﻿S3 
  Hatcher 
  — 
  Sedimentary 
  Rocks 
  of 
  Southern 
  Patagonia. 
  

  

  The 
  map 
  prepared 
  and 
  published 
  by 
  Dr. 
  Francisco 
  P. 
  

   Moreno 
  in 
  the 
  Geographical 
  Journal 
  of 
  the 
  Royal 
  Geograph- 
  

   ical 
  Society 
  of 
  London, 
  accompanying 
  a 
  paper 
  by 
  the 
  same 
  

   author 
  entitled 
  "Explorations 
  in 
  Patagonia" 
  and 
  published 
  in 
  

   the 
  September 
  and 
  October 
  numbers 
  of 
  the 
  same 
  Journal 
  for 
  

   1899, 
  has 
  served 
  as 
  the 
  basis 
  for 
  the 
  present 
  map. 
  It 
  has 
  been 
  

   redrawn 
  by 
  Mr. 
  Howard 
  Logan, 
  with 
  the 
  introduction 
  of 
  a 
  few 
  

   additions 
  and 
  corrections 
  made 
  by 
  myself. 
  The 
  map 
  is 
  essen- 
  

   tially 
  the 
  work 
  of 
  the 
  Argentine 
  Limit 
  Commission 
  under 
  the 
  

   direction 
  of 
  Dr. 
  Moreno. 
  While 
  not 
  complete 
  it 
  is 
  fairly 
  accu- 
  

   rate 
  and 
  is 
  by 
  far 
  the 
  best 
  of 
  any 
  of 
  the 
  maps 
  yet 
  published 
  of 
  

   this 
  region. 
  

  

  Physiographic 
  Features 
  of 
  Patagonia. 
  

  

  Before 
  entering 
  upon 
  a 
  discussion 
  of 
  the 
  geology 
  of 
  Patago- 
  

   nia 
  it 
  may 
  be 
  well 
  to 
  refer 
  briefly 
  to 
  the 
  principal 
  physio- 
  

   graphic 
  features 
  of 
  the 
  country.* 
  Patagonia 
  and 
  Tierra 
  del 
  

   Puego 
  are 
  naturally 
  divided 
  into 
  two 
  sharply 
  defined 
  and 
  easily 
  

   characterized 
  regions, 
  a 
  western, 
  extremely 
  mountainous, 
  region 
  

   and 
  an 
  eastern, 
  comparatively 
  level, 
  plain. 
  The 
  mountains 
  of 
  

   the 
  western 
  region 
  are 
  formed 
  by 
  three 
  parallel 
  ranges 
  sepa- 
  

   rated 
  by 
  two 
  deep, 
  narrow, 
  longitudinal 
  valleys. 
  Throughout 
  

   the 
  eastern 
  plains 
  region 
  several 
  features 
  combine 
  to 
  break 
  the 
  

   monotony 
  and 
  lend 
  variety 
  to 
  what 
  would 
  otherwise 
  be 
  an 
  ex- 
  

   ceedingly 
  dreary 
  landscape. 
  Chief 
  among 
  such 
  features 
  are 
  

   the 
  great 
  transverse 
  valleys 
  that 
  cross 
  the 
  Patagonian 
  plains 
  

   from 
  east 
  to 
  west 
  and 
  form 
  the 
  principal 
  drainage 
  systems 
  of 
  

   those 
  plains. 
  These 
  valleys 
  frequently 
  attain 
  a 
  depth 
  near 
  the 
  

   Andes 
  of 
  more 
  than 
  2000 
  feet 
  below 
  the 
  surface 
  of 
  the 
  neigh- 
  

   boring 
  plains. 
  They 
  are 
  all 
  true 
  valleys 
  of 
  erosion, 
  while 
  the 
  

   longitudinal 
  valleys 
  of 
  the 
  western 
  mountainous 
  region 
  are 
  of 
  

   tectonic 
  origin. 
  It 
  is 
  along 
  the 
  bluffs 
  of 
  the 
  sea 
  and 
  in 
  the 
  

   exposures 
  over 
  the 
  slopes 
  of 
  these 
  valleys 
  and 
  their 
  less 
  impor- 
  

   tant 
  tributaries 
  that 
  the 
  best 
  opportunities 
  are 
  offered 
  for 
  

   studying 
  the 
  geology 
  of 
  Patagonia. 
  

  

  Mesozoic. 
  

  

  Jurassic? 
  — 
  The 
  oldest 
  sedimentary 
  rocks 
  observed 
  by 
  the 
  

   writer 
  anywhere 
  in 
  Patagonia 
  consist 
  of 
  a 
  series 
  of 
  black, 
  very 
  

   hard 
  but 
  much 
  fractured 
  slates 
  with 
  remains 
  of 
  Ammonites 
  

   fairly 
  abundant 
  but 
  not 
  sufficiently 
  well 
  preserved 
  to 
  admit 
  of 
  

   identification. 
  These 
  beds 
  I 
  have 
  already 
  noticed 
  in 
  my 
  

   former 
  paper 
  on 
  the 
  geology 
  of 
  Patagonia, 
  and 
  have 
  named 
  

  

  * 
  For 
  a 
  further 
  description 
  of 
  the 
  geographic 
  features 
  of 
  Patagonia, 
  see 
  paper 
  

   on 
  that 
  subject 
  by 
  J. 
  B. 
  Hatcher 
  in 
  The 
  National 
  Geographic 
  Magazine, 
  Feb. 
  

   1900. 
  

  

  