﻿Titicaca 
  Island 
  and 
  Adjoining 
  Areas. 
  195 
  

  

  ancient 
  channel 
  was 
  blocked 
  by 
  alluvium 
  and 
  glacial 
  debris, 
  

   thus 
  isolating 
  the 
  present 
  Titicaca. 
  The 
  ancient 
  level 
  of 
  the 
  

   original 
  lake 
  was 
  not 
  much 
  above 
  the 
  present, 
  and 
  is 
  marked 
  

   on 
  the 
  rocks 
  at 
  the 
  straits 
  of 
  Tiquina. 
  Duenas* 
  expresses 
  the 
  

   view 
  that 
  ancient 
  Titicaca 
  may 
  have 
  extended 
  into 
  the 
  Depart- 
  

   ment 
  of 
  Cuzco. 
  These 
  views 
  are 
  only 
  less 
  extreme 
  than 
  the 
  

   conclusion 
  of 
  Ortonf 
  that 
  the 
  " 
  depression 
  holding 
  Lake 
  Titi- 
  

   caca 
  is 
  apparently 
  a 
  volcanic 
  basin; 
  fragments 
  of 
  lava, 
  porphyry, 
  

   and 
  jasper 
  are 
  scattered 
  around 
  and 
  towers 
  of 
  igneous 
  rock 
  

   protrude 
  through 
  the 
  sedimentary 
  strata." 
  

  

  It 
  will 
  be 
  noted 
  that 
  the 
  conclusions 
  of 
  Le 
  Maire, 
  Posnansky, 
  

   and 
  others 
  rest 
  on 
  the 
  assumption 
  that 
  the 
  hypothetical 
  Titicaca 
  

   had 
  its 
  outlet 
  through 
  the 
  La 
  Paz 
  canyon, 
  an 
  assumption 
  neg- 
  

   atived 
  by 
  the 
  fact 
  that 
  the 
  deposits 
  at 
  La 
  Paz 
  are 
  of 
  later 
  date 
  

   than 
  the 
  lake 
  basin, 
  and 
  the 
  gorge 
  itself 
  is 
  in 
  large 
  part 
  post- 
  

   glacial 
  and 
  recent. 
  The 
  existence 
  of 
  the 
  hypothetical 
  u 
  Rio 
  

   Titicaca" 
  of 
  Zundt, 
  flowing 
  in 
  a 
  wide 
  valley 
  or 
  canyon 
  sunk 
  

   1000 
  feet 
  below 
  the 
  altiplano, 
  is 
  supported 
  by 
  no 
  evidence 
  

   from 
  the 
  lake 
  bed, 
  the 
  altiplano, 
  the 
  valley 
  of 
  La 
  Paz 
  river, 
  

   or 
  from 
  the 
  upper 
  part 
  of 
  the 
  supposed 
  valley 
  now 
  exposed 
  to 
  

   view 
  in 
  the 
  region 
  between 
  Huancani 
  and 
  Sicuani. 
  The 
  enor- 
  

   mous 
  lake 
  which 
  is 
  supposed 
  to 
  have 
  occupied 
  the 
  basin 
  between 
  

   the 
  two 
  Andean 
  ranges 
  is 
  believed 
  by 
  Posnansky 
  to 
  have 
  been 
  

   a 
  detached 
  portion 
  of 
  the 
  sea 
  elevated 
  12,000 
  to 
  13,000 
  feet 
  

   without 
  affecting 
  the 
  attitude 
  of 
  the 
  Mesozoic 
  strata. 
  Points 
  

   urged 
  by 
  Posnansky 
  in 
  favor 
  of 
  the 
  marine 
  origin 
  of 
  the 
  basin 
  

   are 
  deposits 
  of 
  salt 
  at 
  several 
  localities, 
  deposits 
  of 
  sediments 
  

   at 
  La 
  Paz 
  and 
  on 
  the 
  altiplano, 
  and 
  the 
  marine 
  affinities 
  of 
  

   the 
  fauna 
  of 
  the 
  lake. 
  The 
  first 
  two 
  points 
  have 
  little 
  signifi- 
  

   cance, 
  since 
  salt 
  is 
  a 
  constituent 
  of 
  the 
  country 
  rock, 
  and 
  the 
  

   sediments 
  at 
  La 
  Paz 
  are 
  river 
  deposits, 
  not 
  marine 
  or 
  even 
  

   wholly 
  lacustrine.^ 
  

  

  The 
  lake 
  fauna 
  exhibits 
  in 
  part 
  a 
  marine 
  facies, 
  but 
  is 
  not 
  

   necessarily 
  of 
  direct 
  marine 
  origin. 
  § 
  The 
  fish 
  are 
  fresh-water 
  

   forms, 
  with 
  marine 
  affinities 
  ; 
  the 
  mollusks, 
  copepods, 
  Daph- 
  

   nids, 
  and 
  ostracods 
  are 
  fresh-water 
  forms 
  ; 
  the 
  amphipods 
  pre- 
  

   sent 
  a 
  marine 
  aspect, 
  but 
  nothing 
  definite 
  may 
  be 
  said 
  of 
  their 
  

   origin. 
  The 
  only 
  true 
  marine 
  species 
  mentioned 
  by 
  Posnansky, 
  

   the 
  hippocampus, 
  is 
  not 
  found 
  in 
  the 
  extensive 
  collections 
  of 
  

   Agassiz 
  and 
  Le 
  Maire. 
  The 
  presence 
  of 
  this 
  species 
  in 
  the 
  

   lake, 
  a 
  conclusion 
  based 
  on 
  a 
  specimen 
  given 
  to 
  Posnansky 
  by 
  

   an 
  Indian 
  fisherman, 
  and 
  now 
  in 
  the 
  private 
  museum 
  of 
  the 
  

   collector, 
  requires 
  further 
  confirmation. 
  

  

  *Bol. 
  Cuerpo 
  de 
  Ing. 
  de 
  Min., 
  No. 
  53, 
  Lima, 
  1907, 
  p. 
  25. 
  

   f 
  The 
  Andes 
  and 
  the 
  Amazon, 
  1876. 
  

  

  X 
  See 
  Gregory: 
  The 
  La 
  Paz 
  Gorge, 
  this 
  Journal, 
  vol. 
  xxxvi, 
  pp. 
  141-150. 
  

   § 
  For 
  data 
  concerning 
  the 
  habitat 
  of 
  the 
  Titicaca 
  fauna, 
  I 
  am 
  indebted 
  to 
  

   my 
  colleague, 
  Professor 
  Petrnnkevitch. 
  

  

  