﻿190 
  II 
  E\ 
  Gregory 
  — 
  Geologic 
  Sketch 
  of 
  

  

  slime 
  78 
  ; 
  calcareous 
  mud, 
  a 
  trace; 
  organic 
  residue 
  18; 
  inde- 
  

   terminable 
  2. 
  This 
  sample 
  contained 
  the 
  same 
  minerals 
  as 
  

   were 
  found 
  in 
  Lago 
  Pequeno 
  and 
  differs 
  only 
  in 
  the 
  absence 
  

   of 
  lime 
  and 
  greater 
  abundance 
  of 
  globular 
  diatoms. 
  From 
  the 
  

   Huaicho 
  dredging 
  were 
  obtained 
  iron-coated 
  grains 
  of 
  quartz 
  

   " 
  resembling 
  the 
  sands 
  of 
  Sahara," 
  and 
  a 
  few 
  volcanic 
  frag- 
  

   ments. 
  Thoulet's 
  studies 
  show 
  that 
  the 
  deeper 
  parts 
  of 
  Titi- 
  

   caca 
  are 
  mantled 
  with 
  organic 
  materials, 
  chiefly 
  diatoms, 
  

   mingled 
  with 
  siliceous 
  and 
  calcareous 
  (in 
  Lago 
  Pequeno) 
  

   grains, 
  minute 
  fragments 
  of 
  minerals 
  either 
  wind-worn 
  or 
  vol- 
  

   canic, 
  rarely 
  meteoric. 
  Near 
  shore 
  sand, 
  plant 
  fragments, 
  and 
  

   small 
  shells 
  occur. 
  

  

  As 
  pointed 
  out 
  by 
  Agassiz, 
  the 
  peculiar 
  physical 
  conditions 
  

   of 
  the 
  lake 
  bottom 
  combined 
  with 
  high 
  elevation 
  and 
  high 
  

   temperature 
  of 
  water 
  should 
  tend 
  to 
  the 
  specialization 
  of 
  

   genera, 
  — 
  a 
  result 
  which 
  does 
  not 
  occur. 
  The 
  absence 
  of 
  unique 
  

   forms 
  and 
  the 
  poverty 
  of 
  species 
  are 
  remarkable. 
  The 
  two 
  

   genera 
  of 
  fish 
  and 
  the 
  mollusks 
  belong 
  to 
  widely 
  distributed 
  

   fresh-water 
  types. 
  The 
  Crustacea, 
  however, 
  have 
  for 
  their 
  

   nearest 
  relatives 
  marine 
  forms. 
  An 
  interesting 
  fact 
  pointed 
  

   out 
  by 
  Orton 
  is 
  that 
  one 
  of 
  the 
  fishes, 
  Trichomycterus 
  dispar, 
  

   occurs 
  also 
  in 
  the 
  Rimac 
  and 
  Guayaquil 
  rivers. 
  

  

  Lake 
  Water. 
  — 
  The 
  temperature 
  of 
  the 
  water, 
  under 
  the 
  

   influence 
  of 
  the 
  tropical 
  sun 
  and 
  of 
  the 
  rarefied 
  atmosphere, 
  is 
  

   remarkably 
  uniform 
  at 
  all 
  depths. 
  Of 
  thirty 
  -four 
  measure- 
  

   ments 
  made 
  by 
  Agassiz 
  in 
  which 
  the 
  temperature 
  of 
  the 
  water 
  

   at 
  the 
  bottom 
  was 
  compared 
  with 
  that 
  at 
  the 
  surface 
  and 
  that 
  

   of 
  the 
  air, 
  the 
  difference 
  between 
  bottom 
  and 
  surface 
  was 
  

   3°-4° 
  ; 
  the 
  bottom 
  temperature 
  being 
  54°-55° 
  (one 
  reading 
  

   51° 
  at 
  618 
  feet), 
  while 
  the 
  surface 
  temperatures 
  were 
  56°-57°. 
  

   Only 
  one 
  much 
  larger 
  range, 
  6*5°, 
  was 
  noted. 
  At 
  the 
  same 
  

   time 
  (January 
  1st 
  to 
  March 
  5th) 
  the 
  temperature 
  of 
  the 
  air 
  

   ranged 
  from 
  42°-44° 
  early 
  morning, 
  to 
  55°-63° 
  during 
  the 
  

   hottest 
  part 
  of 
  the 
  day 
  ; 
  extremes 
  of 
  47° 
  (cloudy) 
  and 
  67° 
  (very 
  

   bright) 
  were 
  observed. 
  

  

  The 
  mean 
  of 
  twenty-nine 
  records 
  taken 
  by 
  LeMaire 
  from 
  

   depths 
  between 
  11 
  feet 
  and 
  925 
  feet* 
  give 
  a 
  value 
  of 
  51 
  51° 
  F., 
  

   the 
  highest 
  reading 
  being 
  52*52° 
  F. 
  at 
  79 
  feet 
  and 
  607 
  feet, 
  and 
  

   the 
  lowest 
  48*92° 
  F. 
  at 
  11 
  feet, 
  49*64° 
  F. 
  at 
  160 
  feet, 
  and 
  

   49*46° 
  F. 
  at 
  740 
  feet. 
  A 
  grouping 
  of 
  LeMaire's 
  thermometric 
  

   observations 
  indicates 
  an 
  increase 
  from 
  surface 
  to 
  492 
  feet, 
  

   reaching 
  a 
  maximum 
  between 
  500 
  and 
  650 
  feet, 
  followed 
  by 
  

   a 
  slight 
  decrease 
  to 
  the 
  lowest 
  depths. 
  The 
  temperatures 
  of 
  

  

  *This 
  is 
  the 
  greatest 
  depth 
  obtained 
  by 
  soundings. 
  In 
  Marie 
  R. 
  Wright's 
  

   elaborate 
  book 
  "'Bolivia" 
  (1906) 
  is 
  an 
  illustration 
  of 
  the 
  loose 
  statements 
  

   frequently 
  found 
  in 
  print: 
  ''Its 
  depth 
  varies 
  from 
  250 
  feet 
  to 
  1500 
  feet, 
  

   and 
  there 
  are 
  places 
  where 
  it 
  is 
  unfathomable" 
  (p. 
  243). 
  

  

  