﻿;6 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  SUMMARY 
  OF 
  GEOLOGICAL 
  HISTORY 
  

  

  A 
  brief 
  outline 
  of 
  the 
  geological 
  history 
  of 
  the 
  portion 
  of 
  the 
  

   Adirondacks 
  covered 
  by 
  the 
  North 
  Creek 
  sheet 
  is 
  here 
  given 
  in 
  

   order 
  to 
  bring 
  together 
  the 
  principal 
  events 
  of 
  that 
  history 
  in 
  the 
  

   regular 
  order 
  of 
  their 
  occurrence 
  so 
  far 
  as 
  known. 
  

  

  The 
  oldest 
  known 
  records 
  of 
  the 
  region 
  are 
  written 
  in 
  the 
  Gren- 
  

   ville 
  rocks 
  which, 
  by 
  their 
  very 
  character 
  and 
  composition, 
  are 
  

   undoubted 
  metamorphosed 
  sediments. 
  Because 
  of 
  the 
  great 
  thick- 
  

   ness 
  and 
  widespread 
  distribution 
  of 
  these 
  strata 
  in 
  New 
  York 
  and 
  

   Canada, 
  we 
  know 
  they 
  were 
  deposited 
  in 
  an 
  extensive 
  ocean 
  and 
  

   that 
  the 
  length 
  of 
  time 
  required 
  for 
  this 
  sedimentation 
  must 
  have 
  

   been 
  at 
  least 
  some 
  millions 
  of 
  years. 
  While 
  it 
  is 
  as 
  yet 
  impossible 
  

   definitely 
  to 
  classify 
  the 
  Grenville 
  with 
  either 
  the 
  Archean 
  or 
  Al- 
  

   gonkian 
  (Proterozoic), 
  the 
  evidence 
  is 
  decidedly 
  against 
  its 
  late 
  

   Precambric 
  age. 
  

  

  After 
  the 
  deposition 
  of 
  the 
  Grenville 
  sediments, 
  the 
  whole 
  Adi- 
  

   rondack 
  region, 
  including 
  the 
  area 
  of 
  the 
  North 
  Creek 
  sheet, 
  was 
  

   elevated 
  well 
  above 
  sea 
  level. 
  At 
  this 
  time 
  the 
  Grenville 
  strata 
  

   were 
  probably 
  folded. 
  Great 
  masses 
  of 
  molten 
  rock, 
  now 
  repre- 
  

   sented 
  by 
  the 
  syenite, 
  granite, 
  and 
  granite 
  porphyry, 
  were 
  intruded 
  

   just 
  before, 
  during, 
  or 
  after 
  the 
  uplift, 
  the 
  most 
  reasonable 
  view 
  

   being 
  that 
  the 
  intrusion 
  occurred 
  during 
  the 
  uplift 
  because 
  the 
  same 
  

   great 
  pressure 
  could 
  well 
  have 
  pushed 
  up 
  the 
  molten 
  masses 
  during 
  

   the 
  process 
  of 
  elevation. 
  In 
  some 
  cases 
  the 
  Grenville 
  appears 
  to 
  

   have 
  been 
  pushed 
  upward 
  and 
  to 
  have 
  been 
  largely 
  removed 
  by 
  

   erosion 
  since 
  ; 
  in 
  other 
  cases 
  the 
  Grenville 
  was 
  more 
  or 
  less 
  engulfed 
  

   by, 
  or 
  involved 
  with, 
  the 
  molten 
  flood 
  as 
  shown 
  by 
  the 
  numerous 
  

   Grenville 
  inclusions 
  and 
  the 
  areas 
  of 
  mixed 
  gneisses 
  ; 
  while 
  in 
  still 
  

   other 
  cases 
  the 
  Grenville 
  rocks 
  were 
  left 
  practically 
  intact 
  as 
  shown 
  

   by 
  the 
  large 
  Grenville 
  areas. 
  These 
  intrusives 
  now 
  exposed 
  at 
  the 
  

   surface 
  were, 
  at 
  the 
  time 
  of 
  their 
  intrusion, 
  deeply 
  buried 
  under 
  

   a 
  great 
  thickness 
  of 
  overlying 
  rock 
  material. 
  This 
  we 
  know 
  because 
  

   they 
  are 
  true 
  plutonic 
  rocks 
  which 
  could 
  have 
  cooled 
  only 
  under 
  

   such 
  conditions. 
  The 
  vast 
  amount 
  of 
  erosion 
  since 
  their 
  intrusion 
  

   has 
  exposed 
  them. 
  

  

  Following 
  this 
  great 
  period 
  of 
  igneous 
  intrusion 
  there 
  was 
  a 
  

   time 
  of 
  minor 
  igneous 
  activity 
  when 
  the 
  gabbros, 
  in 
  molten 
  condi- 
  

   tion, 
  were 
  forced 
  upward 
  into 
  the 
  crust 
  of 
  the 
  earth. 
  Since 
  the 
  

   gabbros 
  now 
  exposed 
  at 
  the 
  surface 
  are 
  true 
  plutonic 
  rocks 
  they 
  

   too 
  must 
  have 
  been 
  deeply 
  buried 
  under 
  material 
  which 
  has 
  been 
  

   removed 
  by 
  erosion. 
  

  

  