﻿ENDLlCH.l 
  CONCLUSION. 
  207 
  

  

  Middle 
  Cretaceous 
  shales 
  as 
  wanting. 
  In 
  case 
  they 
  did 
  exist 
  there, 
  then 
  

   it 
  might 
  become 
  a 
  difficult 
  matter 
  to 
  draw 
  the 
  line 
  of 
  separation 
  between 
  

   Cretaceous 
  and 
  Post 
  Cretaceous. 
  

  

  VOLCANIC 
  EOCKS. 
  

  

  Volcanic 
  formations 
  are 
  but 
  very 
  sparingly 
  represented 
  in 
  the 
  district 
  

   of 
  whicli 
  this 
  chapter 
  treats. 
  Station 
  126, 
  on 
  the 
  headwaters 
  of 
  the 
  Ca- 
  

   nadian, 
  is 
  located 
  on 
  a 
  small 
  outcrop 
  of 
  trachyte, 
  a 
  remnant 
  of 
  the 
  for- 
  

   merly 
  extensive 
  mass 
  farther 
  southwest. 
  From 
  there 
  the 
  trachyte 
  

   flowed 
  down 
  upon 
  the 
  Post-Cretaceous 
  beds, 
  covering 
  a 
  large 
  portion 
  of 
  

   them. 
  Gradual 
  erosion, 
  however, 
  carried 
  away 
  the 
  volcanic 
  beds, 
  nnd 
  

   once 
  more 
  exj^osed 
  the 
  underlying 
  sandstones 
  and 
  shales, 
  save 
  at 
  such 
  

   places 
  where, 
  for 
  local 
  reasons, 
  small 
  portions 
  were 
  suffered 
  to 
  remain. 
  

   In 
  the 
  northern 
  region 
  of 
  the 
  area 
  dikes 
  traverse 
  the 
  sandstones 
  and 
  

   shales, 
  having 
  had 
  an 
  origin, 
  probably, 
  synchronous 
  with 
  those 
  of 
  the 
  

   Spanish 
  Peaks. 
  They 
  reach 
  into 
  the 
  Post-Cretaceous 
  group 
  but 
  for 
  a 
  

   short 
  distance 
  only. 
  Dikes 
  of 
  the 
  entire 
  region 
  have 
  been 
  described^in 
  

   Chapter 
  I, 
  and 
  the 
  same 
  characteristics 
  there 
  given, 
  the 
  same 
  metamor- 
  

   phosing 
  influences 
  quoted, 
  hold 
  good 
  wherever 
  they 
  occur 
  in 
  the 
  Lig- 
  

   nitic 
  group. 
  

  

  DRIFT. 
  

  

  'So 
  large 
  drift 
  areas 
  were 
  found 
  in 
  this 
  section 
  of 
  country. 
  If 
  we 
  ex- 
  

   clude 
  the 
  western 
  edge 
  of 
  Stonewall 
  Valley 
  and 
  its 
  southern 
  continua- 
  

   tion, 
  there 
  will 
  be 
  but 
  few 
  localities 
  left 
  where 
  drift 
  occurs. 
  The 
  jthys- 
  

   ical 
  character 
  of 
  the 
  rocks 
  composing 
  hills 
  and 
  bluffs 
  is 
  such 
  that 
  ero- 
  

   sion 
  by 
  Avater 
  will 
  be 
  productive 
  of 
  clay 
  and 
  finely 
  separated 
  detritus 
  

   rather 
  than 
  voluminous 
  drift. 
  Wherever 
  the 
  character 
  of 
  a 
  valley 
  has 
  

   peraiitted 
  it, 
  we 
  find 
  in 
  consequence 
  of 
  this 
  peculiarity 
  a 
  deposit 
  of 
  soil. 
  

   This 
  is 
  turned 
  to 
  good 
  account 
  at 
  some 
  places 
  on 
  the 
  Purgatorio 
  drain- 
  

   age, 
  where 
  farms, 
  worked 
  by 
  Mexicans, 
  testify 
  to 
  the 
  richness 
  of 
  the 
  

   alluvium. 
  Comparable 
  with 
  the 
  lower 
  San 
  Juan 
  drainage, 
  we 
  find 
  that 
  

   the 
  valleys 
  are 
  most 
  frequently 
  nari-ow, 
  with 
  steep 
  sides, 
  a 
  form 
  that 
  is 
  

   incident 
  to 
  the 
  ready 
  disintegration 
  of 
  the 
  slopes 
  inclosing 
  it. 
  

  

  CONCLUSION. 
  

  

  In 
  the 
  conclusion 
  I 
  propose 
  to 
  present 
  in 
  a 
  concise 
  manner 
  such 
  de- 
  

   ductions 
  as 
  may 
  have 
  been 
  made 
  from 
  the 
  facts 
  observed 
  in 
  the 
  district 
  

   which 
  is 
  the 
  subject 
  of 
  this 
  report. 
  Inasmuch 
  as 
  both 
  the 
  districts 
  of 
  

   1873 
  and 
  1874 
  adjoin 
  the 
  one 
  treated 
  of 
  above, 
  it 
  is 
  possible 
  to 
  state 
  

   with 
  more 
  clearness 
  and 
  a 
  fuller 
  untlerstandiug, 
  the 
  purport 
  of 
  gener- 
  

   alizations 
  resulting 
  from 
  the 
  season's 
  observations. 
  Where 
  we 
  have 
  

   large 
  areas 
  of 
  one 
  single 
  formation 
  (as 
  is 
  the 
  case 
  in 
  this 
  instance) 
  it 
  

   becomes 
  a 
  matter 
  of 
  considerable 
  difdculty 
  to 
  arrive 
  at 
  definite 
  conclu- 
  

   sions 
  when 
  the 
  examination 
  of 
  such 
  areas 
  is 
  restricted 
  to 
  a 
  i)ortion 
  

   only. 
  In 
  order, 
  therefore, 
  to 
  complete 
  the 
  synopsis, 
  references 
  will 
  be 
  

   made 
  to 
  the 
  adjoining 
  districts 
  wherever 
  that 
  may 
  appear 
  desirable. 
  

   It 
  seems 
  best 
  to 
  discuss 
  the 
  characteristics 
  of 
  each 
  formation 
  in 
  a 
  suc- 
  

   cession 
  based 
  upon 
  their 
  geological 
  age, 
  thus 
  facilitating 
  allusions 
  to 
  

   one 
  or 
  the 
  o;her, 
  and 
  at 
  the 
  same 
  time 
  retaining 
  a 
  definite 
  classification. 
  

   I 
  regret 
  that 
  much 
  must 
  still 
  remain. 
  incomplete, 
  owing 
  to 
  the 
  want 
  of 
  in- 
  

   formation 
  as 
  regards 
  t!ie 
  n)ore 
  minute 
  details 
  of 
  many 
  localities. 
  Could 
  

   they 
  be 
  supplied, 
  the 
  ultimate 
  results 
  obtained 
  would 
  be 
  by 
  far 
  moresat- 
  

  

  