﻿IO 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  A 
  patch 
  of 
  Grenville 
  gneiss 
  lies 
  at 
  the 
  extreme 
  northwestern 
  

   corner 
  of 
  the 
  sheet 
  and 
  another 
  at 
  the 
  northeastern 
  corner, 
  while 
  

   a 
  belt 
  of 
  limestone 
  just 
  enters 
  the 
  northern 
  map 
  limit 
  at 
  the 
  Nat- 
  

   ural 
  Bridge. 
  The 
  Grenville 
  around 
  Loon 
  lake 
  consists 
  mostly 
  of 
  

   white 
  to 
  gray 
  gneisses. 
  

  

  A 
  number 
  of 
  small 
  patches 
  of 
  Grenville 
  are 
  shown 
  within 
  the 
  

   igneous 
  rock 
  areas 
  and 
  these 
  usually 
  represent 
  actual 
  inclusions 
  

   of 
  the 
  Grenville 
  which 
  are 
  large 
  enough 
  to 
  be 
  indicated 
  on 
  the 
  

   map. 
  No 
  attempt 
  has 
  been 
  made 
  to 
  show 
  the 
  many 
  smaller 
  in- 
  

   clusions. 
  The 
  Grenville 
  occurring 
  within 
  the 
  areas 
  of 
  mixed 
  

   gneisses 
  will 
  be 
  discussed 
  in 
  connection 
  with 
  those 
  gneisses. 
  

  

  Grenville 
  types. 
  The 
  Grenville 
  types 
  are 
  described 
  in 
  consid- 
  

   erable 
  detail 
  because, 
  in 
  the 
  writer's 
  opinion, 
  if 
  the 
  broader 
  struc- 
  

   tural 
  and 
  stratigraphic 
  relations 
  of 
  the 
  Grenville 
  series 
  are 
  ever 
  

   to 
  be 
  worked 
  out, 
  it 
  is 
  necessary 
  to 
  have 
  these 
  rocks 
  carefully 
  

   descriped 
  and 
  mapped 
  over 
  a 
  much 
  larger 
  area 
  than 
  that 
  of 
  a 
  single 
  

   quadrangle. 
  When 
  a 
  number 
  of 
  the 
  other 
  quadrangles 
  of 
  the 
  south- 
  

   eastern 
  Adirondacks, 
  in 
  addition 
  to 
  those 
  of 
  Broadalbin, 
  Saratoga, 
  

   and 
  North 
  Creek 
  already 
  published 
  and 
  the 
  Lake 
  Pleasant 
  now 
  

   being 
  studied, 
  are 
  mapped 
  in 
  detail, 
  it 
  is 
  quite 
  possible 
  that 
  some 
  

   of 
  the 
  larger 
  structural 
  and 
  stratigraphic 
  features 
  may 
  be 
  made 
  

   out. 
  

  

  Crystalline 
  limestone. 
  In 
  common 
  with 
  the 
  Newcomb 
  and 
  the 
  

   southern 
  portion 
  of 
  the 
  Schroon 
  lake 
  sheets, 
  the 
  limestone 
  of 
  the 
  

   North 
  Creek 
  sheet 
  is 
  much 
  more 
  prominently 
  developed 
  than 
  is 
  

   usual 
  in 
  the 
  southeastern 
  Adirondacks. 
  The 
  numerous 
  outcrops 
  

   of 
  limestone 
  (actually 
  observed) 
  are 
  indicated 
  on 
  the 
  accompany- 
  

   ing 
  map. 
  

  

  Perhaps 
  the 
  most 
  abundant 
  variety 
  is 
  a 
  nearly 
  white, 
  medium 
  to 
  

   coarse 
  crystalline, 
  very 
  calcitic 
  limestone 
  through 
  which 
  are 
  scat- 
  

   tered 
  numerous 
  flakes 
  of 
  graphite 
  and 
  phlogopite 
  or 
  biotite 
  and 
  

   occasional 
  specks 
  of 
  pyrrhotite. 
  The 
  calcite 
  crystals 
  range 
  from 
  a 
  

   few 
  millimeters 
  to 
  more 
  than 
  a 
  half 
  inch 
  across, 
  while 
  the 
  graph- 
  

   ite 
  flakes 
  are 
  commonly 
  several 
  millimeters 
  across. 
  Other 
  crystals 
  

   less 
  often 
  seen 
  in 
  this 
  rock 
  are 
  pyrite, 
  nearly 
  colorless 
  pyroxene, 
  

   and 
  brown 
  tourmaline. 
  Rarely 
  the 
  limestone 
  is 
  rather 
  dolomitic. 
  

   This 
  variety 
  of 
  limestone 
  appears 
  in 
  many 
  excellent 
  exposures, 
  the 
  

   most 
  extensive 
  outcrops 
  perhaps 
  being 
  on 
  the 
  small 
  hill 
  just 
  south 
  

   of 
  Daggett 
  pond. 
  

  

  A 
  second 
  very 
  common 
  variety 
  is 
  nearly 
  white, 
  medium 
  to 
  

   coarse-grained 
  calcitic 
  and 
  with 
  numerous 
  irregular 
  shaped, 
  pel- 
  

   lucid 
  quartz 
  grains, 
  flakes 
  of 
  graphite, 
  and 
  specks 
  of 
  pyrite 
  or 
  

  

  