﻿ENDLicH.] 
  SANGRE 
  DE 
  CRISTO 
  — 
  DRIFT. 
  137 
  

  

  East 
  of 
  the 
  drift 
  of 
  station 
  118 
  the 
  metamorphic 
  granite 
  crops 
  out 
  paral- 
  

   lel 
  to 
  the 
  former. 
  The 
  Carboniferous 
  strata 
  have 
  evidently 
  been 
  either 
  worn 
  

   away 
  by 
  some 
  active 
  process 
  of 
  erosion 
  or 
  have 
  been 
  broken 
  off 
  during 
  

   their 
  upheaval. 
  Adjoining- 
  the 
  compact 
  drift 
  on 
  the 
  west 
  is 
  the 
  drift 
  of 
  

   San 
  Luis 
  Valley, 
  containing 
  near 
  the 
  edge 
  specimens 
  that 
  have 
  been 
  

   carried 
  thence 
  from 
  the 
  bluffs 
  iu 
  question, 
  but 
  they 
  do 
  not 
  extend 
  into 
  

   the 
  valley 
  for 
  any 
  distance. 
  It 
  seems 
  difficult 
  to 
  explain 
  the 
  origin 
  of 
  

   tbese 
  drift-bluffs. 
  Their 
  considerable 
  extent, 
  their 
  height, 
  and 
  their 
  

   relative 
  position 
  indicate 
  action 
  of 
  great 
  force. 
  No 
  attempt 
  at 
  distinct 
  

   stratification 
  was 
  observed, 
  and 
  from 
  the 
  nature 
  of 
  the 
  heterogeneous 
  

   arrangement 
  of 
  the 
  bowlders 
  it 
  seems 
  injprobable 
  that 
  they 
  should 
  owe 
  

   their 
  existence 
  to 
  the 
  agency 
  of 
  water 
  only. 
  The 
  only 
  explanation 
  I 
  

   can 
  offer 
  to 
  account 
  for 
  their 
  unique 
  character 
  (in 
  that 
  region) 
  is 
  that 
  

   they 
  are 
  the 
  result 
  of 
  deposition 
  by 
  moving 
  ice-fields, 
  by 
  glaciers, 
  to- 
  

   gether 
  with 
  water. 
  If 
  we 
  study 
  the 
  character 
  of 
  the 
  metamorphics 
  from 
  

   an 
  orographical 
  standpoint 
  we 
  will 
  find 
  that 
  their 
  outlines, 
  the 
  carving 
  

   they 
  exhibit 
  near 
  the 
  western 
  base 
  of 
  the 
  mountains, 
  indicate 
  glacial 
  

   erosion. 
  I 
  did 
  not 
  succeed 
  in 
  observing 
  striation, 
  or 
  any 
  definite 
  proof 
  

   for 
  this 
  assertion, 
  but 
  the 
  habitus 
  of 
  that 
  region 
  is 
  certainly 
  glacial. 
  

   Adding 
  to 
  this, 
  I 
  consider 
  the 
  disappearance 
  of 
  the 
  Carboniferous 
  strata 
  

   near 
  station 
  118 
  and 
  the 
  exposure 
  of 
  the 
  granite 
  as 
  circumstantial 
  evi- 
  

   dence 
  in 
  favor 
  of 
  the 
  acceptance 
  of 
  glaciers 
  in 
  accounting 
  for 
  the 
  exist- 
  

   ence 
  of 
  the 
  drilt-bluffs. 
  All 
  the 
  western 
  glaciers 
  in 
  the 
  district 
  surveyed 
  

   during 
  ]875 
  are 
  of 
  basaltic 
  or 
  post 
  basaltic 
  age, 
  more 
  frequently 
  the 
  latter, 
  

   so 
  that 
  it 
  would 
  seem 
  that 
  after 
  the 
  enormous 
  moraines 
  in 
  question 
  had 
  

   been 
  dejjosited 
  another 
  flow 
  took 
  place 
  here 
  and 
  covered 
  a 
  portion 
  of 
  

   them. 
  I 
  doubt 
  not 
  that 
  these 
  bluffs 
  afford 
  the 
  key 
  to 
  the 
  pre-glacial 
  or 
  

   earliest 
  glacial 
  history 
  of 
  San 
  Luis. 
  Valley, 
  but 
  as 
  very 
  careful 
  examina- 
  

   tions 
  and 
  detail 
  study 
  would 
  be 
  required 
  to 
  arrive 
  at 
  any 
  correct 
  con- 
  

   clusions 
  such 
  as 
  we 
  were 
  not 
  able 
  to 
  make 
  during 
  our 
  survey, 
  I 
  can- 
  

   not 
  make 
  any 
  positive 
  assertions 
  accompanied 
  by 
  the 
  requisite 
  proof. 
  

