﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  83 
  

  

  Small 
  plates 
  of 
  mica, 
  probably 
  a 
  magnesian 
  species, 
  abound 
  

   both 
  in 
  the 
  limestone 
  beds 
  and 
  the 
  pyroxenites, 
  and 
  sometimes 
  

   form 
  layers 
  of 
  a 
  schistose 
  mica-rock, 
  interstratified 
  with 
  the 
  latter. 
  

   Non-magnesian 
  micas, 
  belonging 
  to 
  the 
  species 
  muscovite, 
  mar- 
  

   garodite 
  or 
  lepidolite, 
  are 
  occasionally 
  found 
  in 
  the 
  quartzo-felds- 
  

   pathic 
  veins 
  of 
  the 
  Laurentian 
  series, 
  where 
  compounds 
  of 
  lime 
  

   and 
  magnesia 
  are 
  wanting 
  ; 
  but 
  it 
  is 
  not 
  certain 
  whether 
  they 
  ever 
  

   occur 
  with 
  the 
  calcareous 
  veins 
  or 
  beds. 
  As 
  already 
  remarked, 
  

   the 
  chemical 
  composition 
  of 
  gieseckite, 
  and 
  of 
  the 
  minerals 
  which 
  

   we 
  have 
  provisionally 
  associated 
  with 
  it 
  (wilsonite, 
  algerite 
  and 
  

   dyssyntribite) 
  is 
  identical 
  with 
  the 
  hydrous 
  mica, 
  margarodite, 
  

   which 
  is 
  thus 
  represented 
  in 
  the 
  Laurentian 
  series 
  by 
  these 
  sparry 
  

   silicates, 
  precisely 
  as 
  talc 
  is 
  there 
  represented 
  by 
  pyrallolite 
  

   (Geol 
  Can., 
  pages 
  482-486 
  and 
  492). 
  

  

  Margarite. 
  — 
  This 
  species, 
  the 
  emerylite 
  of 
  Dr. 
  J. 
  Lawrence 
  

   Smith, 
  which 
  may 
  be 
  regarded 
  as 
  a 
  hydrous 
  lime-mica, 
  is 
  men- 
  

   tioned 
  by 
  Blake 
  as 
  occurring 
  with 
  corundum, 
  spinel 
  and 
  calcite 
  in 
  

   a 
  Laurentian 
  veinstone 
  in 
  Vernon, 
  New 
  Jersey, 
  but 
  has 
  not 
  been 
  

   elsewhere 
  identified. 
  

  

  Clintonite. 
  — 
  This 
  mineral, 
  somewhat 
  related 
  in 
  composition 
  to 
  

   the 
  preceding 
  species, 
  occurs 
  in 
  several 
  localities 
  in 
  Orange 
  county, 
  

   New 
  York, 
  with 
  spinel 
  and 
  chondrodite, 
  in 
  calcareous 
  veinstones. 
  

   It 
  has 
  also 
  been 
  observed, 
  with 
  small 
  crystals 
  of 
  blue 
  spinel, 
  in 
  a 
  

   calcareous 
  matrix, 
  in 
  Daillebout, 
  Quebec. 
  

  

  Tourmaline. 
  — 
  This 
  species 
  frequently 
  occurs 
  in 
  the 
  calcareous 
  

   Laurentian 
  veins, 
  with 
  pyroxene, 
  hornblende, 
  apatite 
  and 
  calcite. 
  

   The 
  finest 
  crystals 
  of 
  brown 
  tourmaline 
  in 
  Canada 
  have 
  been 
  found 
  

   in 
  veinstones 
  of 
  flesh-colored 
  calcite, 
  either 
  with 
  or 
  without 
  pale 
  

   green 
  pyroxene, 
  or 
  in 
  a 
  veinstone 
  of 
  translucent 
  quartz. 
  Black 
  

   tourmaline 
  is 
  also 
  occasionally 
  found 
  with 
  pyroxene, 
  but 
  is 
  more 
  

   generally 
  met 
  with 
  in 
  the 
  granitic 
  veinstones, 
  with 
  orthoclase 
  and 
  

   a 
  non-magnesian 
  mica. 
  Tourmaline, 
  in 
  grains 
  or 
  imperfect 
  crystals, 
  

   also 
  occurs 
  in 
  the 
  stratified 
  rocks 
  of 
  the 
  series. 
  In 
  one 
  instance 
  it 
  

   appears 
  in 
  small 
  knot-like 
  masses, 
  in 
  an 
  impure 
  grayish 
  limestone, 
  

   apparently 
  marking 
  the 
  planes 
  of 
  stratification. 
  

  

  Garnet. 
  — 
  This 
  mineral 
  frequently 
  occurs 
  in 
  the 
  veins, 
  some- 
  

   times 
  imbedded 
  in 
  orthoclase 
  or 
  in 
  quartz, 
  at 
  others 
  in 
  calcite, 
  or, 
  

   as 
  at 
  Willsborough, 
  New 
  York, 
  forms 
  granular 
  masses, 
  associated 
  

  

  