﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  33 
  

  

  very 
  similar 
  to 
  graphite, 
  occurs 
  in 
  the 
  Carbonic 
  strata 
  of 
  Pennsyl- 
  

   vania, 
  and 
  is 
  derived 
  from 
  plants 
  through 
  the 
  process 
  of 
  carboni- 
  

   zation. 
  Graphitic 
  anthracite 
  of 
  like 
  origin 
  occurs 
  in 
  a 
  smaller 
  way 
  in 
  

   Rhode 
  Island. 
  Hence 
  it 
  seems 
  likely 
  that 
  the 
  graphite 
  of 
  the 
  Gren- 
  

   ville 
  represents 
  the 
  remains 
  of 
  plants, 
  probably 
  of 
  the 
  seaweed 
  type 
  

   since 
  there 
  is 
  much 
  evidence 
  against 
  the 
  view 
  that 
  any 
  of 
  the 
  higher 
  

   land 
  plants 
  existed 
  at 
  that 
  very 
  early 
  time. 
  This 
  by 
  no 
  means 
  proves 
  

   the 
  absence 
  of 
  animals 
  from 
  the 
  Grenville 
  ocean, 
  because 
  animals 
  

   with 
  only 
  soft 
  parts 
  would 
  have 
  left 
  no 
  record, 
  while 
  calcareous 
  or 
  

   silicious 
  shells 
  would 
  doubtless 
  have 
  been 
  recrystallized 
  by 
  the 
  

   severe 
  processes 
  of 
  metamorphism 
  to 
  which 
  these 
  rocks 
  have 
  been 
  

   subjected. 
  

  

  EARLY 
  PRECAMBRIC 
  IGNEOUS 
  ACTIVITY 
  

  

  After 
  the 
  accumulation 
  of 
  the 
  Grenville 
  sediments, 
  igneous 
  activity, 
  

   took 
  place 
  on 
  a 
  large 
  scale, 
  when 
  great 
  masses 
  of 
  molten 
  rock 
  were 
  

   pushed 
  or 
  intruded 
  into 
  the 
  sediments 
  from 
  below. 
  Several 
  differ- 
  

   ent 
  times 
  of 
  igneous 
  activity 
  have 
  been 
  definitely 
  recognized 
  and 
  the 
  

   general 
  effect 
  of 
  the 
  great 
  invasions 
  of 
  molten 
  rocks 
  was 
  to 
  break 
  

   the 
  Grenville 
  up 
  into 
  patches. 
  In 
  many 
  cases 
  considerable 
  masses 
  

   of 
  Grenville 
  were 
  pushed 
  aside 
  or 
  displaced 
  by 
  the 
  molten 
  masses 
  

   while, 
  to 
  a 
  greater 
  or 
  less 
  extent, 
  there 
  may 
  have 
  been 
  an 
  actual 
  

   melting 
  in 
  or 
  assimilation 
  of 
  Grenville 
  rocks 
  by 
  the 
  molten 
  intru- 
  

   sions. 
  As 
  we 
  have 
  already 
  learned, 
  igneous 
  rocks 
  are 
  those 
  which 
  

   have 
  cooled 
  from 
  a 
  molten 
  condition, 
  and 
  of 
  these 
  there 
  are 
  two 
  

   important 
  types, 
  called 
  respectively, 
  plutonic 
  and 
  volcanic. 
  Both 
  

   of 
  these 
  types 
  of 
  igneous 
  rocks 
  are 
  found 
  in 
  the 
  Adirondacks, 
  but 
  

   the 
  plutonics 
  are 
  by 
  far 
  the 
  more 
  prominently 
  developed. 
  

  

  So 
  far 
  as 
  we 
  know, 
  the 
  first 
  great 
  intrusion 
  of 
  molten 
  rock 
  in 
  the 
  

   Adirondacks 
  is 
  represented 
  by 
  the 
  present 
  large 
  area 
  of 
  so-called 
  

   anorthosite 
  in 
  Essex 
  and 
  Franklin 
  counties. 
  This 
  is 
  a 
  very 
  

   coarse-grained, 
  plutonic 
  rock 
  of 
  bluish 
  gray 
  color 
  when 
  fresh 
  and 
  

   consists 
  chiefly 
  of 
  a 
  feldspar 
  (labradorite). 
  The 
  intrusion 
  was 
  

   practically 
  confined 
  to 
  a 
  single 
  area 
  comprising 
  about 
  1200 
  square 
  

   miles. 
  That 
  this 
  rock 
  is 
  younger 
  than 
  the 
  Grenville 
  is 
  demonstrated 
  

   by 
  the 
  fact 
  that 
  tongues 
  of 
  the 
  anorthosite 
  have 
  been 
  observed 
  cut- 
  

   ting 
  through 
  the 
  Grenville 
  (see 
  figure 
  12). 
  This 
  intrusion 
  differs 
  

   from 
  the 
  later 
  intrusions 
  in 
  that 
  it 
  was 
  practically 
  a 
  single 
  great 
  mass 
  

   which 
  broke 
  its 
  way 
  through 
  the 
  Grenville 
  in 
  but 
  one 
  place 
  in 
  the 
  

   whole 
  Adirondack 
  region. 
  In 
  a 
  few 
  cases 
  small 
  patches 
  of 
  Gren- 
  

   ville 
  were 
  caught 
  in 
  the 
  molten 
  flood 
  and 
  may 
  now 
  be 
  seen 
  within 
  

   the 
  anorthosite 
  mass. 
  For 
  the 
  most 
  part, 
  however, 
  the 
  molten 
  rocks 
  

  

  