﻿164 
  EEPOKT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  leaving 
  the 
  eastward-sloping 
  plateau. 
  Higher 
  peaks, 
  as 
  those 
  upon 
  

   -which 
  the 
  above-cited 
  stations 
  were 
  located, 
  have 
  escaped 
  the 
  denuding 
  

   influence 
  of 
  the 
  glacier, 
  save 
  at 
  their 
  bases, 
  but 
  east 
  and 
  west 
  of 
  them, 
  

   the 
  entire 
  region 
  was 
  covered 
  with 
  the 
  moving 
  ice-fields. 
  In 
  accord- 
  

   ance 
  with 
  the 
  physical 
  character 
  of 
  the 
  conglomerate 
  underlying 
  the 
  

   trachyte, 
  it 
  has 
  readily 
  yielded 
  to 
  the 
  carving 
  action 
  of 
  the 
  water 
  and 
  

   ice, 
  and 
  precipitous 
  walls, 
  starting 
  at 
  the 
  point 
  where 
  the 
  protectingJ:ra- 
  

   chyte 
  has 
  been 
  worn 
  away, 
  and 
  inclosing 
  on 
  either 
  side 
  the 
  caiion, 
  

   give 
  testimony 
  of 
  the 
  long-continued 
  erosive 
  activity 
  of 
  the 
  glaciers. 
  

   It 
  seems 
  probable, 
  though 
  it 
  could 
  not 
  be 
  proved 
  without 
  examination 
  

   that 
  would 
  consume 
  more 
  time 
  than 
  we 
  could 
  spare, 
  that 
  some 
  of 
  the 
  

   glaciers 
  extended 
  down 
  to 
  the 
  edge 
  of 
  San 
  Luis 
  Valley. 
  The 
  shape 
  

   and 
  character 
  of 
  the 
  canons, 
  more 
  particularly, 
  and 
  the 
  transportation 
  

   of 
  material, 
  would 
  argue 
  for 
  this 
  assumption. 
  No 
  moraines 
  that 
  could 
  

   be 
  considered 
  characteristic 
  or 
  typical 
  were 
  found 
  outside 
  of 
  the 
  mount- 
  

   ains, 
  but 
  the 
  uniform 
  habitat 
  of 
  the 
  caiions 
  throughout 
  their 
  entire 
  

   length, 
  permit 
  a 
  view 
  of 
  that 
  kind 
  to 
  appear 
  probable. 
  In 
  Appendix 
  A, 
  

   the 
  glaciers 
  of 
  Southern 
  Colorado 
  are 
  discussed 
  more 
  at 
  length. 
  In 
  har- 
  

   mony 
  with 
  the 
  general 
  dip 
  of 
  the 
  volcanic 
  strata 
  of 
  the 
  eastern 
  slope 
  of 
  

   the 
  Sawatch 
  Eange, 
  we 
  find 
  here, 
  too, 
  an 
  inclination 
  toward 
  the 
  East. 
  

   It 
  becomes 
  very 
  evident 
  in 
  the 
  conglomerates. 
  At 
  the 
  heads 
  of 
  the 
  

   glacial 
  caiions 
  their 
  thickness 
  is 
  from 
  800 
  to 
  1,000 
  feet, 
  showing 
  slight 
  

   local 
  variations, 
  dependent 
  upon 
  the 
  facilities 
  for 
  deposition. 
  Twenty 
  

   miles 
  farther 
  east, 
  just 
  at 
  the 
  exit 
  of 
  the 
  Conejos 
  from 
  the 
  mountains, 
  

   the 
  npper 
  stratum 
  of 
  the 
  conglomerate 
  appears 
  in 
  the 
  bed 
  of 
  the 
  river 
  

   and 
  the 
  low 
  banks 
  immediately 
  adjoining. 
  Comparing 
  the 
  elevations 
  

   here, 
  and 
  at 
  the 
  beginning 
  of 
  the 
  basaltic 
  cap 
  vertically 
  above 
  it, 
  we 
  

   find 
  that 
  the 
  entire 
  trachytic 
  series 
  participates 
  in 
  this 
  dip, 
  as 
  well 
  as 
  

