﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  73 
  

  

  Heavy-Spar. 
  — 
  The 
  heavy-spar 
  found 
  in 
  the 
  Laurentian 
  rocks, 
  

   generally 
  belongs 
  to 
  the 
  recent 
  or 
  lead-bearing 
  veins, 
  but 
  some- 
  

   times 
  appears 
  in 
  the 
  older 
  veins. 
  In 
  addition 
  to 
  that 
  just 
  mentioned 
  

   as 
  occurring 
  at 
  Iron 
  Island, 
  small 
  quantities 
  of 
  flesh-red 
  lamellar 
  

   sulphate 
  of 
  barytes 
  are 
  found 
  with 
  quartz, 
  implanted 
  on 
  apatite, 
  

   in 
  a 
  vein 
  in 
  Burgess. 
  

  

  Apatite. 
  — 
  This 
  is 
  one 
  of 
  the 
  most 
  abundant 
  minerals 
  in 
  the 
  

   Laurentian 
  veinstones, 
  of 
  which 
  it 
  sometimes 
  constitutes 
  the 
  entire 
  

   mass, 
  appearing, 
  as 
  described 
  on 
  page 
  761 
  of 
  the 
  Geology, 
  as 
  a 
  

   crystalline, 
  homogeneous 
  rock, 
  translucent, 
  with 
  an 
  uneven 
  frac- 
  

   ture, 
  a 
  vitreous 
  lustre, 
  and 
  a 
  grayish 
  color, 
  passing 
  into 
  greenish 
  

   or 
  reddish. 
  It 
  then 
  resembles 
  in 
  its 
  aspect 
  some 
  varieties 
  of 
  

   quartzite, 
  and 
  at 
  other 
  times 
  consists 
  of 
  incoherent 
  grains, 
  resem- 
  

   bling 
  a 
  disintegrating 
  sandstone. 
  Another 
  variety 
  is 
  more 
  coarsely 
  

   crystalline, 
  sea-green 
  in 
  color, 
  and, 
  like 
  the 
  last, 
  intermixed 
  with 
  

   a 
  little 
  black 
  mica. 
  In 
  this 
  instance, 
  large 
  and 
  distinct 
  prisms 
  of 
  

   apatite, 
  with 
  rounded 
  angles, 
  are 
  observed 
  penetrating 
  the 
  con- 
  

   fusedly 
  crystalline 
  mass 
  of 
  the 
  same 
  mineral, 
  which 
  has 
  apparently 
  

   been 
  deposited 
  upon 
  and 
  around 
  them. 
  The 
  locality 
  of 
  this 
  variety 
  

   is 
  on 
  the 
  twenty-fifth 
  lot 
  of 
  the 
  eighth 
  range 
  of 
  North 
  Elmsley, 
  

   Ontario 
  (which 
  is 
  described 
  in 
  the 
  Geology 
  as 
  a 
  bed, 
  but 
  is 
  proba- 
  

   bly 
  a 
  vein). 
  There, 
  adjoining 
  three 
  feet 
  of 
  nearly 
  pure 
  apatite, 
  

   is 
  found 
  an 
  admixture 
  of 
  crystals 
  of 
  apatite 
  with 
  crystalline 
  flesh- 
  

   colored 
  carbonate 
  of 
  lime, 
  accompanied 
  by 
  loganite 
  and 
  sphene. 
  

   In 
  several 
  other 
  localities 
  in 
  this 
  region, 
  outcrops 
  of 
  a 
  precisely 
  

   similar 
  aggregate 
  are 
  found, 
  which 
  would 
  be 
  described 
  as 
  crystal- 
  

   line 
  limestones, 
  generally 
  reddish 
  or 
  pink 
  in 
  color, 
  and 
  including 
  

   crystals 
  and 
  irregular 
  crystalline 
  masses 
  of 
  green 
  apatite, 
  sometimes 
  

   associated 
  with 
  large 
  prisms 
  of 
  magnesian 
  mica. 
  In 
  those 
  places 
  

   where 
  it 
  has 
  been 
  possible 
  to 
  determine 
  the 
  attitude 
  of 
  these 
  

   aggregates, 
  it 
  is 
  very 
  evident 
  that 
  they 
  are 
  true 
  veinstones, 
  cutting 
  

   the 
  bedded 
  rocks 
  of 
  the 
  country. 
  Crystals 
  of 
  apatite 
  several 
  inches 
  

   in 
  diameter 
  are 
  often 
  met 
  with, 
  and 
  one 
  in 
  the 
  Museum 
  of 
  the 
  

   Geological 
  Survey 
  is 
  eighteen 
  inches 
  long 
  and 
  twenty-six 
  inches 
  

   in 
  circumference, 
  and 
  weighs 
  about 
  one 
  hundred 
  pounds. 
  Like 
  

   all 
  the 
  apatite 
  crystals 
  from 
  this 
  region, 
  its 
  lateral 
  and 
  terminal 
  

   angles 
  are 
  very 
  much 
  rounded. 
  The 
  apatite 
  crystals 
  of 
  these 
  

   veinstones 
  are 
  generally 
  of 
  some 
  shade 
  of 
  green 
  ; 
  but 
  in 
  Ross, 
  

   crystals 
  of 
  a 
  reddish-brown 
  color 
  are 
  met 
  with, 
  and 
  others 
  of 
  an 
  

  

  