﻿364 
  EEPOET 
  UNITED 
  STATES 
  GEOLOGICAL 
  SUEVEY. 
  

  

  summit 
  which 
  rises 
  within 
  25 
  feet 
  of 
  this 
  one, 
  although 
  the 
  greater 
  

   sharpness 
  of 
  some 
  other 
  points 
  would 
  naturally 
  lead 
  the 
  observer 
  to 
  be- 
  

   lieve 
  them 
  at 
  least 
  as 
  high. 
  

  

  The 
  altitude 
  of 
  the 
  Mesa 
  Verde 
  ranges 
  from 
  6,500 
  feet 
  on 
  the 
  south- 
  

   ern 
  edge 
  to 
  8,500 
  on 
  the 
  northern, 
  it 
  being 
  a 
  little 
  lower 
  in 
  its 
  center 
  

   than 
  on 
  the 
  margin. 
  

  

  Pastora 
  Peak, 
  in 
  the 
  Carrisos, 
  is 
  very 
  little 
  higher 
  than 
  several 
  other 
  

   summits 
  in 
  the 
  mass, 
  but 
  is 
  slightly 
  more 
  prominent 
  than 
  any 
  other 
  one, 
  

   and 
  would 
  be 
  chosen 
  as 
  the 
  culminating 
  point 
  as 
  seen 
  from 
  either 
  side. 
  

  

  I 
  have 
  taken 
  several 
  angles 
  of 
  elevation 
  and 
  depression 
  at 
  the 
  

   "Needles," 
  south 
  of 
  the 
  San 
  Juan, 
  in 
  ISTew 
  Mexico 
  and 
  beyond 
  our 
  dis- 
  

   trict. 
  My 
  distances 
  were 
  so 
  great 
  that 
  the 
  results 
  have 
  a 
  considerable 
  

   range, 
  but 
  a 
  mean 
  of 
  what 
  seem 
  to 
  be 
  the 
  best 
  results 
  give 
  a 
  height 
  to 
  

   these 
  pinnacles 
  of 
  1,680 
  feet 
  above 
  the 
  level 
  plain. 
  These 
  needles, 
  stand- 
  

   ing 
  out 
  sheer 
  and 
  alone 
  from 
  the 
  plains, 
  make 
  a 
  wonderful 
  topograph- 
  

   ical 
  feature, 
  distinctly 
  seen 
  for 
  a 
  hundred 
  and 
  more 
  miles, 
  the 
  black 
  rock 
  

   of 
  which 
  they 
  are 
  composed 
  standing 
  out 
  with 
  peculiar 
  distinctness 
  

   against 
  the 
  dull 
  brown 
  of 
  the 
  plains. 
  Mr. 
  Holmes 
  made 
  several 
  sketches 
  

   of 
  the 
  group, 
  one 
  of 
  which 
  I 
  give 
  herewith, 
  showing 
  very 
  clearly 
  its 
  size 
  

   and 
  prominence. 
  (Plate 
  LIV.) 
  

  

  In 
  closing 
  my 
  discussion 
  of 
  altitudes, 
  I 
  give 
  a 
  table 
  of 
  fall, 
  total 
  and 
  

   per 
  mile, 
  of 
  the 
  principal 
  streams 
  and 
  gulches, 
  commencing 
  in 
  case 
  of 
  

   the 
  Mancos 
  and 
  La 
  Plata 
  at 
  their 
  exit 
  from 
  the 
  mountains. 
  

  

  stream. 
  

  

  Total 
  fall. 
  

  

  Fall 
  per 
  

   mile. 
  

  

  

  Feet. 
  

   1,000 
  

   3,300 
  

   4,200 
  

   2,000 
  

   2,450 
  

   2,500 
  

   900 
  

  

  Feet. 
  

   11 
  

  

  

  68 
  

  

  

  64 
  

  

  

  31 
  

  

  

  44 
  

  

  

  42 
  

  

  

  

  90 
  

  

  

  

  

  In 
  pursuing 
  this 
  work 
  I 
  have 
  employed 
  principally 
  a 
  plane-table 
  sys- 
  

   tem, 
  with 
  a 
  simple 
  portable 
  form 
  of 
  instrument, 
  constructed 
  under 
  the 
  

   direction 
  of 
  Prof. 
  Thomjison. 
  

  

  The 
  instrument 
  is 
  of 
  very 
  simple 
  construction, 
  and 
  entails 
  very 
  little 
  

   extra 
  carrying 
  upon 
  the 
  topographer. 
  The 
  table 
  itself 
  is 
  constructed, 
  

   like 
  a 
  form 
  of 
  field 
  writing-desk 
  in 
  common 
  use, 
  of 
  narrow 
  strips 
  of 
  wood, 
  

   firmly 
  cemented 
  to 
  heavy 
  face 
  of 
  cloth, 
  so 
  that 
  it 
  will 
  roll 
  up 
  into 
  a 
  

   compact 
  cylindrical 
  form 
  for 
  carrying, 
  and 
  spread 
  out 
  is 
  secured 
  by 
  

   cross-pieces 
  on 
  the 
  back, 
  giving 
  a 
  firm, 
  smooth 
  surface 
  on 
  the 
  covered 
  

   side. 
  This 
  table-top 
  is 
  made 
  to 
  set 
  upon 
  the 
  tripod 
  of 
  the 
  gradieuter 
  

   (our 
  instrument 
  for 
  angle 
  measurement) 
  and 
  to 
  clamp 
  firmly 
  in 
  place. 
  

  

  The 
  alidade 
  is 
  a 
  simple 
  rule 
  of 
  wood 
  or 
  metal 
  Avith 
  raised 
  sights, 
  which 
  

   in 
  carrying 
  rolls 
  in 
  with 
  the 
  table 
  and 
  paper, 
  entailing 
  only 
  the 
  extra 
  

   bulk 
  of 
  a 
  canvas 
  bag 
  two 
  feet 
  long 
  aud 
  five 
  inches 
  in 
  diameter 
  to 
  give 
  

   the 
  topographer 
  a 
  complete 
  plane-table 
  outfit. 
  The 
  method 
  of 
  working 
  

   must 
  of 
  course 
  be 
  almost 
  entirely 
  of 
  intersections, 
  since 
  the 
  distances 
  

   are 
  so 
  great 
  as 
  to 
  render 
  actual 
  measurements 
  ordinarily 
  impossible. 
  

  

  Unwilling 
  to 
  trust 
  the 
  accuracy 
  of 
  this 
  crude 
  instrument, 
  I 
  have 
  made 
  

   from 
  each 
  station 
  separate 
  topographical 
  sketches, 
  and 
  employed 
  the 
  

   usual 
  vis 
  a 
  ins 
  system 
  of 
  this 
  survey. 
  Had 
  I 
  known, 
  however, 
  in 
  the 
  

   field 
  the 
  accuracy 
  of 
  the 
  plane-table 
  locations 
  as 
  they 
  were 
  checked 
  in 
  

  

  