﻿30 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  and 
  white 
  rock 
  which 
  is 
  of 
  common 
  occurrence 
  in 
  the 
  Grenville 
  

   wherever 
  known. 
  In 
  the 
  writer's 
  experience 
  this 
  is 
  far 
  from 
  being 
  

   true 
  of 
  the 
  quartzose 
  limestone 
  which 
  occurs 
  in 
  much 
  greater 
  force 
  

   here 
  than 
  is 
  customary. 
  

  

  Of 
  the 
  various 
  Grenville 
  rocks 
  the 
  limestones 
  are 
  much 
  more 
  

   yielding 
  under 
  compressive 
  stresses 
  than 
  are 
  the 
  schists 
  and 
  quart- 
  

   zites, 
  behave 
  more 
  like 
  plastic 
  and 
  less 
  like 
  brittle 
  bodies, 
  and 
  hence 
  

   change 
  shape 
  more 
  readily. 
  As 
  a 
  result 
  rocks 
  which 
  much 
  resemble 
  

   coarse 
  conglomerates 
  are 
  a 
  frequent 
  feature 
  in 
  the 
  Grenville 
  lime- 
  

   stone. 
  Frequent 
  dikes 
  of 
  granite 
  traverse 
  it, 
  many 
  of 
  which 
  are 
  of 
  

   slender 
  width. 
  Under 
  compression 
  these 
  are 
  brittle 
  under 
  condi- 
  

   tions 
  which 
  are 
  sufficient 
  to 
  cause 
  flowage 
  in 
  the 
  limestone, 
  hence 
  

   the 
  dikes 
  fracture^ 
  the 
  separate 
  fragments 
  are 
  somewhat 
  shifted 
  in 
  

   position 
  and 
  limestone 
  is 
  squeezed 
  in 
  between 
  them. 
  The 
  same 
  

   thing 
  takes 
  place 
  where 
  thin 
  bands 
  of 
  quartzite 
  or 
  of 
  schist 
  are 
  

   present 
  in 
  the 
  limestone, 
  as 
  is 
  frequently 
  the 
  case. 
  These 
  frag- 
  

   ments 
  of 
  granite, 
  quartzite 
  or 
  schist 
  weather 
  less 
  rapidly 
  than 
  the 
  

   surrounding 
  limestone, 
  and 
  hence 
  project 
  somewhat 
  on 
  weathered 
  

   surfaces, 
  with 
  considerable 
  increase 
  in 
  conspicuousness, 
  and 
  the 
  

   separate 
  fragments 
  surrounded 
  by 
  calcite 
  give 
  an 
  admirable 
  mim- 
  

   icry 
  of 
  a 
  conglomerate 
  in 
  appearance. 
  

  

  In 
  addition 
  to 
  the 
  normal 
  white 
  limestone 
  frequent 
  patches 
  or 
  

   streaks 
  of 
  gray 
  or 
  blue 
  limestone 
  also 
  occur 
  in 
  association 
  with 
  it, 
  

   which 
  outwardly 
  look 
  much 
  more 
  like 
  ordinary 
  limestone. 
  This 
  

   is 
  in 
  line 
  with 
  the 
  further 
  fact 
  that 
  all 
  the 
  Grenville 
  rocks 
  seem 
  

   somewhat 
  less 
  severely 
  metamorphosed 
  than 
  is 
  the 
  case 
  with 
  the 
  

   equivalent 
  rocks 
  to 
  the 
  eastward. 
  Even 
  the 
  white 
  marble 
  has 
  at 
  

   times 
  a 
  grayish 
  or 
  bluish 
  cast, 
  and 
  does 
  not 
  average 
  as 
  coarsely 
  

   crystalline 
  as 
  the 
  eastern 
  Grenville 
  limestone. 
  On 
  the 
  other 
  hand 
  

   limestone 
  of 
  these 
  characters 
  is 
  commonly 
  not 
  so 
  pure 
  as 
  is 
  much 
  

   of 
  the 
  white 
  limestone, 
  and 
  these 
  gray 
  or 
  blue 
  portions 
  often 
  occur 
  

   in 
  such 
  situation 
  as 
  to 
  suggest 
  that 
  they 
  are 
  contact 
  effects 
  of 
  

   igneous 
  rocks 
  on 
  the 
  white 
  limestone. 
  In 
  some 
  instances 
  certainly 
  

   the 
  white 
  limestone 
  changes 
  to 
  gray 
  adjacent 
  to 
  an 
  igneous 
  rock 
  

   mass 
  of 
  good 
  size, 
  and 
  in 
  others 
  gray 
  patches 
  in 
  white 
  limestone 
  

   occur 
  in 
  direct 
  contact 
  with 
  granite 
  dikes, 
  an 
  unlikely 
  situation 
  if 
  

   they 
  are 
  really 
  less 
  metamorphosed 
  portions 
  of 
  the 
  white 
  limestone. 
  

   It 
  is 
  also 
  true, 
  however, 
  that 
  some 
  of 
  the 
  gray 
  limestone 
  is 
  very 
  

   pure, 
  that 
  in 
  some 
  places 
  it 
  has 
  no 
  discoverable 
  nearness 
  to 
  any 
  

   igneous 
  rock, 
  and 
  that 
  in 
  general 
  the 
  contact 
  action 
  of 
  the 
  igneous 
  

   rocks 
  of 
  the 
  district 
  upon 
  the 
  limestone 
  has 
  been 
  but 
  slight, 
  though 
  

   with 
  local 
  exceptions 
  to 
  this 
  statement. 
  With 
  such 
  arguments 
  in 
  

  

  