﻿KNDLicH.] 
  SAN 
  JUAN 
  EEGION— 
  TERTIARY. 
  189 
  

  

  were 
  ejected, 
  we 
  would 
  infer 
  that 
  the 
  plateau 
  then 
  existing 
  was, 
  to 
  a 
  large 
  

   extent, 
  covered 
  with 
  trachorheites. 
  From 
  the 
  evidence 
  furnished 
  by 
  sta- 
  

   tion 
  63, 
  it 
  would 
  appear 
  that 
  then 
  already 
  the 
  dip 
  of 
  the 
  sedimentary 
  

   strata 
  was 
  a 
  westerly 
  one. 
  After 
  the 
  flows 
  of 
  lava 
  had 
  covered 
  the 
  pla- 
  

   teau, 
  that 
  period 
  followed 
  during 
  which 
  the 
  trachytic 
  conglomerate 
  was 
  

   formed. 
  This 
  would 
  have 
  accumulated, 
  as 
  usual, 
  in 
  varying 
  thickness, 
  

   at 
  places 
  best 
  adapted 
  for 
  its 
  reception. 
  Subsequent 
  to 
  the 
  trachytic 
  

   flows 
  were 
  the 
  basaltic 
  ones, 
  and 
  we 
  would 
  have 
  but 
  a 
  repetition 
  of 
  the 
  

   succession 
  observed 
  at 
  the 
  southern 
  end 
  of 
  the 
  Sawatch 
  Eange. 
  Could 
  

   this 
  be 
  established, 
  the 
  interesting 
  question 
  as 
  to 
  the 
  former 
  connection 
  

   of 
  the 
  San 
  Luis 
  basalts 
  with 
  those 
  of 
  Tierra 
  Amarilla 
  would 
  be 
  solved. 
  I 
  

   am 
  inclined 
  to 
  accept 
  such 
  connection, 
  and 
  hold 
  that 
  it 
  was 
  eventually 
  

   broken 
  by 
  the 
  gradual 
  elevation 
  of 
  the 
  Sawatch 
  Eange. 
  This 
  breaking 
  

   of 
  superficial 
  strata 
  produced 
  cracks 
  and 
  fissures 
  which 
  were 
  utilized 
  by 
  

   water, 
  and 
  thus 
  the 
  process 
  of 
  erosion 
  and 
  transportation 
  was 
  greatly 
  

   augmented. 
  How 
  far 
  south 
  the 
  volcanic 
  capping 
  may 
  have 
  extended 
  over 
  

   the 
  ancient 
  plateau 
  I 
  am 
  unable 
  to 
  say, 
  but 
  I 
  do 
  not 
  think 
  that 
  it 
  was 
  for 
  

   any 
  great 
  distance. 
  Under 
  the 
  basalt 
  of 
  the 
  Cerro 
  del 
  Navajo 
  we 
  find 
  

   no 
  trachyte. 
  It 
  is 
  true 
  that 
  this 
  may 
  be 
  owing 
  to 
  erosion 
  during 
  the 
  

   post-trachytic 
  period 
  before 
  the 
  eruption 
  of 
  basalt, 
  but 
  this 
  view 
  is 
  not 
  

   warranted 
  by 
  the 
  observations 
  made. 
  Most 
  likely 
  the 
  trachyte 
  " 
  pinched 
  

   out" 
  gradually 
  as 
  it 
  extended 
  southward, 
  and 
  the 
  subsequently 
  ejected 
  

   basalt 
  flowed 
  beyond 
  the 
  limits 
  of 
  the 
  former. 
  

  

  TERTIARY. 
  

