﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  49 
  

  

  chiding 
  the 
  great 
  Taconic 
  mountains) 
  was 
  dry 
  land 
  toward 
  the 
  

   close 
  of 
  the 
  Ordovicic 
  period, 
  while 
  the 
  physical 
  geography 
  of 
  

   western 
  New 
  York 
  for 
  that 
  time 
  is 
  not 
  certainly 
  known. 
  

  

  It 
  should 
  'be 
  noted 
  in 
  passing 
  that 
  the 
  rocks 
  of 
  the 
  Highlands-of- 
  

   the-Hudson 
  were, 
  for 
  a 
  second 
  time, 
  clearly 
  involved 
  in 
  mountain- 
  

   making 
  disturbances. 
  The 
  structural 
  features 
  of 
  the 
  Taconic 
  moun- 
  

   tains 
  are 
  finely 
  exhibited 
  in 
  southeastern 
  New 
  York 
  from 
  Pough- 
  

   keepsie 
  to 
  New 
  York 
  City, 
  where 
  one 
  literally 
  passes 
  across 
  the 
  

   roots 
  of 
  the 
  former 
  great 
  range. 
  The 
  distinct 
  northeast-southwest 
  

   trend 
  of 
  the 
  topographic 
  relief 
  in 
  this 
  part 
  of 
  the 
  State 
  is 
  due 
  to 
  the 
  

   .fact 
  that 
  the 
  relief 
  is 
  still 
  largely 
  controlled 
  by 
  the 
  Taconic 
  folds 
  

   and 
  faults. 
  The 
  Hudson 
  river 
  has 
  cut 
  a 
  deep 
  channel 
  across 
  these 
  

   structure 
  lines, 
  and 
  along 
  its 
  banks 
  excellent 
  opportunity 
  is 
  afforded 
  

   for 
  the 
  study 
  of 
  the 
  rocks, 
  folds, 
  faults 
  etc. 
  

  

  Another 
  feature 
  which 
  must 
  not 
  be 
  overlooked 
  is 
  the 
  profound 
  

   metamorphism 
  of 
  the 
  strata 
  along 
  the 
  main 
  axis 
  of 
  the 
  range. 
  The 
  

   very 
  intense 
  compression, 
  under 
  very 
  high 
  moist 
  heat, 
  caused 
  the 
  

   deeply 
  buried 
  strata 
  along 
  the 
  main 
  axis 
  of 
  uplift 
  to 
  become 
  rather 
  

   plastic, 
  and 
  hence 
  the 
  sediments 
  became 
  more 
  or 
  less 
  foliated 
  and 
  

   crystallized 
  into 
  the 
  various 
  metamorphic 
  rock 
  types, 
  the 
  limestone 
  

   becoming 
  marble, 
  the 
  shale 
  becoming 
  slate 
  or 
  schist, 
  and 
  the 
  sand- 
  

   stone 
  becoming 
  quartzite. 
  Thus 
  we 
  have 
  extensive 
  marble 
  quarries 
  

   in 
  southern 
  Vermont, 
  the 
  slate 
  in 
  the 
  quarries 
  of 
  Washington 
  

   county, 
  New 
  York, 
  and 
  the 
  Berkshire 
  schist 
  in 
  the 
  Berkshire 
  hills 
  

   of 
  Massachusetts. 
  In 
  passing 
  down 
  the 
  Hudson 
  river 
  from 
  King- 
  

   ston 
  to 
  New 
  York 
  City, 
  the 
  several 
  stages 
  in 
  the 
  metamorphism 
  of 
  

   the 
  Ordovicic 
  slate 
  formation 
  are 
  finely 
  illustrated. 
  Thus, 
  from 
  

   Kingston 
  to 
  near 
  Poughkeepsie 
  the 
  strata 
  are 
  distinctly 
  folded 
  but 
  

   not 
  metamorphosed 
  ; 
  from 
  Poughkeepsie 
  to 
  the 
  Highlands, 
  the 
  

   strata 
  are 
  highly 
  folded 
  and 
  partially 
  metamorphosed, 
  the 
  shale 
  lay- 
  

   ers 
  nearly 
  always 
  having 
  been 
  changed 
  to 
  slate, 
  while 
  the 
  associated 
  

   and 
  more 
  resistant 
  sandstone 
  layers 
  have 
  escaped 
  change 
  ; 
  from 
  

   the 
  Highlands 
  to 
  New 
  York 
  City 
  the 
  rocks 
  have 
  been 
  highly 
  folded 
  

   and 
  metamorphosed, 
  both 
  shale 
  and 
  sandstone 
  having 
  been 
  con- 
  

   verted 
  into 
  schist 
  locally 
  called 
  the 
  Manhattan 
  schist. 
  For 
  example, 
  

   the 
  rocks 
  exposed 
  in 
  Central 
  Park 
  are 
  Manhattan 
  schists 
  which 
  are 
  

   believed 
  to 
  have 
  been 
  originally 
  Hudson 
  River 
  shales 
  and 
  sandstones 
  

   which 
  have 
  become 
  thoroughly 
  crystallized 
  bv 
  intense 
  meta- 
  

   morphism. 
  1 
  

  

  1 
  Professor 
  Berkey 
  has 
  recently 
  suggested 
  the 
  possibility 
  that 
  the 
  Man- 
  

   hattan 
  schist 
  may 
  be 
  Precambric 
  in 
  age; 
  if 
  so, 
  the 
  latter 
  part 
  of 
  this 
  state- 
  

   ment 
  does 
  not 
  apply. 
  

  

  