writers 
  

   upon 
  the 
  geology 
  of 
  the 
  Rocky 
  Mountains. 
  In 
  his 
  paper 
  

   upon 
  " 
  Orographic 
  Movements 
  in 
  the 
  Rocky 
  Mountains," 
  

   S. 
  F. 
  Emmons* 
  indicates 
  that 
  of 
  the 
  areas 
  represented 
  upon 
  

   the 
  Hayden 
  map 
  as 
  Devonian 
  and 
  Carboniferous, 
  the 
  lower 
  

   part 
  is 
  known 
  to 
  be 
  Silurian, 
  though 
  the 
  facts 
  on 
  which 
  this 
  

   opinion 
  was 
  founded 
  are 
  not 
  given. 
  Again 
  in 
  a 
  paper 
  upon 
  

   "Orographic 
  and 
  Structural 
  Features 
  of 
  Rocky 
  Mountain 
  

   Geology," 
  R. 
  C. 
  Hillsf 
  states, 
  without 
  qualification, 
  that 
  there 
  

   are 
  no 
  recognizable 
  Devonian 
  sediments 
  between 
  the 
  Silurian 
  

   and 
  Carboniferous 
  in 
  the 
  San 
  Juan 
  region. 
  He, 
  however, 
  

   expresses 
  the 
  belief 
  that 
  Devonian 
  strata 
  may 
  yet 
  be 
  found 
  in 
  

   Southwestern 
  Colorado. 
  

  

  Further 
  information 
  concerning 
  the 
  strata 
  from 
  which 
  End- 
  

   lich 
  collected 
  the 
  fossils, 
  pronounced 
  by 
  Meek 
  to 
  be 
  Devonian, 
  

   has 
  recently 
  been 
  obtained 
  by 
  the 
  Geological 
  Survey 
  party 
  

   in 
  charge 
  of 
  Dr. 
  Whitman 
  Cross, 
  while 
  engaged 
  in 
  areal 
  

   mapping. 
  The 
  writer 
  was 
  a 
  member 
  of 
  the 
  party, 
  both 
  

   in 
  1897, 
  when 
  the 
  fossiliferous 
  limestones 
  were 
  found, 
  and 
  

   in 
  1898, 
  when 
  extensive 
  collections 
  were 
  made. 
  The 
  actual 
  

   localities 
  which 
  Endlich 
  mentions 
  have 
  not 
  been 
  revisited 
  

   as 
  yet, 
  but 
  all 
  the 
  forms 
  which 
  he 
  found, 
  together 
  with 
  

   many 
  others, 
  have 
  been 
  obtained 
  from 
  beds 
  in 
  the 
  Animas 
  

   valley, 
  which 
  are 
  evidently 
  connected 
  by 
  continuous 
  outcrop 
  

   with 
  the 
  Devonian 
  areas 
  mapped 
  by 
  Endlich. 
  

  

  The 
  fossils 
  which 
  Endlich 
  collected 
  have 
  been 
  preserved 
  in 
  

   the 
  National 
  Museum, 
  where 
  there 
  are, 
  also, 
  other 
  collections 
  

   from 
  beds 
  in 
  Central 
  Colorado 
  which 
  now 
  prove 
  to 
  be 
  related 
  

   to 
  those 
  of 
  the 
  San 
  Juan 
  region. 
  These 
  fossils 
  have 
  been 
  

   made 
  the 
  subject 
  of 
  careful 
  study 
  by 
  Dr. 
  Geo. 
  H. 
  Girty 
  of 
  the 
  

   U. 
  S. 
  Geological 
  Survey, 
  in 
  connection 
  with 
  the 
  determination 
  

   of 
  the 
  more 
  recent 
  collections. 
  The 
  result 
  of 
  Dr. 
  Girty's 
  

  

  * 
  Bull. 
  Geol. 
  Soc. 
  Am., 
  i, 
  p. 
  280. 
  f 
  Proc. 
  Sci. 
  Soc. 
  Colo., 
  iii, 
  p. 
  366. 
  

  

  