﻿138 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  System 
  

  

  Salina 
  

  

  Upper 
  Silurian 
  < 
  Niagara 
  

  

  ^Medina 
  

  

  Lower 
  Silurian 
  < 
  

  

  Group 
  Stage 
  

  

  r 
  Upper 
  Pentamerus 
  limestone 
  

   Lower 
  Helderberg< 
  Delthyris 
  shaly 
  limestone 
  

  

  [Lower 
  Pentamerus 
  limestone 
  

  

  Shale, 
  limestone, 
  salt 
  and 
  

   gypsum 
  

   r 
  Niagara 
  shale 
  and 
  limestone 
  

   i 
  Clinton 
  sandstone, 
  limestone 
  

   [ 
  and 
  shale 
  

   ( 
  Medina 
  sandstone 
  

   i 
  Oneida 
  conglomerate 
  

   r 
  Pulaski 
  and 
  Lorraine 
  shales 
  

   < 
  Frankfort 
  slate 
  

   I^Utica 
  slate 
  

   r 
  Trenton 
  1 
  

  

  J 
  Black 
  river 
  [■.. 
  . 
  

  

  Birdseye 
  [I'meBtoneg 
  

  

  (^ 
  Chazy 
  J 
  

  

  r 
  Hudson 
  river 
  

  

  Trenton 
  

  

  Cambrian 
  

   Archaean 
  

  

  , 
  Calcif 
  erouB 
  

  

  r 
  Potsdam 
  

   < 
  Acadian 
  

   (^ 
  Georgian 
  

  

  Sandstone 
  and 
  limestone 
  

  

  Quartzite 
  and 
  slate 
  

   gneisses 
  and 
  Granites 
  

  

  Archaean 
  

  

  This 
  name 
  was 
  proposed 
  by 
  Prof. 
  J. 
  D. 
  Dana 
  to 
  include 
  those 
  

   ancient 
  crystalline 
  rocks, 
  which 
  in 
  nearly 
  all 
  countries 
  are 
  seen 
  

   to 
  underlie 
  the 
  oldest 
  f 
  ossiliferous 
  strata. 
  

  

  Although 
  various 
  subdivisions 
  and 
  classifications 
  have 
  been 
  

   proposed 
  at 
  times, 
  in 
  the 
  light 
  of 
  present 
  knowledge 
  their 
  accu- 
  

   racy 
  is 
  uncertain 
  and 
  they 
  will 
  not 
  be 
  mentioned 
  here. 
  

  

  The 
  Laurentian 
  rocks 
  of 
  Canada 
  may 
  be 
  regarded 
  as 
  types 
  of 
  

   the 
  Archaean. 
  

  

  In 
  New 
  York, 
  as 
  elsewhere, 
  this 
  system 
  is 
  represented 
  by 
  a 
  

   series 
  of 
  crystalline 
  rocks 
  including 
  gneiss, 
  granite, 
  diorite 
  and 
  

   norite. 
  Crystalline 
  limestone 
  is 
  often 
  associated 
  with 
  them, 
  but 
  

   we 
  do 
  not 
  know 
  whether 
  it 
  should 
  be 
  regarded 
  as 
  truly 
  Archaean. 
  

   These 
  rocks 
  are 
  exposed 
  where 
  uplifts 
  from 
  below 
  in 
  early 
  time 
  

   raised 
  them 
  up 
  to 
  form 
  islands 
  in 
  the 
  Palaeozoic 
  seas, 
  or 
  in 
  later 
  

   time 
  have 
  caused 
  them 
  to 
  break 
  through 
  the 
  overlying 
  strata. 
  

   An 
  instance 
  of 
  the 
  latter 
  occurs 
  at 
  Littlefalls, 
  where 
  the 
  hard, 
  

   red 
  and 
  gray 
  granite 
  has 
  been 
  forced 
  up 
  in 
  ja 
  dome 
  and 
  appears 
  

  

  