﻿150 
  II. 
  E. 
  Gregory 
  — 
  La 
  Paz 
  (Bolivia) 
  Gorge. 
  

  

  in 
  response 
  to 
  seasonal 
  rainfall 
  would 
  produce 
  just 
  such 
  sedi- 
  

   ments 
  as 
  the 
  strata 
  under 
  discussion. 
  Temporary 
  lakes, 
  — 
  

   annual 
  or 
  lasting 
  for 
  decades, 
  — 
  are 
  normal 
  features 
  of 
  such 
  a 
  

   piedmont 
  flood 
  plain 
  and 
  are 
  ample 
  to 
  account 
  for 
  the 
  lenses 
  of 
  

   clay 
  and 
  the 
  thin, 
  short 
  bands 
  of 
  carbonaceous 
  material 
  occur- 
  

   ring 
  in 
  the 
  section. 
  

  

  The 
  geologic 
  history 
  of 
  the 
  La 
  Paz 
  gorge 
  can 
  not 
  be 
  written 
  

   on 
  the 
  basis 
  of 
  the 
  data 
  at 
  hand. 
  The 
  significance 
  of 
  the 
  inner 
  

   gravel 
  terrace 
  pointing 
  to 
  a 
  second, 
  or 
  perhaps 
  a 
  third, 
  cycle 
  of 
  

   filling 
  and 
  erosion, 
  the 
  conditions 
  under 
  which 
  the 
  remarkably 
  

   coarse 
  upper 
  beds 
  were 
  deposited, 
  the 
  character 
  of 
  the 
  floor 
  on 
  

   which 
  the 
  finer 
  sediments 
  were 
  laid 
  down, 
  the 
  extent 
  of 
  the 
  

   deposits 
  and 
  the 
  pre-glacial 
  history 
  of 
  the 
  La 
  Paz 
  river 
  itself, 
  

   are 
  problems 
  which 
  will 
  repay 
  detailed 
  physiographic 
  research. 
  

  

  