﻿30 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  In 
  the 
  particular 
  area 
  where 
  this 
  rock 
  has 
  its 
  greatest 
  extent 
  it 
  has 
  

   been 
  subjected 
  to 
  greater 
  dynamic 
  action 
  than 
  elsewhere 
  and 
  has 
  

   been 
  reduced 
  to 
  a 
  gneissoid 
  condition. 
  

  

  The 
  persistence 
  of 
  reddish 
  orthoclase 
  in 
  this 
  rock 
  suggests 
  that 
  

   it 
  has 
  sprung 
  from 
  a 
  common 
  source 
  with 
  the 
  numerous 
  dykes 
  of 
  

   red 
  pegmatite 
  and 
  granite 
  of 
  similar 
  composition 
  which 
  penetrate 
  

   the 
  schist 
  and 
  limestone 
  in 
  many 
  points 
  in 
  Westchester 
  county. 
  

  

  GRANITES. 
  

  

  Gray 
  and 
  reddish 
  granites 
  in 
  small 
  dykes 
  oblique 
  to 
  the 
  banding 
  of 
  

   the 
  gneiss 
  and 
  schists 
  are 
  quite 
  abundant, 
  but 
  of 
  more 
  frequent 
  occur- 
  

   rence 
  are 
  lenses 
  and 
  injections 
  of 
  granite 
  and 
  pegmatite 
  parallel 
  to 
  

   the 
  banding 
  of 
  the 
  schistosity. 
  Bosses 
  of 
  pegmatite 
  frequently 
  occur 
  

   in 
  the 
  Manhattan 
  schist. 
  A 
  granite 
  area 
  of 
  considerable 
  size 
  occurs 
  

   near 
  Union 
  Corners 
  and 
  many 
  have 
  been 
  found 
  on 
  New 
  York 
  Is- 
  

   land, 
  which 
  are 
  now 
  built 
  over 
  and 
  concealed 
  from 
  view. 
  The 
  small 
  

   islands 
  and 
  reefs 
  in 
  the 
  upper 
  Bay 
  and 
  most 
  of 
  those 
  in 
  Long 
  Island 
  

   Sound 
  owe 
  their 
  existence 
  to 
  intrusions 
  of 
  granite 
  and 
  other 
  erup* 
  

   tives 
  in 
  the 
  schist. 
  

  

  PEGMATITE 
  DYKES 
  AND 
  BOSSES. 
  

   These 
  are 
  intrusions 
  of 
  coarse 
  granitic 
  material 
  in 
  dykes 
  and 
  

   bosses 
  from 
  one 
  to 
  ten 
  feet 
  in 
  diameter. 
  They 
  are 
  most 
  abundant 
  

   in 
  the 
  Manhattan 
  schist. 
  

  

  HARRISON 
  DIORITE.* 
  

  

  This 
  rock 
  is 
  intrusive 
  in 
  the 
  Manhattan 
  schist 
  in 
  the 
  town 
  of 
  Har.- 
  

   rison 
  and 
  consists 
  of 
  orthoclase, 
  plagioclase, 
  quartz 
  and 
  hornblende. 
  

   A 
  smaller 
  area 
  of 
  similar 
  rock 
  occurs 
  at 
  Ravenswood, 
  L. 
  L, 
  where 
  

   it 
  outcrops 
  in 
  a 
  long 
  narrow 
  ridge 
  of 
  northeasterly 
  trend 
  and 
  is 
  

   intrusive 
  in 
  the 
  Fordham 
  gneiss. 
  

  

  The 
  mass 
  which 
  forms 
  Milton 
  Point 
  near 
  Rye 
  has 
  been 
  subjected 
  

   to 
  much 
  dynamic 
  action 
  and 
  is 
  well 
  banded. 
  The 
  same 
  rock 
  is 
  

   abundant 
  along 
  the 
  shore 
  of 
  Long 
  Island 
  Sound 
  between 
  Portchester 
  

   and 
  Greenwich. 
  

  

  * 
  H. 
  Ries 
  Trans. 
  N. 
  Y. 
  Acad. 
  Sci. 
  1895 
  Vol. 
  xiv 
  pp 
  80-86. 
  

  

  