﻿NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  GENERAL 
  GEOLOGIC 
  FEATURES 
  

  

  Under 
  this 
  heading 
  it 
  is 
  proposed 
  to 
  briefly 
  outline 
  the 
  

   geologic 
  history 
  of 
  the 
  whole 
  Adirondack 
  region 
  so 
  that 
  the 
  

   detailed 
  study 
  presented 
  in 
  this 
  report 
  may 
  be 
  made 
  more 
  in- 
  

   telligible 
  to 
  the 
  reader. 
  This 
  outline 
  is 
  based 
  largely 
  upon 
  the 
  

   admirable 
  treatises 
  of 
  Prof. 
  H. 
  P. 
  Gushing. 
  

  

  So 
  far 
  as 
  known 
  the 
  oldest 
  rocks 
  of 
  the 
  Adirondacks 
  are 
  those 
  

   of 
  Grenville 
  (Precambric) 
  age. 
  They 
  are 
  sedimentary 
  rocks, 
  

   originally 
  shales, 
  sandstones 
  and 
  limestones, 
  which 
  have 
  been 
  

   highly 
  metamorphosed 
  into 
  gneisses 
  and 
  crystalline 
  Hmestone. 
  

   These 
  rocks 
  are 
  of 
  unknown 
  but 
  great 
  thickness, 
  and 
  are 
  widely 
  

   scattered 
  throughout 
  the 
  Adirondacks, 
  thus 
  showing 
  that 
  the 
  

   whole 
  region 
  was 
  under 
  water 
  at 
  the 
  time 
  of 
  their 
  deposition. 
  

  

  After 
  the 
  deposition 
  of 
  the 
  Grenville 
  sediments 
  the 
  region 
  

   was 
  raised 
  above 
  the 
  ocean 
  level 
  and 
  the 
  rocks 
  began 
  to 
  decom- 
  

   pose 
  and 
  suffer 
  erosion. 
  Either 
  just 
  before, 
  during, 
  or 
  after 
  the 
  

   uplift, 
  great 
  masses 
  of 
  igneous 
  rocks 
  were 
  intruded. 
  The 
  Gren- 
  

   ville 
  rocks 
  were 
  for 
  the 
  most 
  part 
  engulfed 
  by 
  the 
  intrusion 
  so 
  

   that 
  only 
  occasional 
  patches 
  of 
  them 
  were 
  left 
  intact. 
  

  

  After 
  the 
  igneous 
  activity 
  the 
  rocks 
  became 
  thoroughly 
  meta- 
  

   morphosed 
  by 
  being 
  squeezed, 
  highly 
  folded 
  and 
  converted 
  into 
  

   gneisses. 
  Such 
  changes 
  can 
  take 
  place 
  only 
  at 
  great 
  depths 
  

   (several 
  thousand 
  feet) 
  and 
  hence 
  we 
  are 
  led 
  to 
  the 
  belief 
  that 
  

   a 
  vast 
  erosion 
  of 
  the 
  original 
  land 
  masses 
  must 
  have 
  taken 
  place. 
  

   This 
  in 
  turn 
  signifies 
  that 
  the 
  land 
  masses 
  must 
  have 
  remained 
  

   above 
  sea 
  level 
  for 
  an 
  immense 
  length 
  of 
  time. 
  

  

  At 
  or 
  toward 
  the 
  close 
  of 
  this 
  long 
  period 
  of 
  erosion, 
  igneous 
  

   activity 
  of 
  a 
  minor 
  character 
  took 
  place. 
  The 
  basic 
  igneous 
  

   rocks 
  erupted 
  at 
  this 
  time 
  are 
  especially 
  well 
  shown 
  in 
  the 
  

   northeastern 
  Adirondacks, 
  where 
  they 
  were 
  squeezed 
  up 
  

   between 
  joint 
  planes 
  in 
  the 
  older 
  rocks. 
  That 
  these 
  rocks 
  are 
  

   much 
  younger 
  than 
  the 
  igneous 
  rocks 
  first 
  mentioned 
  is 
  clearly 
  

   shown 
  by 
  their 
  mode 
  of 
  occurrence 
  and 
  their 
  general 
  lack 
  of 
  

   metamorphism. 
  

  

  Toward 
  the 
  close 
  of 
  the 
  erosion 
  period 
  the 
  region 
  of 
  the 
  

   Adirondacks 
  was 
  nearer 
  the 
  sea 
  level 
  and 
  of 
  slighter 
  relief 
  than 
  

   at 
  present. 
  Then 
  the 
  whole 
  region 
  began 
  to 
  sink 
  slowly, 
  allow- 
  

   ing 
  the 
  sea 
  to 
  encroach 
  upon 
  the 
  land 
  until 
  only 
  an 
  island 
  was 
  

   left 
  or 
  probably 
  even 
  until 
  the 
  whole 
  region 
  was 
  under 
  water. 
  

   During 
  the 
  subsidence, 
  deposition 
  of 
  Paleozoic 
  sediments 
  went 
  

  

  