﻿34 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  abundance. 
  Frequent 
  bands 
  of 
  it 
  occur 
  within 
  the 
  Grenville 
  series, 
  

   but 
  these 
  are 
  usually 
  of 
  no 
  great 
  thickness. 
  There 
  is 
  but 
  little 
  of 
  

   the 
  rock 
  present 
  to 
  which 
  an 
  igneous 
  origin 
  may 
  be 
  definitely 
  as- 
  

   signed. 
  There 
  are 
  small 
  areas 
  of 
  such 
  rock 
  in 
  the 
  district 
  north 
  ind 
  

   northeast 
  of 
  Theresa, 
  where 
  a 
  somewhat 
  more 
  heavily 
  bedded 
  am- 
  

   phibolite 
  occurs, 
  which 
  holds 
  much 
  pyroxene 
  in 
  addition 
  to 
  the 
  

   hornblende, 
  and 
  which 
  seems 
  to 
  definitely 
  cut 
  the 
  limestone 
  with 
  

   which 
  it 
  is 
  associated. 
  There 
  are, 
  however, 
  amphibolite 
  bands 
  in- 
  

   terstratified 
  with 
  the 
  same 
  limestone, 
  and 
  the 
  mass 
  has 
  been 
  severely 
  

   deformed, 
  with 
  the 
  production 
  of 
  flow 
  in 
  the 
  limestone 
  and 
  the 
  

   fracturing 
  of 
  the 
  amphibolite 
  into 
  blocks, 
  making 
  one 
  appear 
  to 
  

   cut 
  and 
  be 
  included 
  in 
  the 
  other, 
  but 
  this 
  does 
  not 
  seem 
  to 
  be 
  a 
  

   case 
  of 
  the 
  sort. 
  In 
  our 
  experience 
  amphibolites 
  which 
  result 
  from 
  

   the 
  metamorphism 
  of 
  gabbro^ 
  usually 
  contain 
  pyroxene 
  in 
  quantity, 
  

   while 
  those 
  originating 
  from 
  calcareous 
  shales 
  are 
  more 
  apt 
  to 
  be 
  

   micaceous 
  and 
  lack 
  the 
  pyroxene, 
  but 
  this 
  is 
  far 
  from 
  being 
  an 
  in- 
  

   variable 
  rule, 
  and 
  is 
  only 
  suggestive 
  of 
  origin, 
  not 
  demonstrative. 
  

  

  The 
  amphibolites 
  interstratified 
  within 
  the 
  Grenville 
  series, 
  and 
  

   regarded 
  as 
  metamorphosed 
  sediments, 
  calcareous 
  shales 
  or 
  some- 
  

   thing 
  of 
  that 
  sort, 
  are 
  mostly 
  quite 
  finely 
  and 
  evenly 
  granular 
  rocks, 
  

   which 
  have 
  wholly 
  recrystallized, 
  and 
  vary 
  from 
  very 
  solid 
  look- 
  

   ing, 
  dense 
  rocks 
  in 
  which 
  mica 
  is 
  but 
  sparingly 
  present, 
  to 
  very 
  

   schistose, 
  highly 
  micaceous 
  rocks, 
  which 
  rapidly 
  break 
  down 
  under 
  

   the 
  weather. 
  In 
  most 
  of 
  these 
  ortlioclase 
  feldspar 
  is 
  apt 
  to 
  predomi- 
  

   nate 
  over 
  plagioclase, 
  and 
  much 
  of 
  the 
  rock 
  contains 
  some 
  quartz, 
  

   the 
  micaceous 
  varieties 
  often 
  considerable. 
  The 
  manner 
  in 
  which 
  

   the 
  variations 
  appear 
  is 
  itself 
  highly 
  suggestive 
  of 
  metamorphosed 
  

   sediments 
  which 
  differed 
  somewhat 
  in 
  character 
  from 
  bed 
  to 
  bed. 
  

   Some 
  of 
  the 
  rock 
  contains 
  garnets, 
  in 
  some 
  cases 
  reaching 
  large 
  

   size, 
  but 
  they 
  are 
  exceptional 
  rather 
  than 
  the 
  rule. 
  

  

  The 
  amphibolite 
  of 
  contact 
  origin 
  will 
  be 
  discussed 
  under 
  the 
  

   general 
  topic 
  of 
  contact 
  rocks. 
  

  

  Schists. 
  Under 
  this 
  heading 
  are 
  included 
  a 
  large 
  number 
  of 
  

   rock 
  types, 
  so 
  many 
  that 
  it 
  seems 
  hopeless 
  to 
  attempt 
  to 
  describe 
  

   all, 
  or 
  many 
  of 
  them. 
  No 
  doubt 
  they 
  have 
  diverse 
  origins. 
  Some 
  

   of 
  them 
  quite 
  certainly 
  owe 
  their 
  present 
  character 
  to 
  contact 
  action, 
  

   and 
  no 
  doubt 
  contact 
  action 
  of 
  varying 
  kind, 
  and 
  in 
  varying 
  degree, 
  

   is 
  in 
  large 
  measure 
  responsible 
  for 
  the 
  great 
  diversity 
  of 
  the 
  group. 
  

   Some 
  of 
  the 
  rocks 
  grouped 
  here 
  are 
  no 
  doubt 
  igneous, 
  and 
  in 
  their 
  

   character 
  distinctly 
  suggest 
  such 
  an 
  origin, 
  though 
  the 
  proof 
  is 
  dif- 
  

   ficult 
  to 
  obtain. 
  

  

  A 
  very 
  common 
  variety 
  of 
  Grenville 
  schist, 
  the 
  so 
  called 
  " 
  rusty 
  

  

  