   the 
  superincumbent 
  basalt. 
  Although 
  the 
  conglomerate 
  in 
  these 
  caiions 
  

   is 
  essentially 
  the 
  same 
  as 
  that 
  on 
  South 
  Eiver, 
  we 
  find 
  no 
  evidence 
  of 
  

   the 
  picturesque 
  monuments 
  that 
  there 
  are 
  so 
  well 
  developed. 
  Cavities 
  

   and 
  caves 
  occur, 
  together 
  with 
  column-shaped 
  rocks, 
  the 
  products 
  of 
  

   erosion 
  by 
  water, 
  both 
  frozen 
  and 
  flowing. 
  In 
  a 
  rock 
  of 
  the 
  constitu- 
  

   tion 
  like 
  this 
  conglomerate, 
  frost 
  is 
  one 
  of 
  the 
  most 
  powerful 
  eroding 
  

   agents. 
  Water 
  perm,eates 
  the 
  entire 
  mass, 
  and 
  upon 
  being 
  expanded 
  

   by 
  freezing, 
  finds 
  but 
  little 
  resistance 
  in 
  the 
  loose 
  sandy 
  agglomeration. 
  

   Thus, 
  in 
  a 
  comparatively 
  short 
  time, 
  the 
  detail 
  features 
  ot 
  a 
  caiion-wall 
  

   or 
  precipice 
  can 
  be 
  altered 
  beyond 
  recognition. 
  Though 
  striking 
  forms, 
  

   produced 
  in 
  this 
  manner, 
  are 
  not 
  wanting 
  in 
  the 
  conglomerate 
  of 
  the 
  

   caiions, 
  they 
  cannot 
  compare 
  with 
  those 
  south 
  of 
  the 
  Eio 
  Grande. 
  In 
  

   a 
  region 
  so 
  high 
  as 
  this 
  one 
  is, 
  the 
  frosts 
  continue 
  into 
  that 
  period 
  that 
  

   we 
  call 
  summer, 
  and 
  begin 
  again 
  in 
  August 
  ; 
  it 
  is 
  therefore 
  not 
  surpris- 
  

   ing 
  that 
  we 
  should 
  find 
  all 
  evidences 
  of 
  striation 
  or 
  grooving, 
  as 
  pro- 
  

   duced 
  by 
  glaciers, 
  obliterated 
  here, 
  where 
  undoubtedly 
  large 
  masses 
  of 
  

   ice 
  at 
  one 
  time 
  descended 
  in 
  that 
  form 
  of 
  a 
  glacier 
  that 
  is 
  appropriately 
  

   termed 
  -^StUTzgletscher^^ 
  in 
  German. 
  It 
  is 
  simply 
  analogous 
  to 
  a 
  water- 
  ^ 
  

   fall 
  ; 
  instead 
  of 
  water 
  we 
  have 
  ice. 
  

  

  At 
  the 
  southern 
  end 
  of 
  the 
  Sawatch 
  Eange, 
  so 
  far 
  as 
  it 
  is 
  in 
  our 
  dis- 
  

   trict, 
  a 
  change 
  of 
  formations 
  takes 
  place. 
  Although 
  trachyte 
  remains 
  

   the 
  principal 
  rock, 
  so 
  far 
  as 
  area 
  is 
  concerned, 
  it 
  was 
  found 
  that 
  meta- 
  

   morphic 
  beds 
  crop 
  out 
  from 
  underneath 
  it. 
  At 
  places, 
  the 
  volcanic 
  beds, 
  

   without 
  any 
  appreciable 
  change 
  in 
  their 
  general 
  elevation, 
  become 
  thin- 
  

   ner. 
  This 
  is 
  due 
  to 
  the 
  fact 
  that, 
  at 
  the 
  time 
  of 
  the 
  immense 
  volcanic 
  

   eruptions 
  that 
  have 
  covered 
  the 
  region, 
  the 
  configuration 
  of 
  the 
  country 
  

   was 
  already 
  a 
  very 
  much 
  broken 
  one. 
  We 
  find 
  in 
  this 
  region 
  that 
  

   mountains 
  of 
  metamorphic 
  rocks 
  must 
  have 
  existed, 
  which 
  were 
  either 
  

  

  