﻿Hatcher 
  — 
  Sedimentary 
  Rocks 
  of 
  Southern 
  Patagonia. 
  105 
  

  

  The 
  Santa 
  Cruz 
  beds. 
  — 
  Immediately 
  and 
  conformably 
  over- 
  

   lying 
  the 
  Patagoniau 
  beds 
  are 
  the 
  Santa 
  Crnz 
  beds, 
  composed 
  

   of 
  a 
  series 
  of 
  usually 
  soft 
  and 
  light-colored 
  sandstones 
  and 
  

   shales, 
  rich 
  in 
  the 
  remains 
  of 
  birds 
  and 
  mammals, 
  but 
  for 
  the 
  

   most 
  part 
  remarkably 
  destitute 
  of 
  any 
  mollnscan 
  or 
  other 
  

   invertebrate 
  fossils, 
  in 
  marked 
  contrast 
  with 
  the 
  underlying 
  

   beds. 
  At 
  the 
  base 
  the 
  Santa 
  Cruz 
  beds 
  are 
  sometimes 
  inter- 
  

   stratified 
  with 
  the 
  uppermost 
  Patagonian 
  beds. 
  This 
  condi- 
  

   tion 
  was 
  first 
  recognized 
  and 
  pointed 
  out 
  by 
  the 
  Ameghinos. 
  

   On 
  my 
  first 
  expedition 
  to 
  Patagonia 
  I 
  was 
  unable 
  to 
  find 
  any 
  

   conclusive 
  evidence 
  of 
  such 
  interstratification, 
  and 
  from 
  certain 
  

   apparent 
  unconformities 
  noticed 
  at 
  Shell 
  Gap 
  and 
  Sierra 
  Oveja 
  

   on 
  the 
  Rio 
  Chico, 
  I 
  concluded 
  that 
  the 
  Santa 
  Cruz 
  beds 
  were 
  

   not 
  interstratified 
  with 
  the 
  Patagonian 
  beds 
  but 
  were 
  separated 
  

   from 
  them 
  by 
  a 
  considerable 
  time 
  interval. 
  Subsequent 
  

   explorations 
  have, 
  however, 
  convinced 
  me 
  of 
  my 
  error 
  and 
  I 
  

   have 
  been 
  able 
  to 
  verify 
  the 
  observations 
  of 
  Seiior 
  Carlos 
  

   Ameghino 
  at 
  the 
  Mt. 
  of 
  Observation 
  and 
  to 
  make 
  similar 
  

   observations 
  in 
  the 
  Lake 
  Pueyrredon 
  section 
  and 
  at 
  other 
  

   localities 
  throughout 
  the 
  interior. 
  

  

  The 
  Santa 
  Cruz 
  beds 
  are 
  first 
  seen 
  in 
  the 
  Atlantic 
  coast 
  sec- 
  

   tion 
  near 
  Mt. 
  Observation 
  south 
  of 
  the 
  Santa 
  Cruz 
  River, 
  

   where 
  they 
  form 
  the 
  summits 
  of 
  the 
  higher 
  bluffs 
  bordering 
  

   the 
  coast, 
  From 
  this 
  point 
  southward 
  they 
  form 
  a 
  constantly 
  

   increasing 
  proportion 
  of 
  the 
  total 
  thickness 
  of 
  the 
  bluffs 
  of 
  

   the 
  sea 
  until, 
  on 
  the 
  south 
  side 
  of 
  Coy 
  Inlet, 
  the 
  entire 
  series 
  

   of 
  strata 
  forming 
  the 
  bluffs, 
  with 
  a 
  maximum 
  thickness 
  of 
  600 
  

   feet, 
  are 
  composed 
  of 
  rocks 
  of 
  the 
  Santa 
  Cruz 
  beds, 
  which 
  

   extend 
  uninterruptedly 
  to 
  the 
  mouth 
  of 
  the 
  Gallegos 
  River. 
  

   It 
  will 
  thus 
  be 
  seen 
  that 
  the 
  Santa 
  Cruz 
  beds 
  appear 
  contin- 
  

   uously 
  in 
  the 
  bluffs 
  of 
  the 
  Atlantic 
  coast 
  from 
  Cape 
  Fair- 
  

   weather 
  north 
  for 
  a 
  distance 
  of 
  about 
  100 
  miles. 
  They 
  also 
  

   cover 
  the 
  entire 
  plains 
  region 
  between 
  this 
  coast 
  line 
  and 
  the 
  

   Andes, 
  and 
  toward 
  the 
  west 
  they 
  stretch 
  far 
  to 
  the 
  northward, 
  

   extending 
  even 
  as 
  far 
  as 
  the 
  latitude 
  of 
  Lake 
  Buenos 
  Ayres, 
  

   or 
  16° 
  30' 
  S. 
  

  

  The 
  maximum 
  development 
  so 
  far 
  observed 
  in 
  the 
  Santa 
  

   Cruz 
  beds 
  may 
  be 
  seen 
  in 
  the 
  Lake 
  Pueyrredon 
  and 
  Rio 
  Tarde 
  

   section, 
  where 
  they 
  overlie 
  the 
  Patagonian 
  beds 
  and 
  show 
  a 
  

   thickness 
  of 
  1,500 
  feet. 
  From 
  Lake 
  Pueyrredon 
  the 
  Santa 
  

   Cruz 
  beds 
  may 
  be 
  traced 
  in 
  an 
  almost 
  unbroken 
  series 
  of 
  out- 
  

   crops 
  extending 
  for 
  ,more 
  than 
  300 
  miles 
  along 
  the 
  eastern 
  

   range 
  of 
  the 
  Andes. 
  

  

  From 
  the 
  entirely 
  different 
  character 
  of 
  the 
  fossils 
  encoun- 
  

   tered 
  it 
  is 
  evident 
  that 
  there 
  was 
  a 
  considerable 
  change 
  in 
  the 
  

   physical 
  features 
  of 
  this 
  region 
  during 
  the 
  period 
  which 
  

   marked 
  the 
  close 
  of 
  the 
  deposition 
  of 
  the 
  Patagonian 
  beds 
  and 
  

  

  