  

  Quite 
  an 
  extensive 
  area 
  is 
  covered 
  by 
  Tertiary 
  beds 
  in 
  the 
  district 
  

   of 
  1875. 
  It 
  has 
  been 
  mentioned 
  above 
  that 
  the 
  Puerco 
  marls 
  of 
  Cope* 
  

   form 
  there 
  the 
  lowest 
  member 
  of 
  the 
  Wasatch 
  group. 
  They 
  were 
  best 
  

   observed 
  on 
  the 
  Lower 
  Animas. 
  A 
  section 
  (Section 
  XIII) 
  running 
  along 
  

   the 
  eastern 
  side 
  of 
  the 
  Animas 
  will 
  demonstrate 
  the 
  succession 
  of 
  the 
  

   strata. 
  Resting 
  upon 
  the 
  sandstones 
  of 
  the 
  Dakota 
  group 
  («) 
  we 
  find 
  

   the 
  Colorado 
  shales 
  (&). 
  They 
  are 
  covered 
  in 
  turn 
  by 
  a 
  series 
  of 
  shales 
  

   and 
  sandstones 
  (c) 
  belonging 
  to 
  the 
  Fox 
  Hills. 
  This 
  group 
  is 
  closed 
  by 
  

   a 
  heavy 
  bed 
  of 
  yellow 
  sandstone 
  (d). 
  Above 
  that 
  follow 
  1,000 
  to 
  

   1,200 
  feet 
  of 
  variegated 
  shales 
  and 
  marls 
  (e), 
  the 
  Puerco 
  marls. 
  At 
  the 
  

   base 
  they 
  are 
  a 
  muddy 
  green, 
  changing 
  into 
  yellow 
  or 
  almost 
  blue. 
  

   Farther 
  up, 
  pink, 
  pale 
  orange, 
  lilac, 
  and 
  reddish 
  colors 
  predominate, 
  

   i^aried 
  by 
  interstrata 
  of 
  white 
  or 
  light 
  yellow. 
  Thin 
  beds 
  of 
  sand- 
  

   i 
  ^one 
  merely 
  of 
  local 
  occurrence, 
  however, 
  separate 
  these 
  beds 
  ; 
  not, 
  

   1 
  rming 
  definite, 
  recognizable 
  horizons. 
  I 
  have 
  no 
  doubt 
  tha^ 
  this 
  

   g 
  oup, 
  thoroughly 
  characteristic 
  in 
  its 
  physical 
  features 
  at 
  least, 
  is 
  

   the 
  same 
  one 
  which 
  Cope 
  found 
  in 
  New 
  Mexico 
  and 
  of 
  which 
  he 
  says:t 
  

   " 
  The 
  discovery 
  of 
  the 
  variegated 
  marls 
  was 
  one 
  of 
  no 
  little 
  interest 
  to 
  

   tht 
  writer, 
  inasmuch 
  as 
  I 
  had 
  made 
  special 
  eflbrts 
  to 
  find 
  Eocene 
  beds 
  

  

  int 
  lis 
  region, 
  and 
  they 
  were 
  now 
  crowned 
  with 
  success;" 
  "thethick- 
  

  

  nest 
  of 
  the 
  strata 
  exhibited 
  in 
  the 
  walls 
  of 
  the 
  Caiioucita 
  de 
  los 
  Vegas 
  I 
  

  

  estimated 
  at 
  1,200 
  feet;" 
  " 
  the 
  red 
  and 
  grey 
  marls, 
  with 
  alternating 
  

  

  beds 
  of 
  white 
  and 
  yellowish 
  sandstone, 
  appear 
  on 
  their 
  summits 
  (of 
  the 
  

  

  red 
  sandstones) 
  and 
  form 
  amass 
  of 
  bad-land 
  blufls 
  from 
  600 
  to 
  1,000 
  

  

  feet 
  elevation." 
  In 
  my 
  field-notes 
  for 
  1875, 
  I 
  state 
  : 
  " 
  The 
  sandstones, 
  

  

  'Annual 
  Report 
  of 
  Explorations 
  and 
  Surveys 
  West 
  of 
  the 
  One 
  Hundredth 
  Meridian, 
  

   Appendix 
  44, 
  1875, 
  p. 
  88. 
  

  

  t 
  Anr 
  al 
  Report 
  of 
  Explorations 
  and 
  Surveys 
  West 
  of 
  the 
  One 
  Hundredth 
  Meridian, 
  

   Appenc 
  c 
  44, 
  1875, 
  p. 
  89. 
  

  

  