﻿THE 
  

  

  AMERICAN 
  JOURNAL 
  OF 
  SCIENCE 
  

  

  [FOURTH 
  SERIES.] 
  

  

  Art. 
  XXIII. 
  — 
  Geologic 
  Sketch 
  of 
  Titicaca 
  Island 
  and 
  Adjoin- 
  

   ing 
  Areas 
  • 
  by 
  Herbert 
  E. 
  Gregory.* 
  With 
  Plate 
  I. 
  

  

  Introduction. 
  

  

  The 
  great 
  Andean 
  Plateau 
  of 
  southern 
  Peru 
  and 
  northern 
  

   Bolivia, 
  the 
  " 
  altiplano," 
  has 
  a 
  width 
  in 
  the 
  Titicaca 
  region 
  of 
  

   approximately 
  50 
  miles. 
  Though 
  possessing 
  in 
  itself 
  relief 
  

   exceeding 
  a 
  thousand 
  feet, 
  its 
  jDlateau 
  features 
  are 
  well 
  brought 
  

   out 
  when 
  the 
  lofty 
  ranges 
  of 
  the 
  Cordillera 
  Real 
  and 
  the 
  

   Maritime 
  Andes, 
  between 
  which 
  it 
  is 
  hung, 
  are 
  taken 
  into 
  

   view. 
  The 
  bordering 
  range 
  on 
  the 
  northeast 
  maintains 
  a 
  

   height 
  of 
  over 
  17,000 
  feet 
  for 
  a 
  distance 
  of 
  200 
  miles 
  and 
  

   reaches 
  at 
  Sorata 
  (Illampu) 
  a 
  point 
  21,520 
  feet 
  (Conway) 
  above 
  

   sea 
  level. 
  The 
  western 
  border 
  of 
  the 
  plateau 
  is 
  a 
  wide 
  moun- 
  

   tainous 
  highland 
  crossed 
  by 
  the 
  railroad 
  at 
  14,666 
  feet, 
  and 
  

   maintaining 
  an 
  average 
  elevation 
  in 
  southern 
  Peru 
  of 
  nearly 
  

   11,000 
  feet. 
  As 
  shown 
  by 
  Bowman, 
  the 
  Maritime 
  Andes 
  is 
  a 
  

   dissected 
  peneplain 
  and 
  represents 
  a 
  mountain 
  range 
  which 
  

   may 
  have 
  exceeded 
  in 
  height 
  the 
  present 
  eastern 
  Cordillera. 
  

  

  Occupying 
  an 
  irregular 
  depression 
  in 
  the 
  high 
  plateau, 
  

   between 
  lat. 
  15° 
  20' 
  S. 
  and 
  16° 
  35 
  7 
  S. 
  lies 
  Lake 
  Titicaca 
  at 
  an 
  

   elevation 
  of 
  12,500 
  feet 
  above 
  sea 
  level. 
  The 
  lake 
  is 
  roughly 
  

   rectangular 
  in 
  shape, 
  one 
  hundred 
  miles 
  long, 
  and 
  with 
  an 
  

   extreme 
  breadth 
  of 
  thirty-eight 
  miles. 
  f 
  

  

  Its 
  superficial 
  area, 
  calculated 
  by 
  planimeter 
  from 
  the 
  best 
  

   available 
  maps, 
  is 
  approximately 
  1,000 
  square 
  miles, 
  and 
  the 
  

   length 
  of 
  the 
  shoreline 
  probably 
  exceeds 
  500 
  miles. 
  ;{; 
  Properly 
  

   speaking, 
  there 
  are 
  two 
  lakes, 
  connected 
  by 
  the 
  rock-walled 
  

   straits 
  of 
  Tiquina, 
  five-eighths 
  of 
  a 
  mile 
  wide. 
  The 
  lower 
  

  

  * 
  Geologist, 
  Peruvian 
  Expedition 
  of 
  1912. 
  

  

  f 
  The 
  figures 
  are 
  from 
  LeMaire. 
  No 
  complete 
  instrumental 
  survey 
  of 
  the 
  

   lake 
  has 
  yet 
  been 
  undertaken. 
  

  

  X 
  The 
  figures 
  given 
  by 
  Paz 
  Soldan 
  (270 
  miles) 
  and 
  by 
  certain 
  other 
  writers 
  

   are 
  manifestly 
  too 
  small. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XXXVI, 
  No. 
  213.— 
  September, 
  1913. 
  

   13 
  

  

  