﻿448 
  J. 
  Barrett 
  — 
  TJjpjper 
  Devonian 
  Delta 
  of 
  the 
  

  

  tion 
  in 
  central 
  New 
  York, 
  or 
  that 
  they 
  are 
  'equivalent 
  to 
  the 
  coarse 
  

   beds 
  of 
  Chemung 
  age 
  in 
  the 
  southern 
  Catskills.' 
  "* 
  

  

  This 
  formation 
  has 
  everywhere 
  an 
  eroded 
  top 
  but 
  still 
  in 
  

   the 
  deepest 
  part 
  of 
  the 
  syncline 
  retains 
  a 
  thickness 
  of 
  2,500 
  

   feet. 
  

  

  The 
  Rensselaer 
  grit.\ 
  

  

  Between 
  the 
  Hudson 
  River 
  and 
  the 
  northwestern 
  side 
  of 
  

   Massachusetts 
  stretches 
  a 
  tableland 
  known 
  as 
  the 
  Rensselaer 
  

   Plateau. 
  It 
  is 
  underlain 
  typically 
  by 
  a 
  dark 
  green 
  grit 
  or 
  

   graywacke, 
  in 
  some 
  beds 
  calcareous, 
  in 
  others 
  conglomeratic. 
  

   The 
  conglomerates 
  are 
  rather 
  fine-grained, 
  the 
  pebbles 
  rarely 
  

   reaching 
  an 
  inch 
  in 
  diameter, 
  and 
  are 
  angular 
  or 
  subangular 
  

   fragments 
  of 
  quartz, 
  feldspar, 
  gneiss, 
  slate, 
  and 
  red 
  quartzite 
  ; 
  

   the 
  relative 
  abundance 
  being 
  in 
  the 
  order 
  named. 
  Some 
  dark 
  

   purple 
  or 
  reddish 
  slates 
  occur 
  and 
  rarely 
  angular 
  fragments 
  of 
  

   limestone 
  in 
  certain 
  conglomerate 
  beds. 
  The 
  formation 
  rests 
  

   unconformably 
  on 
  the 
  Cambrian 
  and 
  Ordovician 
  formations, 
  as 
  

   shown 
  by 
  the 
  character 
  of 
  the 
  conglomerates 
  more 
  clearly 
  than 
  

   the 
  structure, 
  but 
  another 
  orogenic 
  disturbance 
  has 
  followed 
  its 
  

   deposition, 
  producing 
  folding 
  and 
  metamorphism. 
  Dale 
  notes 
  

   that 
  measurements 
  of 
  the 
  total 
  thickness 
  are 
  especially 
  difficult 
  

   to 
  make, 
  but 
  estimates 
  that 
  in 
  one 
  exposure 
  at 
  least 
  2,000 
  feet 
  

   remain. 
  

  

  The 
  formation 
  is 
  younger 
  than 
  the 
  Ordovician 
  and 
  was 
  for- 
  

   merly 
  assumed 
  to 
  be 
  of 
  early 
  Silurian 
  age, 
  but 
  as 
  the 
  result 
  of 
  

   studies 
  by 
  the 
  New 
  York 
  geologists, 
  John 
  M. 
  Clarke 
  expresses 
  

   the 
  opinion 
  that 
  

  

  " 
  The 
  evidence 
  compels 
  us 
  to 
  grant 
  that 
  the 
  Rensselaer 
  grit 
  is 
  

   of 
  later 
  than 
  Siluric 
  age 
  ; 
  there 
  is 
  some 
  good 
  reason 
  for 
  regarding 
  

   it 
  an 
  eastern 
  deposit 
  contemporary 
  with 
  the 
  early 
  Devonic, 
  but 
  

   the 
  alternative 
  proposition 
  stands 
  open, 
  that 
  its 
  estuarine 
  charac- 
  

   ter 
  and 
  great 
  thickness 
  suggest 
  identity 
  with 
  the 
  Catskill 
  beds 
  

   which 
  stand 
  sheer 
  on 
  the 
  other 
  side 
  of 
  the 
  Hudson 
  River 
  in 
  

   heights 
  of 
  several 
  thousand 
  feet 
  and 
  only 
  30 
  miles 
  away 
  from 
  the 
  

   outlier 
  at 
  Austerlitz."J; 
  

  

  From 
  this 
  view 
  the 
  present 
  writer 
  would 
  differ 
  slightly. 
  

   The 
  argillaceous 
  component 
  of 
  the 
  Oneonta 
  and 
  Catskill 
  beds 
  

   is 
  colored 
  red 
  and 
  stands 
  in 
  contrast 
  to 
  the 
  grays, 
  greens, 
  and 
  

   yellows 
  of 
  their 
  marine 
  equivalents. 
  In 
  the 
  Middle 
  Devonian, 
  

   however, 
  the 
  marine 
  muds 
  are 
  dark 
  gray 
  to 
  black, 
  and 
  the 
  

  

  * 
  Kiimrael 
  and 
  Weller. 
  Annual 
  Report 
  of 
  the 
  State 
  Geologist 
  of 
  New- 
  

   Jersey 
  for 
  1901, 
  pp. 
  23, 
  24. 
  

  

  f 
  See 
  T. 
  Nelson 
  Dale, 
  The 
  Rensselaer 
  Grit 
  Plateau 
  in 
  New 
  York. 
  U. 
  S. 
  

   Geol. 
  Surv., 
  13th 
  Ann. 
  Rept., 
  Pt. 
  II., 
  1893, 
  pp. 
  291-340. 
  

  

  \ 
  Early 
  Devonic 
  history 
  of 
  New 
  York 
  and 
  eastern 
  North 
  America. 
  N. 
  Y. 
  

   State 
  Museum, 
  Memoir 
  9, 
  II, 
  pp. 
  160, 
  161, 
  1909. 
  

  

  