﻿24 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  of 
  Grenville 
  gneisses, 
  with 
  these 
  rocks, 
  in 
  turn, 
  grading 
  into 
  pure 
  

   biotite-garnet 
  and 
  quartzitic 
  Grenville 
  gneisses 
  at 
  the 
  base 
  of 
  the 
  

   mountain. 
  Thus 
  we 
  have 
  a 
  perfect 
  transition 
  from 
  the 
  gray, 
  gran- 
  

   itic 
  rock 
  into 
  the 
  granite 
  porphyry, 
  on 
  the 
  one 
  hand, 
  and 
  into 
  the 
  

   Grenville 
  on 
  the 
  other 
  so 
  that 
  there 
  appears 
  to 
  be 
  no 
  escape 
  from 
  

   the 
  idea 
  that 
  these 
  gray, 
  granitic 
  rocks 
  were 
  formed 
  by 
  actual 
  

   fusion 
  and 
  incorporation 
  of 
  more 
  or 
  less 
  of 
  the 
  Grenville 
  into 
  the 
  

   granite 
  porphyry 
  magma. 
  The 
  presence 
  of 
  the 
  inclusions 
  does 
  not 
  

   necessarily 
  oppose 
  this 
  view 
  because 
  they 
  may 
  well 
  enough 
  simply 
  

   represent 
  fragments 
  of 
  Grenville 
  which 
  were 
  caught 
  in 
  the 
  granite 
  

   magma 
  just 
  before 
  consolidation 
  or 
  when 
  the 
  temperature 
  was 
  not 
  

   high 
  enough 
  actually 
  to 
  melt 
  the 
  fragments. 
  Gray 
  granitic 
  rocks 
  

   of 
  apparently 
  the 
  same 
  origin 
  are 
  common 
  throughout 
  this 
  mixed 
  

   gneiss 
  area. 
  

  

  Another 
  interesting 
  mixed 
  gneiss 
  area 
  is 
  the 
  one 
  just 
  north 
  of 
  

   the 
  village 
  of 
  Horicon. 
  In 
  the 
  vicinity 
  of 
  the 
  quarry, 
  at 
  the 
  base 
  

   of 
  the 
  mountain, 
  the 
  rock 
  is 
  very 
  typical 
  granite 
  porphyry 
  which 
  

   contains 
  a 
  few 
  long, 
  narrow, 
  sharply 
  defined, 
  Grenville 
  gneiss 
  in- 
  

   clusions. 
  Going 
  up 
  the 
  mountain 
  side 
  from 
  the 
  quarry, 
  the 
  granite 
  

   porphyry, 
  which 
  at 
  times 
  (in 
  patches 
  or 
  wide 
  bands) 
  appears 
  typi- 
  

   cal, 
  is 
  intimately 
  associated 
  with 
  Grenville. 
  This 
  Grenville 
  occurs 
  

   as 
  large 
  and 
  small 
  inclusions, 
  often 
  sharply 
  defined 
  and 
  nearly 
  al- 
  

   ways 
  drawn 
  out 
  parallel 
  to 
  the 
  foliation. 
  The 
  included 
  rocks 
  are 
  

   chiefly 
  banded 
  biotitic, 
  hornblendic, 
  and 
  quartzitic 
  gneisses 
  often 
  

   in 
  bands 
  from 
  20 
  to 
  30 
  feet 
  wide. 
  Toward 
  the 
  top 
  of 
  the 
  moun- 
  

   tain 
  the 
  rock 
  is 
  mostly 
  like 
  the 
  gray 
  granitic 
  rock 
  already 
  de- 
  

   scribed 
  as 
  occurring 
  at 
  the 
  top 
  of 
  Prospect 
  mountain, 
  and 
  the 
  

   inclusions 
  are 
  fewer 
  and 
  not 
  so 
  sharply 
  defined. 
  Here 
  again 
  this 
  

   granitic 
  gneiss 
  appears 
  to 
  be 
  an 
  assimilation 
  product, 
  while 
  farther 
  

   down 
  the 
  mountain 
  side 
  the 
  temperature 
  seems 
  not 
  to 
  have 
  been 
  

   high 
  enough 
  to 
  cause 
  any 
  considerable 
  melting 
  or 
  assimilation 
  of 
  

   the 
  included 
  gneisses. 
  

  

  In 
  the 
  large, 
  mixed 
  gneiss 
  area 
  south 
  of 
  Henderson 
  mountain 
  

   there 
  are 
  many 
  fine 
  illustrations 
  of 
  very 
  intimately 
  associated 
  Gren- 
  

   ville 
  and 
  gray 
  granitic 
  rocks, 
  the 
  Grenville 
  often 
  having 
  been 
  more 
  

   or 
  less 
  melted 
  into 
  the 
  granites. 
  The 
  granites 
  predominate 
  and 
  

   some 
  of 
  them 
  at 
  least 
  are 
  thought 
  to 
  be 
  assimilation 
  products. 
  

   Such 
  phenomena 
  are 
  well 
  exhibited 
  from 
  Igerna 
  southwestward 
  to 
  

   the 
  river. 
  

  

  In 
  the 
  mixed 
  gneiss 
  area 
  which 
  borders 
  the 
  Chase-Kelm 
  moun- 
  

   tain 
  granite 
  porphyry 
  mass 
  on 
  the 
  west, 
  the 
  prevailing 
  rock 
  is 
  a 
  

  

  