﻿3^ 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  deposition. 
  The 
  confirmation 
  of 
  this 
  conclusion 
  as 
  to 
  the 
  value 
  

   of 
  the 
  Shawangunk 
  grit 
  was 
  afforded 
  by 
  the 
  discovery 
  of 
  an 
  

   extensive 
  eur3Apterid 
  fauna 
  in 
  the 
  interbedded 
  shales 
  of 
  the 
  Shawan- 
  

   gunk 
  grit, 
  as 
  described 
  by 
  the 
  writer 
  [see 
  op. 
  cit. 
  p. 
  294]. 
  Mr 
  

   ITartnagel 
  has 
  indicated 
  the 
  improbability 
  of 
  this 
  Siluric 
  age 
  of. 
  

   the 
  Rensselaer 
  grit 
  or 
  its 
  equivalence 
  to 
  the 
  Oneida-Medina 
  sedi- 
  

   ments 
  with 
  the 
  following 
  arguments 
  : 
  ( 
  i 
  ) 
  the 
  extensive 
  gap 
  by 
  

   nondeposition 
  between 
  the 
  eastern 
  terminus 
  of 
  the 
  Oneida 
  con- 
  

   glomerate, 
  in 
  Herkimer 
  county, 
  and 
  the 
  Rensselaer 
  grit 
  plateau,. 
  

   (2) 
  the 
  long 
  time 
  interval 
  which 
  must 
  be 
  postulated 
  to 
  account 
  

   for 
  the 
  Taconic 
  folding 
  and 
  the 
  erosion 
  that 
  preceded 
  the 
  deposi- 
  

   tion 
  of 
  the 
  grit, 
  (3) 
  the 
  gradual 
  transgression 
  northward 
  of 
  

   arenaceous 
  sediments 
  over 
  the 
  eroded 
  folds, 
  the 
  Shawangunk 
  grits 
  

   being 
  a 
  more 
  southerly 
  and 
  hence 
  earlier 
  representative 
  of 
  such 
  

   transgression. 
  

  

  The 
  region 
  of 
  the 
  Rensselaer 
  grit 
  has 
  recently 
  been 
  carefully 
  

   searched 
  for 
  fossils 
  but 
  though 
  this 
  evidence 
  still 
  fails 
  and 
  its 
  

   absence 
  can 
  not 
  be 
  explained 
  by 
  secondary 
  changes 
  in 
  the 
  rocks,. 
  

   the 
  stratigraphic 
  considerations 
  indicate 
  the 
  propriety 
  of 
  assigning 
  

   a 
  distinctly 
  later 
  than 
  Medina 
  age 
  to 
  this 
  formation. 
  

  

  Near 
  the 
  edge 
  of 
  this 
  plateau 
  no 
  beds 
  of 
  later 
  than 
  Trenton 
  age 
  

   have 
  been 
  observed 
  and 
  there 
  are 
  apparently 
  no 
  outliers 
  to 
  bridge 
  

   the 
  gap 
  between 
  the 
  late 
  Siluric 
  and 
  early 
  Devonic 
  outliers 
  of 
  

   Becraft 
  mountain, 
  Mt 
  Bob 
  and 
  the 
  southernmost 
  outliers 
  of 
  Rens- 
  

   selaer 
  grit 
  in 
  the 
  town 
  of 
  Austerlitz, 
  Columbia 
  co. 
  This 
  last 
  

   named 
  outlier 
  is 
  of 
  especial 
  interest 
  as 
  it 
  lies 
  but 
  20 
  miles 
  north- 
  

   east 
  of 
  Becraft 
  mountain 
  and 
  is 
  a 
  considerable 
  distance 
  south 
  of 
  

   the 
  main 
  Rensselaer 
  grit 
  plateau. 
  For 
  these 
  reasons 
  it 
  has 
  been 
  

   closely 
  studied 
  but 
  found 
  to 
  be 
  in 
  no 
  way 
  lithologically 
  different 
  

   from 
  the 
  grit 
  of 
  Rensselaer 
  county 
  at 
  the 
  north, 
  containing 
  the 
  

   same 
  alternations 
  of 
  grit 
  with 
  red 
  and 
  greenish 
  slates. 
  

  

  From 
  the 
  presence 
  of 
  only 
  the 
  closing 
  stage 
  of 
  the, 
  Upper 
  Siluric 
  

   at 
  Becraft 
  mountain 
  and 
  in 
  the 
  Helderberg 
  near 
  Albany 
  (Country- 
  

   man 
  hill), 
  — 
  the 
  two 
  places 
  where 
  the 
  deposits 
  of 
  the 
  Siluro- 
  

   Devonic 
  basin 
  of 
  New 
  York 
  approach 
  nearest 
  to 
  the 
  Rensselaer 
  

   grit 
  plateau^ 
  it 
  may 
  be 
  properly 
  inferred 
  that 
  the 
  Upper 
  Siluric 
  

   sea 
  of 
  New 
  York 
  did 
  not 
  extend 
  into 
  the 
  present 
  area 
  of 
  the 
  

   Rensselaer 
  grit 
  plateau 
  at 
  any 
  time 
  except 
  possibly 
  in 
  the 
  latest 
  

   (Manlius) 
  stage 
  of 
  that 
  period. 
  In 
  regard 
  to 
  the 
  latter, 
  the 
  prob- 
  

   lem 
  is 
  the 
  same 
  as 
  in 
  regard 
  to 
  the 
  Helderberg 
  limestones 
  in 
  

   general 
  which 
  are 
  exposed 
  at 
  Becraft 
  mountain 
  and 
  of 
  which 
  the 
  

   Rensselaer 
  grit 
  might 
  be 
  conceived 
  as 
  representing 
  the 
  littoral 
  

  

  