﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  55 
  

  

  Laurentian 
  rocks, 
  and 
  have 
  chiefly 
  been 
  studied 
  in 
  connection 
  with 
  

   these 
  limestone 
  groups, 
  where 
  they 
  present 
  the 
  most 
  varied 
  and 
  

   important 
  mineralogical 
  characters. 
  These 
  veins 
  have 
  been 
  briefly 
  

   described 
  in 
  the 
  Geology 
  of 
  Canada, 
  pages 
  35-37, 
  where 
  three 
  

   classes 
  of 
  them 
  are 
  distinguished 
  as 
  follows 
  : 
  

  

  1. 
  Veins 
  filled 
  chiefly 
  with 
  calcareous 
  spar, 
  sometimes 
  with 
  sul- 
  

   phate 
  of 
  barytes 
  or 
  fluor-spar, 
  and 
  carrying 
  sulphuret 
  of 
  lead, 
  and 
  

   more 
  rarely, 
  sulphurets 
  of 
  zinc, 
  iron 
  and 
  copper. 
  Numbers 
  of 
  

   these 
  metalliferous 
  veins 
  have 
  been 
  described 
  in 
  speaking 
  of 
  the 
  

   various 
  metals 
  in 
  chapter 
  xxi 
  of 
  the 
  Geology, 
  and 
  others 
  are 
  

   noticed 
  by 
  Mr. 
  Macfarlane 
  in 
  his 
  report 
  on 
  the 
  county 
  of 
  Hastings 
  

   (Geol. 
  Survey 
  of 
  Canada, 
  1866). 
  These 
  veins 
  are 
  much 
  newer 
  

   than 
  the 
  Laurentian 
  rocks, 
  since 
  they 
  traverse 
  in 
  Ramsay, 
  Ontario, 
  

   the 
  strata 
  of 
  the 
  Calciferous 
  formation 
  (Geol. 
  Can., 
  page 
  636). 
  

   Similar 
  veins 
  are 
  also 
  met 
  with 
  in 
  Lewis 
  county, 
  New 
  York, 
  inter- 
  

   secting 
  the 
  limestones 
  of 
  the 
  Trenton 
  group, 
  and 
  sometimes 
  

   containing 
  fluor-spar. 
  The 
  vein 
  in 
  the 
  Laurentian 
  limestone 
  on 
  

   Muscalunge 
  lake, 
  St. 
  Lawrence 
  county, 
  New 
  York, 
  which 
  contains 
  

   besides 
  calcite, 
  the 
  huge 
  crystals 
  of 
  fluor-spar 
  so 
  well 
  known 
  to 
  

   mineralogists, 
  may 
  probably 
  belong 
  to 
  the 
  same 
  class 
  as 
  the 
  lead- 
  

   bearing 
  veins 
  just 
  mentioned.* 
  

  

  2. 
  The 
  veins 
  of 
  the 
  second 
  class 
  are 
  filled 
  with 
  quartz 
  and 
  

   orthoclase 
  feldspar, 
  which 
  is 
  sometimes 
  replaced 
  by, 
  or 
  associated 
  

   with 
  albite. 
  These 
  veins 
  occasionally 
  include 
  crystals 
  of 
  black 
  or 
  

   white 
  mica 
  (muscovite), 
  large 
  crystals 
  of 
  black 
  hornblende, 
  and 
  

   not 
  unfrequently 
  black 
  tourmaline, 
  red 
  garnet 
  and 
  zircon. 
  One 
  

   of 
  this 
  class, 
  cutting 
  the 
  Laurentian 
  gueiss 
  in 
  Greenfield, 
  near 
  

   Saratoga, 
  New 
  York, 
  contains, 
  in 
  addition 
  to 
  garnet 
  and 
  tourma- 
  

   line, 
  the 
  rare 
  species 
  chrysoberyl 
  ; 
  and. 
  the 
  granitic 
  vein 
  holding 
  

   crystals 
  of 
  beryl, 
  observed 
  by 
  Dr. 
  Bigsby 
  in 
  the 
  gneiss 
  of 
  Rainy 
  

  

  * 
  In 
  this 
  connection 
  may 
  be 
  mentioned 
  a 
  vein 
  of 
  this 
  class, 
  remarkable 
  for 
  its 
  size, 
  which 
  

   occurs 
  at 
  Spencerville, 
  near 
  Prescott, 
  Ontario, 
  and 
  has 
  attracted 
  some 
  attention 
  in 
  the 
  

   neighborhood. 
  It 
  is 
  on 
  the 
  east 
  half 
  of 
  lot 
  twenty-eight, 
  in 
  the 
  sixth 
  range 
  of 
  Edwards- 
  

   burg, 
  and 
  cuts 
  the 
  horizontal 
  strata 
  of 
  the 
  Calciferous 
  formation, 
  which 
  is 
  here 
  bare 
  of 
  

   soil, 
  and 
  holds 
  nodules 
  of 
  chert. 
  The 
  vein, 
  which 
  runs 
  E. 
  N. 
  E., 
  has 
  been 
  traced 
  on 
  the 
  

   surface 
  for 
  a 
  distance 
  of 
  about 
  one 
  hundred 
  rods, 
  and 
  at 
  the 
  place 
  where 
  it 
  has 
  been 
  

   opened 
  is 
  not 
  less 
  than 
  eighteen 
  feet 
  wide, 
  and 
  vertical 
  in 
  its 
  attitude. 
  A 
  pit 
  had 
  been 
  

   sunk 
  on 
  the 
  vein 
  at 
  the 
  time 
  of 
  my 
  visit, 
  in 
  August, 
  1864, 
  to 
  depth 
  of 
  twenty 
  feet. 
  The 
  

   veinstone 
  was 
  pure 
  white 
  crystalline 
  carbonate 
  of 
  lime, 
  without 
  any 
  traces 
  of 
  banded 
  struc- 
  

   ture 
  ; 
  and 
  in 
  detached 
  blocks 
  the 
  greater 
  part 
  of 
  it 
  could 
  not 
  be 
  distinguished 
  from 
  many 
  

   saccharoidal 
  limestones. 
  Occasionally, 
  however, 
  masses 
  of 
  a 
  coarsely 
  eleavable 
  and 
  lilac- 
  

   colored 
  calcite 
  were 
  met 
  with. 
  The 
  only 
  foreign 
  minerals 
  in 
  this 
  vein 
  were 
  small 
  and 
  rare 
  

   grains 
  of 
  copper 
  pyrites, 
  and 
  more 
  frequently, 
  iron 
  pyrites 
  in 
  thin 
  testaceous 
  crusts, 
  also 
  

   very 
  sparsely 
  distributed. 
  Another, 
  and 
  a 
  smaller 
  vein, 
  was 
  observed 
  nearly 
  parallel 
  to 
  

   this, 
  filled 
  with 
  a 
  similar 
  carbonate 
  of 
  lime, 
  but 
  without 
  any 
  visible 
  metallic 
  impregnation. 
  

  

  