﻿48 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Alexandria 
  bathylith, 
  though 
  tliere 
  is 
  a 
  zone 
  between 
  the 
  two 
  in 
  

   which 
  exposures 
  are 
  poor 
  and 
  infrequent. 
  They 
  are 
  separated 
  

   from 
  one 
  another 
  in 
  part 
  by 
  tongues 
  of 
  Potsdam 
  sandstone, 
  and 
  

   in 
  part 
  by 
  low, 
  marshy 
  valleys 
  in 
  which 
  no 
  rock 
  outcrops 
  appear. 
  

   The 
  exposures, 
  however, 
  cover 
  an 
  area 
  of 
  several 
  square 
  miles, 
  and 
  

   extend 
  to 
  a 
  distance 
  of 
  at 
  least 
  3 
  miles 
  from 
  the 
  edge 
  of 
  the 
  bathy- 
  

   lith. 
  The 
  schists 
  are 
  everywhere 
  cut 
  by 
  dikes 
  of 
  granite, 
  most 
  

   numerously 
  as 
  the 
  granite 
  is 
  approached. 
  While 
  chiefly 
  of 
  the 
  Alex- 
  

   andria 
  granite 
  gneiss, 
  it 
  seems 
  to 
  us 
  that 
  dikes 
  of 
  the 
  Picton 
  gran- 
  

   ite 
  are 
  also 
  present 
  numerously, 
  though 
  it 
  is 
  cHfficult 
  to 
  arrive 
  at 
  

   certainty 
  in 
  the 
  matter. 
  Certainly 
  they 
  are 
  present 
  in 
  the 
  granite 
  

   gneiss 
  itself. 
  Nowhere 
  else 
  in 
  northern 
  New 
  York 
  have 
  we 
  seen 
  

   just 
  this 
  type 
  of 
  schists, 
  except 
  as 
  occasional 
  occurrences 
  of 
  small 
  

   extent 
  and 
  bulk. 
  We 
  are 
  disposed 
  to 
  regard 
  them 
  as 
  contact 
  rocks, 
  

   produced 
  by 
  the 
  action 
  of 
  the 
  granite 
  upon 
  what 
  wxre, 
  prior 
  to 
  the 
  

   intrusion, 
  somewhat 
  impure 
  limestones. 
  We 
  are 
  disposed 
  also 
  to 
  re- 
  

   gard 
  the 
  Picton 
  granite 
  dikes 
  as 
  especially 
  influential 
  in 
  the 
  action. 
  

   It 
  must 
  be 
  frankly 
  stated, 
  however, 
  that 
  there 
  are 
  certain 
  difficul- 
  

   ties 
  in 
  the 
  way 
  of 
  this 
  view, 
  and 
  they 
  will 
  be 
  later 
  summed 
  up. 
  

  

  The 
  schists 
  are 
  well 
  banded 
  and 
  foliated 
  and 
  range 
  from 
  light 
  

   to 
  dark 
  green, 
  or 
  greenish 
  black, 
  in 
  color. 
  They 
  are 
  usually 
  of 
  

   finely 
  granular 
  texture 
  though 
  these 
  alternate 
  wath 
  somewhat 
  

   coarser 
  grained 
  bands. 
  These 
  latter 
  show 
  poorer 
  foliation 
  and 
  are 
  

   mottled 
  green 
  and 
  pink 
  in 
  color. 
  Narrow, 
  dark 
  red 
  bands 
  some- 
  

   times 
  appear, 
  due 
  to 
  subsequent 
  infiltration 
  of 
  ferric 
  oxid. 
  At 
  

   times 
  the 
  green 
  minerals 
  become 
  scant, 
  and 
  the 
  rock 
  then 
  has 
  a 
  

   light 
  red 
  to 
  pink 
  shade. 
  Narrow 
  bands 
  of 
  black 
  amphibolite 
  and 
  

   of 
  finely 
  micaceous 
  schist 
  also 
  appear, 
  and 
  an 
  occasional 
  thin 
  quartz- 
  

   ite 
  band. 
  But 
  the 
  bulk 
  of 
  the 
  series 
  is 
  of 
  green 
  schist. 
  Granite 
  

   dikes 
  and 
  dikelets 
  abound 
  everywhere, 
  cutting 
  across 
  or 
  parallel 
  

   with 
  the 
  bedding, 
  in 
  the 
  latter 
  case 
  often 
  forming 
  a 
  good 
  injection 
  

   gneiss. 
  The 
  dikes 
  are 
  of 
  fine, 
  granite 
  gneiss, 
  of 
  coarse 
  granite, 
  

   of 
  yet 
  coarser 
  granite 
  pegmatite, 
  or 
  of 
  quartz, 
  the 
  first 
  most 
  abund- 
  

   ant. 
  

  

  In 
  composition 
  these 
  green 
  schists 
  are 
  essentially 
  feldspar-pyrox- 
  

   ene 
  rocks, 
  the 
  latter 
  of 
  green 
  color 
  and 
  responsible 
  for 
  the 
  general 
  

   hue 
  of 
  the 
  rock. 
  x\ctinolite 
  is 
  commonly 
  present, 
  and 
  very 
  abund- 
  

   ant 
  in 
  some 
  of 
  the 
  bands 
  ; 
  it 
  is 
  the 
  only 
  amphibole 
  noted 
  in 
  the 
  

   schists, 
  except 
  in 
  the 
  occasional 
  amphibolite 
  bands. 
  Epidote 
  is 
  

   often 
  present, 
  though 
  far 
  less 
  common 
  than 
  the 
  actinolite. 
  Some 
  

   layers 
  hold 
  frequent, 
  small, 
  light 
  colored 
  garnets. 
  Small, 
  scattered, 
  

   black 
  tourmalins 
  occur 
  throughout 
  the 
  rock 
  in 
  all 
  exposures. 
  

  

  