﻿34 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  either 
  completely 
  pushed 
  aside 
  the 
  Grenville 
  or 
  melted 
  it 
  into 
  itself, 
  

   the 
  former 
  being 
  the 
  more 
  likely. 
  Many 
  of 
  the 
  highest 
  points 
  within 
  

   the 
  Adirondacks, 
  like 
  Mt 
  Marcy, 
  are 
  in 
  this 
  anorthosite 
  area. 
  

  

  The 
  next 
  clearly 
  recorded 
  event, 
  after 
  the 
  anorthosite 
  intrusion, 
  

   was 
  very 
  widespread 
  igneous 
  activity 
  when 
  ithe 
  rocks 
  of 
  the 
  granite- 
  

   syenite 
  series,, 
  now 
  so 
  well 
  known 
  in 
  the 
  Adirondacks, 
  were 
  forced 
  

   upward 
  into 
  the 
  Grenville 
  sediments. 
  To 
  be 
  precise, 
  there 
  were 
  at 
  

   least 
  two 
  or 
  three 
  periods 
  of 
  intrusions 
  of 
  such 
  rocks, 
  the 
  oldest 
  

   probably 
  being 
  represented 
  by 
  the 
  so-called 
  Laurentian 
  granite 
  of 
  

   the 
  Thousand 
  Islands 
  region. 
  For 
  our 
  purpose 
  it 
  will 
  suffice 
  to 
  re- 
  

   gard 
  these 
  as 
  having 
  all 
  been 
  intruded 
  at 
  about 
  the 
  same 
  time, 
  since 
  

   the 
  sum 
  total 
  of 
  effects 
  is 
  much 
  the 
  same 
  as 
  though 
  there 
  had 
  been 
  

   but 
  a 
  single 
  period 
  of 
  activity. 
  Granite 
  is 
  a 
  plutonic, 
  igneous 
  rock 
  

   which 
  consists 
  essentially 
  of 
  quartz 
  and 
  feldspar 
  (orthoclase), 
  

  

  K 
  A 
  XI 
  Grsnu/Jle 
  \x 
  x 
  % 
  x\Anorth6sHe 
  Y^wfyenite- 
  granite 
  I+++ 
  +| 
  Gabbro 
  or 
  

  

  HAM 
  series 
  |x 
  y 
  x 
  *[ 
  K 
  V 
  f 
  \ 
  series 
  kV+l 
  ^k^ 
  dike 
  

  

  Fig. 
  12 
  Generalized 
  section 
  showing 
  the 
  relations 
  of 
  the 
  most 
  common 
  

   Precambric 
  (Adirondack) 
  rocks 
  to 
  each 
  other 
  and 
  how 
  their 
  relative 
  ages 
  

   are 
  determined. 
  

  

  together 
  with 
  more 
  or 
  less 
  black 
  mica,, 
  hornblende, 
  or 
  augite. 
  Syenite 
  

   is 
  the 
  same 
  except 
  that 
  quartz 
  is 
  much 
  less 
  prominent 
  or 
  lacking. 
  

   The 
  fresh 
  rock 
  is 
  of 
  a 
  greenish 
  gray 
  or 
  pinkish 
  gray 
  color, 
  while 
  

   on 
  weathered 
  surfaces 
  the 
  color 
  is 
  usually 
  light 
  brown. 
  Many 
  of 
  

   the 
  highest 
  mountains 
  outside 
  the 
  anorthosite 
  area 
  are 
  of 
  granite 
  or 
  

   syenite. 
  

  

  The 
  present 
  distribution 
  of 
  these 
  rocks 
  shows 
  that 
  the 
  molten 
  

   masses 
  broke 
  into 
  the 
  Grenville 
  in 
  very 
  irregular 
  fashion, 
  sometimes 
  

   pushing 
  the 
  Grenville 
  aside; 
  sometimes 
  enveloping 
  great 
  or 
  small 
  

   masses 
  within 
  the 
  molten 
  flood 
  ; 
  or, 
  in 
  other 
  cases, 
  apparently 
  leav- 
  

   ing 
  large 
  Grenville 
  masses 
  intact. 
  All 
  portions 
  of 
  the 
  Adirondacks 
  

   felt 
  the 
  force 
  of 
  the 
  intrusions 
  and 
  a 
  detailed 
  geologic 
  map 
  of 
  the 
  

   region 
  would 
  show 
  a 
  decided 
  patchwork 
  effect 
  (see 
  figure 
  13) 
  due 
  

   to 
  the 
  irregular 
  manner 
  in 
  which 
  the 
  Grenville 
  has 
  been 
  cut 
  up 
  by 
  

   the 
  igneous 
  rocks. 
  These 
  igneous 
  rocks 
  are 
  generally 
  easily 
  distin- 
  

   guished 
  from 
  the 
  old 
  sediments 
  because 
  of 
  their 
  homogeneity 
  in 
  

  

  