﻿Hatcher 
  — 
  Sedimentary 
  Bocks 
  of 
  Southern 
  Patagonia. 
  95 
  

  

  where 
  they 
  should 
  be 
  placed 
  in 
  that 
  series 
  cannot 
  be 
  deter- 
  

   mined 
  until 
  we 
  know 
  more 
  of 
  the 
  Dinosaurs 
  contained 
  in 
  them. 
  

   At 
  present 
  it 
  seems 
  not 
  improbable 
  that 
  they 
  will 
  prove 
  to 
  be 
  

   the 
  equivalent 
  of 
  the 
  Laramie 
  of 
  North 
  America, 
  as 
  they 
  have 
  

   long 
  been 
  considered 
  by 
  Dr. 
  Ameghino 
  and 
  others. 
  

  

  A\ 
  T 
  ith 
  the 
  Guaranitic 
  heels 
  we 
  have 
  reached 
  the 
  uppermost 
  

   of 
  the 
  Mesozoic 
  strata 
  known 
  not 
  only 
  to 
  Patagonia 
  but 
  to 
  

   South 
  America, 
  and 
  assuming 
  that 
  they 
  represent 
  the 
  Laramie 
  

   we 
  find 
  the 
  close 
  of 
  the 
  Mesozoic 
  Era 
  in 
  the 
  southern 
  hemi- 
  

   sphere 
  as 
  in 
  the 
  northern 
  marked 
  by 
  an 
  abundance 
  of 
  gigantic 
  

   and 
  highly 
  specialized 
  Dinosaurs 
  associated 
  with 
  the 
  remains 
  

   of 
  an 
  exceedingly 
  scanty 
  mammalian 
  fauna, 
  its 
  representatives 
  

   of 
  small 
  size, 
  of 
  generalized 
  types 
  and 
  exhibiting 
  even 
  a 
  less 
  

   degree 
  of 
  differentiation 
  and 
  specialization 
  than 
  has 
  been 
  

   observed 
  in 
  the 
  north. 
  

  

  Taken 
  together 
  the 
  Variegated 
  Sandstones, 
  Lower 
  Lignites 
  

   and 
  Guaranitic 
  beds 
  constitute 
  the 
  San 
  Martin 
  Series, 
  of 
  

   Tapper 
  Cretaceous 
  age. 
  The 
  last 
  two 
  should 
  perhaps 
  be 
  entirely 
  

   separated 
  from 
  the 
  Variegated 
  Sandstones 
  and 
  considered 
  as 
  a 
  

   distinct 
  series, 
  since 
  they 
  are 
  unconformable 
  with 
  them 
  and 
  

   were 
  veiy 
  likely 
  of 
  largely 
  fresh- 
  water 
  and 
  aeolian 
  origin, 
  while 
  

   the 
  sandstones, 
  on 
  account 
  of 
  their 
  vast 
  extent 
  and 
  homogeneous 
  

   nature, 
  would 
  seem 
  to 
  have 
  been 
  deposited 
  in 
  a 
  great 
  open 
  body 
  

   of 
  water, 
  probably 
  marine, 
  over 
  which 
  precisely 
  the 
  same 
  

   relative 
  conditions 
  prevailed 
  for 
  an 
  infinitely 
  long 
  period 
  of 
  

   time. 
  

  

  Tertiary. 
  

  

  For 
  a 
  long 
  period 
  following 
  the 
  deposition 
  of 
  the 
  Guarantic 
  

   beds 
  all 
  this 
  region 
  was 
  elevated 
  and 
  subjected 
  to 
  erosion. 
  

   During 
  this 
  long 
  period 
  of 
  early 
  Tertiary 
  erosion 
  the 
  entire 
  

   series 
  of 
  strata 
  constituting 
  the 
  Guaranitic 
  and 
  Lower 
  Lignite 
  

   beds 
  were 
  in 
  many 
  places 
  completely 
  carried 
  away, 
  as 
  has 
  evi- 
  

   dently 
  been 
  the 
  case 
  in 
  the 
  Lake 
  Pueyrredon 
  region 
  ; 
  while 
  

   in 
  the 
  vicinity 
  of 
  Lake 
  San 
  Martin 
  and 
  at 
  various 
  localities 
  

   over 
  the 
  interior, 
  remnants 
  of 
  the 
  Guaranitic 
  beds 
  are 
  still 
  left 
  

   having 
  partially 
  resisted 
  the 
  early 
  Tertiary 
  erosion 
  to 
  which 
  

   they 
  were 
  subjected. 
  The 
  valleys 
  which 
  were 
  then 
  cut 
  deep 
  

   in 
  the 
  surface, 
  frequently 
  passing 
  quite 
  through 
  the 
  Guaranitic 
  

   and 
  Lower 
  Lignite 
  beds 
  and 
  into 
  the 
  rocks 
  of 
  the 
  Variegated 
  

   Sandstones, 
  may 
  now 
  be 
  seen 
  in 
  many 
  localities 
  tilled 
  with 
  a 
  

   series 
  of 
  Tertiary 
  deposits 
  varying 
  in 
  age 
  from 
  early 
  Eocene 
  to 
  

   Pliocene. 
  Such 
  deposits 
  have 
  been 
  sometimes 
  of 
  marine, 
  

   sometimes 
  of 
  fresh-water 
  or 
  aeolian 
  origin. 
  The 
  complex 
  

   nature 
  of 
  the 
  stratigraphy 
  of 
  the 
  region 
  in 
  which 
  they 
  now 
  

   occur, 
  due 
  to 
  the 
  eroded 
  nature 
  of 
  the 
  surface 
  upon 
  which 
  

   they 
  were 
  laid 
  down, 
  has 
  led 
  Dr. 
  Ameghino 
  to 
  consider 
  such 
  

  

  