﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  39 
  

  

  that 
  many 
  thousands 
  of 
  feet 
  of 
  materials 
  have 
  'been' 
  removed 
  by 
  

   erosion 
  in 
  order 
  to 
  expose 
  the 
  present 
  rocks 
  to 
  view 
  does 
  not 
  neces- 
  

   sarily 
  imply 
  that 
  the 
  mountains 
  at 
  any 
  time 
  had 
  so 
  great 
  a 
  height 
  be- 
  

   cause 
  it 
  is 
  possible 
  that, 
  while 
  elevation 
  slowly 
  progressed, 
  material 
  

   was 
  steadily 
  removed 
  by 
  the 
  process 
  of 
  erosion. 
  All 
  our 
  knowledge 
  

   regarding 
  later 
  and 
  better 
  known 
  mountains, 
  however, 
  leaves 
  little 
  

   doubt 
  that 
  those 
  first 
  Adirondacks 
  were 
  mountains 
  vastly 
  higher 
  

   than 
  those 
  of 
  today. 
  

  

  The 
  same 
  sort 
  of 
  uplift 
  and 
  succeeding 
  profound 
  erosion 
  also 
  

   affected 
  the 
  present 
  region 
  of 
  the 
  Hudson 
  Highlands 
  (see 
  figure 
  

   14) 
  and, 
  this 
  being 
  the 
  case, 
  we 
  can 
  state 
  with 
  confidence 
  that 
  

   much, 
  if 
  not 
  all, 
  of 
  northern 
  and 
  eastern 
  New 
  York 
  was 
  in- 
  

   volved 
  in 
  this 
  mountain-making 
  process. 
  For 
  western 
  New 
  York 
  

   the 
  physical 
  geography 
  of 
  this 
  time 
  has 
  not 
  been 
  determined 
  because 
  

   all 
  that 
  region 
  is 
  so 
  deeply 
  buried 
  under 
  the 
  Paleozoic 
  strata. 
  

  

  LATE 
  PRECAMBRIC 
  HISTORY 
  

  

  The 
  fact 
  that 
  such 
  a 
  great 
  thickness 
  of 
  rock 
  was 
  removed 
  by 
  ero- 
  

   sion 
  implies 
  a 
  vast 
  length 
  of 
  time 
  for 
  the 
  accomplishment 
  of 
  that 
  

   work. 
  According 
  to 
  all 
  that 
  we 
  know 
  regarding 
  the 
  rates 
  of 
  erosion 
  

   of 
  mountains 
  of 
  the 
  present 
  and 
  past, 
  the 
  erosion 
  of 
  the 
  Adiron- 
  

   dacks 
  must 
  have 
  extended 
  over 
  a 
  period 
  of 
  at 
  least 
  several 
  mil- 
  

   lion 
  years. 
  When 
  we 
  consider 
  that, 
  at 
  the 
  opening 
  of 
  Upper 
  Cam- 
  

   bric 
  time, 
  most 
  of 
  the 
  region 
  had 
  been 
  worn 
  down 
  to 
  the 
  condition 
  

   of 
  a 
  peneplain 
  (see 
  page 
  42), 
  we 
  are 
  confident 
  that 
  no 
  small 
  

   amount 
  of 
  the 
  erosion 
  was 
  accomplished 
  even 
  before 
  the 
  opening 
  

   of 
  the 
  Paleozoic 
  era, 
  and 
  that 
  it 
  continued 
  well 
  into 
  the 
  early 
  Paleo- 
  

   zoic. 
  The 
  whole 
  problem 
  of 
  this 
  later 
  erosion 
  and 
  its 
  effects 
  will 
  be 
  

   treated 
  in 
  the 
  next 
  chapter. 
  

  

  Well 
  toward 
  the 
  end 
  of 
  Precambric 
  time, 
  igneous 
  activity 
  of 
  a 
  

   minor 
  character 
  took 
  place 
  in 
  the 
  formation 
  of 
  dikes 
  which, 
  as 
  we 
  

   have 
  learned, 
  are 
  fissures 
  in 
  the 
  crust 
  of 
  the 
  earth 
  which 
  have 
  been 
  

   filled 
  with 
  molten 
  rock. 
  In 
  the 
  Adirondack 
  region 
  there 
  are 
  sev- 
  

   eral 
  kinds 
  of 
  dike 
  rocks, 
  the 
  most 
  common 
  being 
  pegmatite 
  and 
  dia- 
  

   base. 
  Pegmatite 
  is 
  a 
  very 
  coarse-grained, 
  light 
  colored 
  rock 
  of 
  gen- 
  

   eral 
  granitic 
  composition, 
  the 
  feldspar 
  and 
  quartz 
  crystals 
  often 
  at- 
  

   taining 
  lengths 
  of 
  several 
  inches 
  to 
  a 
  foot. 
  Diabase 
  is 
  a 
  fine-grained 
  

   rock 
  much 
  like 
  ordinary 
  basaltic 
  lava. 
  These 
  dikes 
  are 
  generally 
  

   less 
  than 
  a 
  mile 
  long 
  and 
  comparatively 
  narrow. 
  That 
  they 
  are 
  

   younger 
  than 
  the 
  other 
  igneous 
  rocks 
  of 
  the 
  region 
  is 
  abundantly 
  

   proved 
  by 
  the 
  fact 
  that 
  they 
  cut 
  through 
  those 
  rocks 
  in 
  many 
  places 
  

  

  