﻿Hatcher 
  — 
  Sedimentary 
  Rocks 
  of 
  Southern 
  Patagonia. 
  89 
  

  

  them 
  the 
  Mayer 
  River 
  beds, 
  from 
  the 
  name 
  of 
  the 
  river 
  in 
  

   the 
  bluffs 
  of 
  which 
  they 
  were 
  found. 
  The 
  localities 
  where 
  

   they 
  may 
  be 
  observed 
  were 
  described 
  in 
  ray 
  first 
  paper, 
  and 
  it 
  

   is 
  only 
  necessary 
  to 
  remark 
  here 
  that 
  neither 
  their 
  upper 
  or 
  

   lower 
  limits 
  have 
  as 
  yet 
  been 
  definitely 
  determined. 
  No 
  addi- 
  

   tional 
  evidence 
  has 
  been 
  gained 
  regarding 
  their 
  age, 
  and 
  they 
  

   are 
  provisionally 
  referred 
  to 
  the 
  Jurassic 
  chiefly 
  on 
  account 
  of 
  

   the 
  great 
  thickness 
  of 
  the 
  sedimentary 
  rocks 
  overlying 
  them, 
  

   which 
  from 
  the 
  remains 
  of 
  Dinosaurs 
  found 
  somewhat 
  

   abundantly 
  in 
  their 
  upper 
  members 
  can 
  scarcely 
  be 
  considered 
  

   of 
  more 
  recent 
  age 
  than 
  Cretaceous. 
  

  

  Cretaceous. 
  

  

  Pueyrredon 
  Series. 
  — 
  Under 
  this 
  name 
  I 
  include 
  some 
  800 
  

   feet 
  of 
  rocks 
  observed 
  in 
  the 
  vicinity 
  of 
  Lake 
  Pueyrredon. 
  The 
  

   strata 
  forming 
  the 
  Pueyrredon 
  Series 
  are 
  immediately 
  but 
  

   unconformably 
  overlaid 
  by 
  the 
  variegated 
  sandstones, 
  Arenis- 
  

   cas 
  Abigarradas 
  beds 
  of 
  Ameghino. 
  The 
  rocks 
  of 
  the 
  Pueyr- 
  

   redon 
  series 
  are 
  well 
  exposed 
  and 
  may 
  be 
  conveniently 
  studied 
  

   on 
  the 
  left 
  bank 
  of 
  Rio 
  Tarde, 
  some 
  four 
  miles 
  above 
  where 
  

   that 
  stream 
  empties 
  into 
  the 
  east 
  end 
  of 
  Lake 
  Pueyrredon. 
  

   At 
  about 
  that 
  distance 
  from 
  its 
  mouth 
  this 
  small 
  stream 
  

   runs 
  through 
  a 
  deep 
  canon, 
  that 
  has 
  been 
  cut 
  in 
  the 
  eastern 
  

   foothills 
  of 
  the 
  Andes, 
  and 
  enters 
  the 
  broad 
  level 
  valley 
  that 
  

   extends 
  eastward 
  from 
  the 
  eastern 
  extremity 
  of 
  the 
  lake. 
  Fol- 
  

   lowing 
  the 
  bed 
  of 
  the 
  stream 
  up 
  the 
  canon 
  to 
  its 
  source, 
  there 
  

   may 
  be 
  seen 
  the 
  most 
  extensive 
  and 
  best 
  exposed 
  geologic 
  

   section 
  observed 
  anywhere 
  in 
  Patagonia 
  during 
  my 
  explora- 
  

   tions 
  in 
  that 
  country. 
  Some 
  5,000 
  feet 
  of 
  sedimentary 
  rocks 
  

   are 
  exposed 
  in 
  a 
  continuous 
  section 
  extending 
  from 
  the 
  Lower 
  

   Cretaceous 
  to 
  late 
  Pliocene 
  deposits. 
  Many 
  distinct 
  geologic 
  

   horizons 
  are 
  represented 
  and 
  most 
  of 
  them 
  are 
  fortunately 
  

   rich 
  in 
  fossil 
  remains 
  in 
  an 
  excellent 
  state 
  of 
  preservation. 
  

  

  Gio 
  beds. 
  — 
  Starting 
  at 
  the 
  base 
  of 
  the 
  section 
  and 
  at 
  the 
  

   mouth 
  of 
  the 
  canon, 
  a 
  deposit 
  of 
  soft 
  green 
  sands 
  or 
  marls 
  

   about 
  100 
  feet 
  thick 
  are 
  seen. 
  Included 
  in 
  the 
  green 
  sands 
  

   are 
  several 
  harder, 
  brown 
  layers, 
  each 
  about 
  two'feet 
  thick 
  and 
  

   composed 
  largely 
  of 
  shells 
  of 
  Exogyra. 
  The 
  proximity 
  of 
  this 
  

   outcrop 
  of 
  these 
  beds 
  to 
  Lake 
  Gio 
  and 
  the 
  Gio 
  basin 
  has 
  sug- 
  

   gested 
  the 
  name 
  Gio 
  beds 
  for 
  these 
  green 
  and 
  brown 
  sand- 
  

   stones. 
  These 
  beds 
  dip 
  gently 
  to 
  the 
  southwest 
  and 
  their 
  

   inclination, 
  together 
  with 
  the 
  rapid 
  increase 
  in 
  the 
  elevation 
  of 
  

   the 
  bed 
  of 
  the 
  stream 
  as 
  one 
  proceeds 
  up 
  the 
  canon, 
  soon 
  

   brings 
  the 
  100 
  feet"" 
  of 
  strata 
  composing 
  them 
  beneath 
  the 
  

  

  * 
  The 
  thickness 
  of 
  the 
  various 
  deposits 
  given 
  in 
  this 
  section 
  are 
  based 
  on 
  

   barometric 
  observations 
  of 
  altitudes: 
  due 
  allowance 
  in 
  each 
  case 
  was 
  made 
  for 
  the 
  

   dip 
  of 
  the 
  different 
  beds. 
  While 
  not 
  absolutely 
  correct, 
  it 
  is 
  believed 
  they 
  are 
  

   fairly 
  accurate. 
  

  

  