﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  75 
  

  

  marking 
  the 
  stratification 
  in 
  the 
  beds 
  of 
  the 
  pyroxenite, 
  and 
  in 
  

   one 
  instance, 
  to 
  be 
  described 
  further 
  on, 
  was 
  observed 
  forming 
  a 
  

   small 
  interrupted 
  bed 
  in 
  this 
  rock. 
  The 
  magnetic«ironore, 
  which 
  

   often 
  forms 
  beds 
  in 
  the 
  immediate 
  vicinity 
  of 
  the 
  limestones 
  of 
  the 
  

   Laurentian 
  series, 
  and, 
  like 
  the 
  pyroxenite, 
  is 
  to 
  be 
  regarded 
  as 
  

   belonging 
  to 
  the 
  limestone 
  groups, 
  contains 
  in 
  some 
  places 
  in 
  New 
  

   York, 
  a 
  large 
  admixture 
  of 
  grains 
  or 
  small 
  prisms 
  of 
  apatite, 
  gene- 
  

   ral 
  ly 
  reddish-brown, 
  but 
  sometimes 
  colorless, 
  and 
  occasionally 
  

   associated 
  with 
  grains 
  of 
  green 
  pyroxene. 
  Specimens 
  of 
  a 
  similar 
  

   aggregate 
  of 
  magnetite 
  and 
  apatite 
  are 
  said 
  to 
  have 
  been 
  found 
  on 
  

   the 
  Ottawa; 
  and 
  it 
  is 
  worthy 
  of 
  remark 
  that 
  the 
  extensive 
  beds 
  

   of 
  iron 
  ore 
  found 
  in 
  Laurentian 
  rocks 
  in 
  Grangjarde 
  in 
  Sweden, 
  

   and 
  consisting 
  of 
  an 
  admixture 
  of 
  magnetic 
  and 
  specular 
  oxyds, 
  

   very 
  generally 
  contain 
  grains 
  of 
  apatite, 
  whose 
  presence 
  is 
  sup- 
  

   posed 
  to 
  depreciate 
  the 
  quality 
  of 
  the 
  iron 
  there 
  manufactured. 
  

   (Durocher, 
  Ann. 
  des 
  Mines 
  [4], 
  xv, 
  249). 
  

  

  Serpentine. 
  — 
  This 
  species, 
  though 
  not 
  very 
  common 
  in 
  the 
  

   Laurentian 
  veinstones 
  in 
  Canada, 
  sometimes 
  occurs 
  in 
  small 
  dis- 
  

   seminated 
  grains, 
  or 
  in 
  crystals 
  of 
  considerable 
  size, 
  imbedded 
  in 
  

   calcite. 
  Examples 
  of 
  this 
  occur 
  in 
  North 
  Burgess, 
  where, 
  in 
  one 
  

   locality, 
  imperfectly 
  defined 
  crystals, 
  an 
  inch 
  in 
  diameter, 
  and 
  in 
  

   another, 
  small 
  grains, 
  with 
  corundum, 
  sphene, 
  mica 
  and 
  pyroxene, 
  

   are 
  found; 
  in 
  both 
  cases 
  imbedded 
  in 
  calcite. 
  A 
  massive 
  serpen- 
  

   tine 
  also 
  occurs, 
  forming 
  the 
  gangue 
  of 
  large 
  crystals 
  of 
  mica 
  in 
  

   northern 
  New 
  York. 
  The 
  large 
  crystals 
  of 
  serpentine 
  (sometimes 
  

   enclosing 
  a 
  nucleus 
  of 
  chrysolite) 
  from 
  Snarum 
  in 
  Norway, 
  which, 
  

   according 
  to 
  Scheerer, 
  are 
  accompanied 
  with 
  mica, 
  and 
  imbeded 
  in 
  

   ilmenite, 
  or 
  in 
  magnesite, 
  in 
  the 
  midst 
  of 
  gneiss, 
  probably 
  belong 
  

   to 
  a 
  vein. 
  Crystals 
  resembling 
  them 
  occur 
  in 
  New 
  York 
  [Amer. 
  

   Jour. 
  Science 
  [2J, 
  xvi.) 
  

  

  Distinct 
  from 
  these 
  veins 
  are 
  the 
  small 
  seams 
  filled 
  with 
  fibrous 
  

   serpentine 
  or 
  chrysotile, 
  which 
  are 
  frequently 
  found 
  traversing 
  the 
  

   massive 
  serpentines, 
  or 
  the 
  mixtures 
  of 
  serpentine 
  and 
  limestone 
  

   which 
  make 
  up 
  great 
  beds 
  in 
  the 
  Laurentian 
  series. 
  Massive 
  

   translucent 
  serpentine 
  often 
  occurs 
  as 
  the 
  mineral 
  replacing 
  the 
  

   Eozoon 
  Canadense, 
  the 
  canals 
  of 
  which 
  are 
  in 
  such 
  cases 
  injected 
  

   with 
  this 
  silicate. 
  In 
  some 
  cases 
  the 
  unbroken 
  calcareous 
  skele- 
  

   ton 
  of 
  the 
  fossil 
  is 
  preserved 
  in 
  the 
  serpentine, 
  while 
  in 
  others, 
  

   only 
  broken 
  and 
  detached 
  fragments 
  of 
  the 
  skeleton 
  are 
  found, 
  

   sparsely 
  distributed 
  through 
  the 
  serpentine. 
  The 
  presence 
  of 
  dis- 
  

  

  