   In 
  the 
  discussion 
  of 
  glacial 
  phenomena 
  this 
  subject 
  will 
  bo 
  more 
  

   fully 
  treated 
  of. 
  I 
  do 
  not 
  consider 
  the 
  assertion 
  regarding 
  glaciers 
  

   as 
  the 
  moving 
  agents 
  proved, 
  but 
  it 
  is 
  an 
  explanation 
  that 
  can 
  be 
  sus- 
  

   tained 
  by 
  iacts, 
  which, 
  though 
  at 
  i)resent 
  but 
  impetfectly 
  collected, 
  

   may 
  some 
  day, 
  after 
  more 
  elaborate 
  examinations, 
  prove 
  to 
  be 
  con- 
  

   clusive. 
  It 
  is 
  possible 
  that 
  the 
  presence 
  of 
  this 
  enormous 
  secondary 
  

   deposit 
  niijy 
  point 
  to 
  the 
  inference 
  that 
  before 
  the 
  " 
  lake 
  period 
  " 
  a 
  large 
  

   portion 
  of 
  San 
  Luis 
  Valley 
  may 
  have 
  been 
  covered 
  by 
  a 
  glacier 
  — 
  may, 
  

   in 
  fact, 
  owe 
  the 
  details 
  of 
  its 
  present 
  topography 
  at 
  certain 
  localities 
  

   to 
  such 
  agency. 
  

  

  On 
  the 
  eastern 
  side 
  of 
  the 
  Sangre 
  de 
  Cristo 
  Eange, 
  the 
  drift-deposits 
  

   are 
  local 
  and 
  of 
  small 
  extent. 
  All 
  along 
  the 
  base 
  of 
  the 
  mount- 
  

   ains, 
  in 
  the 
  valiey 
  leading 
  from 
  Costilla 
  Peak 
  northward 
  toward 
  the 
  

   Spanish 
  Peaks, 
  the 
  metamorphic 
  rocks 
  and 
  Carboniferous 
  sandstone 
  

   bowlders 
  have 
  been 
  carried 
  down, 
  covering 
  the 
  western 
  edge 
  of 
  the 
  

   valley 
  completely. 
  Flowing 
  water 
  and 
  perhaps 
  snow-slides 
  have 
  here 
  

   been 
  the 
  moviug 
  agents, 
  and 
  in 
  consequence 
  the 
  accumulation 
  of 
  the 
  

   drift 
  is 
  not 
  a 
  regular 
  one, 
  but 
  distributed 
  according 
  to 
  capability 
  of 
  

   the 
  streams. 
  Along 
  the 
  western 
  border 
  of 
  the 
  Gi^eenhoru 
  Mountaius 
  

   we 
  find 
  the 
  same 
  thing 
  occurring. 
  There, 
  too, 
  metamorphic 
  rocks 
  and 
  

   sandstones 
  (IMesozoic) 
  have 
  been 
  carried 
  down 
  and 
  deposited 
  p;iral!el 
  to 
  

   the 
  edge 
  of 
  the 
  mountains 
  and 
  water-courses. 
  This 
  is 
  a 
  phenomenon 
  

   so 
  common 
  at 
  the 
  base 
  of 
  the 
  mountains 
  in 
  the 
  entire 
  region, 
  that 
  it 
  

   scarcely 
  deserves 
  special 
  mention. 
  Only 
  in 
  so 
  far 
  is 
  it 
  of 
  importance, 
  

   as 
  in 
  some 
  instance 
  glaciers 
  have 
  had 
  an 
  influence 
  on 
  the 
  deposition, 
  

  

  