﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  77 
  

  

  States, 
  but 
  I 
  have 
  as 
  yet 
  noticed 
  it 
  in 
  Canada 
  only 
  in 
  beds, 
  where 
  

   disseminated 
  grains 
  of 
  chondrodite 
  mark 
  the 
  places 
  of 
  stratifica- 
  

   tion 
  in 
  the 
  limestone. 
  In 
  one 
  instance, 
  in 
  a 
  specimen 
  of 
  limestone 
  

   from 
  an 
  unknown 
  locality, 
  the 
  contact 
  of 
  two 
  la} 
  r 
  ers, 
  one 
  marked 
  

   by 
  grains 
  of 
  chondrodite, 
  and 
  the 
  other 
  by 
  grains 
  of 
  serpentine, 
  is 
  

   distinctly 
  seen. 
  A 
  similar 
  association 
  of 
  the 
  two 
  minerals 
  occurs 
  

   at 
  St. 
  Jerome, 
  in 
  the 
  province 
  of 
  Quebec. 
  

  

  Tephroite, 
  Willemite.— 
  These 
  two 
  rare 
  species, 
  the 
  first 
  a 
  

   silicate 
  of 
  manganese, 
  and 
  the 
  second 
  a 
  silicate 
  of 
  zinc, 
  both 
  of 
  

   them 
  having 
  the 
  general 
  formula 
  of 
  chrysolite, 
  with 
  which 
  the 
  

   former 
  is 
  isomorphotis, 
  have 
  hitherto 
  only 
  been 
  observed 
  in 
  North 
  

   America, 
  in 
  Laurentian 
  veins, 
  crystallized 
  with 
  the 
  frank 
  Unite 
  and 
  

   red 
  zinc 
  ore 
  of 
  Sterling, 
  New 
  Jersey, 
  and 
  its 
  vicinity. 
  

  

  Wollastonite. 
  — 
  This 
  species 
  forms 
  considerable 
  masses 
  in 
  the 
  

   large 
  vein 
  already 
  noticed 
  in 
  Grenville, 
  where 
  its 
  associates 
  in 
  the 
  

   veinstone 
  are 
  pyroxene, 
  orthoclase, 
  quartz, 
  apatite 
  and 
  sphene. 
  In 
  

   smaller 
  specimens 
  it 
  occurs 
  with 
  the 
  same 
  associates 
  in 
  a 
  vein 
  in 
  

   North 
  Elmsley, 
  while 
  in 
  Willsborough, 
  New 
  York, 
  it 
  is 
  found 
  also 
  

   in 
  a 
  vein 
  with 
  grains 
  of 
  green 
  pyroxene, 
  and 
  red 
  granular 
  garnet, 
  

   which 
  latter 
  in 
  some 
  part 
  predominates 
  to 
  the 
  exclusion 
  of 
  the 
  

   other 
  minerals. 
  

  

  As 
  a 
  bed-mineral 
  I 
  have 
  observed 
  it 
  in 
  North 
  Burgess, 
  sparsely 
  

   disseminated 
  in 
  a 
  limestone, 
  with 
  small 
  quantities 
  of 
  green 
  pyrox- 
  

   ene, 
  brown 
  mica 
  and 
  apatite. 
  In 
  the 
  same 
  vicinity, 
  interstratified 
  

   with 
  pyroxenite, 
  are 
  interrupted 
  beds 
  of 
  rock 
  made 
  up 
  of 
  quartz 
  

   and 
  wollastonite. 
  Similar 
  associations 
  to 
  these 
  occur 
  elsewhere 
  

   in 
  the 
  Laurentian 
  strata. 
  

  

  Hornblende. 
  — 
  The 
  hornblende 
  of 
  the 
  Laurentian 
  limestones 
  is 
  

   either 
  in 
  the 
  form 
  of 
  tremolite, 
  or 
  more 
  frequently 
  in 
  green 
  pris- 
  

   matic 
  crystals 
  belonging 
  to 
  the 
  variety 
  called 
  pargasite. 
  The 
  

   raphilite, 
  a 
  grayish 
  fibrous 
  hornblende, 
  allied 
  to 
  tremolite, 
  occurs 
  

   apparently 
  in 
  a 
  vein 
  with 
  quartz, 
  mica, 
  apatite 
  and 
  calcite. 
  Large 
  

   well-defined 
  crystals 
  of 
  dark 
  green 
  pargasite 
  are 
  found 
  implanted 
  

   upon 
  or 
  imbedded 
  in 
  still 
  larger 
  crystals 
  of 
  pale-green 
  pyroxene, 
  

   in 
  a 
  vein 
  described 
  by 
  Sir 
  William 
  Logan 
  as 
  occurring 
  near 
  the 
  

   High 
  Falls 
  on 
  the 
  Madawaska, 
  Ontario, 
  cutting 
  across 
  alternating 
  

   strata 
  of 
  gneiss 
  and 
  limestone, 
  and 
  having 
  a 
  breadth 
  of 
  not 
  less 
  

   than 
  one 
  hundred 
  and 
  fifty 
  feet. 
  The 
  minerals 
  filling 
  this 
  immense 
  

   vein 
  are 
  chiefly 
  a 
  pale 
  grayish-green 
  pyroxene 
  (sahlite), 
  pargasite, 
  

  

  