﻿204 
  H. 
  K 
  Gregory 
  — 
  Geologic 
  Sketch 
  of 
  

  

  Agassiz.* 
  Steinmann,f 
  and 
  especially 
  Dereims4 
  have 
  by 
  their 
  

   recent 
  studies 
  extended 
  and 
  somewhat 
  modified 
  the 
  conclusions 
  

   reached 
  by 
  earlier 
  explorers. 
  The 
  publication 
  by 
  the 
  Bolivian 
  

   Ministerio 
  de 
  Justicia 
  y 
  Industria, 
  La 
  Paz, 
  1912, 
  of 
  a 
  Mapa 
  

   Geologico 
  de 
  Bolivia 
  by 
  Leonardo 
  Olmos, 
  serves 
  as 
  a 
  basis 
  for 
  

   further 
  Held 
  studies. 
  § 
  

  

  This 
  map 
  so 
  far 
  as 
  the 
  Titicaca 
  region 
  is 
  concerned 
  is 
  essen- 
  

   tially 
  a 
  reproduction 
  of 
  D'Orbigny's 
  Plate 
  VIII, 
  which 
  exhibits 
  

   Paleozoic 
  formations 
  as 
  bands 
  with 
  prevailing 
  northwest-south- 
  

   east 
  extensions. 
  The 
  periods 
  represented 
  west 
  of 
  the 
  Cor- 
  

   dillera 
  Real 
  are 
  in 
  succession: 
  Silurian, 
  forming 
  the 
  base 
  of 
  the 
  

   range; 
  Devonian, 
  in 
  a 
  broad 
  belt 
  forming 
  the 
  eastern 
  shore 
  of 
  

   Lago 
  Pequeno, 
  as 
  weil 
  as 
  the 
  peninsula 
  of 
  Taraco; 
  Carboniferous, 
  

   forming 
  the 
  west 
  shore 
  and 
  part 
  of 
  the 
  south 
  shore 
  of 
  Lago 
  

   Pequeno, 
  the 
  peninsulas 
  of 
  Achacachi 
  and 
  Copacabana, 
  and 
  all 
  

   the 
  islands. 
  ISTo 
  Cambrian 
  has 
  been 
  reported 
  from 
  southern 
  

   Pern 
  or 
  northern 
  Bolivia. 
  The 
  presence 
  of 
  Silurian 
  rests 
  on 
  

   ten 
  species 
  collected 
  by 
  D'Orbigny, 
  none 
  of 
  which 
  are 
  accepted 
  

   by 
  Salter 
  as 
  properly 
  determined 
  ; 
  five 
  Lower 
  (?) 
  Silurian 
  and 
  

   fourteen 
  Upper 
  Silurian 
  species, 
  mostly 
  from 
  the 
  Cordillera 
  

   Peal, 
  collected 
  by 
  Forbes 
  and 
  described 
  by 
  Salter; 
  Ordovician 
  

   graptolites 
  described 
  by 
  Steinmann 
  (1904); 
  Steinmann's 
  col- 
  

   lection 
  from 
  southern 
  Bolivia 
  described 
  by 
  Ulrich,|| 
  and 
  on 
  a 
  

   collection 
  of 
  graptolites 
  from 
  Santa 
  Domingo 
  presented 
  to 
  the 
  

   writer 
  by 
  Mr. 
  Collins, 
  manager 
  of 
  the 
  Inca 
  Mining 
  Co. 
  Dereims 
  

   also 
  reports 
  Silurian 
  at 
  several 
  localities 
  south 
  of 
  Lake 
  Titicaca. 
  

   The 
  presence 
  of 
  Devonian 
  in 
  the 
  Titicaca 
  region 
  was 
  first 
  demon- 
  

   strated 
  by 
  the 
  discovery 
  of 
  seven 
  species 
  by 
  D'Orbigny, 
  four 
  of 
  

   which 
  are 
  accepted 
  by 
  Salter 
  as 
  characteristic 
  of 
  that 
  era. 
  These 
  

   species, 
  including 
  three 
  additional 
  ones 
  collected 
  by 
  Forbes, 
  are 
  

   unlike 
  forms 
  found 
  elsewhere. 
  Dereims 
  found 
  Devonian 
  fos- 
  

   sils 
  in 
  brown 
  sandstone 
  and 
  shales 
  near 
  Lake 
  Titicaca, 
  a 
  collection 
  

   which 
  as 
  yet 
  has 
  not 
  been 
  reported 
  upon. 
  

  

  Carboniferous 
  strata 
  were 
  encountered 
  by 
  D'Orbigny 
  on 
  

   the 
  shores 
  and 
  islands 
  of 
  Lago 
  Pequeno, 
  where 
  brown 
  sand- 
  

   stone 
  is 
  underlain 
  by 
  compact 
  bluish 
  gray 
  " 
  mountain 
  lime- 
  

   stone." 
  The 
  fossils 
  collected 
  from 
  Amasa 
  and 
  Quebaya 
  islands 
  

   and 
  from 
  Yarbichambi 
  comprise 
  twenty 
  -live 
  species, 
  all 
  

   specifically 
  unlike 
  European 
  forms, 
  but 
  resembling, 
  according 
  

  

  *Agassiz 
  and 
  Garman, 
  Exploration 
  of 
  Lake 
  Titicaca, 
  Bull. 
  Mus. 
  Comp. 
  

   Zool., 
  Harv. 
  Coll., 
  vol. 
  iii, 
  1871-76, 
  fossils 
  described 
  by 
  Derby. 
  

  

  f 
  A 
  Sketch 
  of 
  the 
  Geology 
  of 
  South 
  America, 
  Am. 
  Naturalist, 
  1891, 
  pp. 
  

   855-860. 
  

  

  % 
  Excursiones 
  Cientificas 
  1901-04. 
  Anexo 
  de 
  la 
  Memoria 
  de 
  Gobierno 
  y 
  

   Fomento. 
  La 
  Paz, 
  1906. 
  

  

  §One 
  of 
  the 
  cross 
  sections 
  accompanying 
  this 
  map 
  is 
  confusing, 
  in 
  that 
  

   the 
  relations 
  between 
  Devonian 
  and 
  Carboniferous 
  in 
  the 
  Copacabana 
  

   area 
  are 
  not 
  in 
  harmony 
  with 
  the 
  surface 
  geology. 
  

  

  || 
  Paleozoische 
  Versteinerungen 
  aus 
  Bolivia, 
  Neues 
  Jahrbuch, 
  1892. 
  

  

  