﻿GEOLOGIC 
  FORMATIONS 
  OF 
  NEW 
  TORK 
  157 
  

  

  lower 
  strata 
  are 
  traceable 
  in 
  the 
  Appalachians 
  as 
  far 
  as 
  Tennes- 
  

   see, 
  though 
  their 
  upper 
  limestones 
  do 
  not 
  extend 
  beyond 
  the 
  

   Susquehanna. 
  In 
  following 
  them 
  westward 
  from 
  Albany 
  county, 
  

   we 
  find 
  the 
  lower 
  limestones 
  and 
  sandstones 
  thin 
  out 
  rapidly, 
  

   not 
  extending 
  beyond 
  the 
  Niagara 
  in 
  any 
  considerable 
  thickness, 
  

   while 
  the 
  upper 
  limestones 
  are 
  found 
  spreading 
  into 
  the 
  far 
  west. 
  

   This 
  series 
  of 
  rocks 
  which 
  may 
  be 
  considered 
  collectively 
  in 
  its 
  

   effect 
  on 
  topography, 
  belongs 
  partly 
  to 
  the 
  Upper 
  Silurian 
  sys- 
  

   tem 
  and 
  partly 
  to 
  the 
  Devonian 
  and 
  may 
  be 
  divided 
  into 
  two 
  

   parts; 
  the 
  Lower 
  Helderberg 
  limestones 
  which 
  are 
  of 
  Upper 
  Silu- 
  

   rian 
  age, 
  and 
  the 
  Oriskany 
  sandstone 
  and 
  Upper 
  Helderberg 
  lime- 
  

   stones 
  w^hich 
  are 
  included 
  in 
  the 
  Devonian. 
  

  

  Lower 
  Helderberg 
  Group 
  

  

  The 
  subdivisions 
  of 
  this 
  group 
  are 
  as 
  follows: 
  

  

  Thickness 
  

  

  Scutella 
  limestone 
  ) 
  -i^ 
  x^ 
  • 
  aiu 
  ^ 
  

  

  ^_. 
  _ 
  } 
  ^^ 
  it. 
  m 
  Albanv 
  county 
  

  

  upper 
  rentamerus 
  ) 
  

  

  Delthyris, 
  or 
  Catskill 
  shaly 
  

  

  limestone 
  100 
  ft. 
  

  

  Lower 
  Pentamerus 
  limestone 
  65 
  ft. 
  in 
  Albany 
  county 
  

   Tentaculite 
  limestone 
  30 
  ft. 
  " 
  

  

  The 
  Scutella 
  limestone, 
  named 
  from 
  a 
  fossil 
  crinoid 
  which 
  it 
  

   contains, 
  is 
  the 
  uppermost 
  member 
  of 
  the 
  group 
  where 
  it 
  occurs, 
  

   but 
  it 
  has 
  not 
  been 
  found 
  associated 
  with 
  the 
  Upper 
  Pentamerus. 
  

  

  The 
  Lower 
  Pentamerus 
  limestone 
  is 
  coarse-grained, 
  thick- 
  

   bedded 
  and 
  often 
  a 
  concretionary 
  limestone; 
  while 
  the 
  Catskill 
  

   limestone 
  is 
  in 
  thin 
  layers, 
  with 
  much 
  shaly 
  or 
  slaty 
  matter 
  in- 
  

   terstratified 
  with 
  it. 
  

  

  The 
  Lower 
  Helderberg 
  group 
  has 
  its 
  greatest 
  development 
  in 
  

   Albany 
  and 
  Schoharie 
  counties; 
  the 
  subdivisions 
  above 
  given 
  

   may 
  be 
  differentiated 
  in 
  Greene, 
  Albany 
  and 
  Schoharie 
  counties, 
  

   but 
  west 
  of 
  the 
  last 
  county 
  they 
  are 
  not 
  distinct 
  and 
  the 
  group 
  

   itself 
  is 
  indistinguishable 
  from 
  the 
  Salina 
  formation, 
  at 
  the 
  sur- 
  

   face, 
  west 
  of 
  Seneca 
  lake. 
  In 
  the 
  LiA'onia 
  salt 
  shaft, 
  however, 
  

   about 
  35 
  feet 
  of 
  limestone 
  was 
  found 
  containing 
  Tentaculite 
  fos- 
  

  

  