﻿160 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  the 
  Potsdam 
  sandstone, 
  and 
  were 
  called 
  Taconic. 
  This 
  range 
  of 
  

   rocks 
  contains 
  very 
  few 
  fossils 
  or 
  none 
  in 
  most 
  localities, 
  and 
  

   geologists 
  have 
  been 
  obliged 
  to 
  study 
  it 
  without 
  the 
  aid 
  which 
  

   fossils 
  would 
  have 
  given 
  in 
  explaining 
  the 
  relation 
  and 
  true 
  posi- 
  

   tion 
  of 
  its 
  confused 
  and 
  contorted 
  strata. 
  The 
  general 
  conclu- 
  

   sion 
  has 
  been 
  that 
  this 
  series 
  of 
  strata 
  is 
  not 
  a 
  separate 
  and 
  

   distinct 
  one, 
  but 
  merely 
  the 
  eastward 
  extension 
  of 
  the 
  rocks 
  older 
  

   than 
  the 
  Medina 
  and 
  Clinton 
  groups, 
  changed 
  in 
  character 
  or 
  

   * 
  metamorphosed 
  ' 
  by 
  the 
  effect 
  of 
  heat 
  and 
  pressure. 
  The 
  work 
  

   of 
  Walcott 
  and 
  others 
  has 
  proved 
  that 
  most 
  of 
  the 
  schistose 
  rocks 
  

   are 
  of 
  Hudson 
  river 
  age, 
  though 
  a 
  portion 
  of 
  them 
  contain 
  Lower 
  

   and 
  Middle 
  Cambrian 
  fossils 
  and 
  are 
  therefore 
  distinct. 
  

  

  In 
  Westchester 
  and 
  New 
  York 
  counties, 
  rocks 
  of 
  Hudson 
  river 
  

   age 
  cover 
  large 
  areas. 
  They 
  are, 
  however, 
  metamorphosed 
  into 
  

   mica 
  schist 
  and 
  contain 
  no 
  fossils. 
  

  

  Life 
  of 
  the 
  Lower 
  Silurian 
  

  

  The 
  animal 
  life 
  of 
  this 
  system 
  w^as 
  also 
  marine 
  and 
  chiefly 
  

   represented 
  by 
  sponges, 
  corals, 
  brachiopods, 
  mollusks 
  and 
  crus- 
  

   taceans. 
  Cephalopods 
  were 
  the 
  dominant 
  forms 
  and 
  were 
  of 
  

   great 
  size. 
  Fishes 
  have 
  recently 
  been 
  announced 
  by 
  C. 
  D. 
  Wal- 
  

   cott. 
  No 
  land 
  animals 
  are 
  known 
  to 
  have 
  existed 
  except 
  some 
  

   insects 
  reported 
  from 
  Europe. 
  Vegetable 
  life 
  was 
  represented 
  

   by 
  sea 
  weeds, 
  though 
  a 
  land 
  plant 
  has 
  been 
  found 
  in 
  Great 
  

   Britain. 
  

  

  UPPER 
  SILURIAN 
  SYSTEM 
  

  

  The 
  Upper 
  Silurian 
  system, 
  which 
  is 
  the 
  upper 
  division 
  of 
  the 
  

   original 
  Silurian 
  system, 
  consists 
  in 
  New 
  York 
  state 
  of 
  the 
  fol- 
  

   lowing 
  divisions: 
  

  

  System 
  Group 
  

  

  /^ 
  Lower 
  Helderberg 
  

  

  Waterlime 
  

  

  Upper 
  Silurian 
  -{ 
  Niagara 
  

  

  Clinton 
  

   Medina 
  

   Oneida 
  

  

  Onondaga 
  Salt 
  Group 
  1 
  q 
  r 
  " 
  

  

  