﻿LAURENTTAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  87 
  

  

  botli 
  of 
  North 
  America 
  and 
  of 
  Scandinavia, 
  has 
  been 
  shown 
  by 
  the 
  

   explorations 
  of 
  the 
  Geological 
  survey 
  in 
  Canada 
  to 
  occur 
  in 
  great 
  

   beds, 
  interstratified 
  with 
  the 
  limestones 
  of 
  the 
  series 
  or 
  in 
  their 
  

   vicinity. 
  This 
  is 
  clearly 
  the 
  case 
  with 
  all 
  the 
  considerable 
  de- 
  

   posits 
  of 
  ore 
  hitherto 
  examined 
  in 
  Canada 
  ; 
  yet, 
  as 
  in 
  the 
  case 
  of 
  

   the 
  crystalline 
  limestones, 
  there 
  are 
  those 
  who 
  .maintain 
  the 
  erup- 
  

   tive 
  character 
  and 
  igneous 
  origin 
  of 
  these 
  masses 
  of 
  ore. 
  Emmons 
  

   looked 
  upon 
  the 
  magnetic 
  iron 
  ores 
  of 
  northern 
  New 
  York 
  as 
  

   intrusive 
  masses, 
  and 
  Prof. 
  H, 
  D. 
  Rogers 
  in 
  like 
  manner 
  regarded 
  

   the 
  magnetic 
  iron 
  ores 
  of 
  the 
  Laurentian 
  strata 
  of 
  New 
  Jersey 
  not 
  as 
  

   beds, 
  but 
  as 
  real 
  veins 
  of 
  injection 
  {Final 
  Report, 
  Geol. 
  JV. 
  Jersey, 
  

   page 
  22). 
  Durocher 
  in 
  like 
  manner, 
  in 
  describing 
  the 
  deposit 
  of 
  

   the 
  same 
  ore 
  at 
  Bispberg 
  in 
  Sweden, 
  speaks 
  of 
  it 
  as 
  a 
  " 
  plutonic 
  

   rock' 
  7 
  injected 
  among 
  the 
  beds 
  of 
  gneiss 
  in 
  the 
  plane 
  of 
  stratifica- 
  

   tion, 
  and 
  having 
  a 
  thickness 
  of 
  from 
  eighty 
  to 
  one 
  hundred 
  feet. 
  

   He 
  elsewhere 
  speaks 
  of 
  the 
  injection 
  of 
  the 
  masses 
  of 
  a 
  similar 
  

   ore 
  near 
  Arendal 
  (Ann. 
  des 
  Mines, 
  [4], 
  xv, 
  pp. 
  203, 
  204, 
  225). 
  

   A 
  careful 
  study 
  of 
  his 
  descriptions 
  and 
  plans 
  will, 
  however, 
  we 
  

   think, 
  show 
  that 
  these 
  great 
  deposits 
  of 
  Scandinavia 
  are, 
  like 
  the 
  

   similar 
  masses 
  of 
  ore 
  in 
  Canada 
  and 
  the 
  United 
  States, 
  interstrati- 
  

   fied 
  sedimentary 
  layers. 
  At 
  the 
  same 
  time 
  there 
  exists 
  in 
  favor 
  

   of 
  the 
  view 
  maintained 
  by 
  Emmons, 
  Rogers, 
  Durocher, 
  and 
  other 
  

   geologists, 
  evidence 
  similar 
  to 
  that 
  adduced 
  in 
  favor 
  of 
  the 
  erup- 
  

   tive 
  origin 
  of 
  crystalline 
  limestones 
  ; 
  that 
  is 
  to 
  say, 
  the 
  fact 
  of 
  

   veinstones 
  consisting 
  wholly 
  or 
  in 
  part 
  of 
  magnetic 
  oxyd 
  of 
  iron, 
  

   An 
  interesting 
  example 
  of 
  this 
  occurs 
  near 
  Dover, 
  New 
  Jersey, 
  

   where 
  large 
  crystals 
  of 
  apatite 
  occur 
  in 
  a 
  gangue 
  composed 
  of 
  tri- 
  

   clinic 
  feldspar 
  and 
  iron 
  pyrites, 
  imbedded 
  in 
  which 
  latter 
  occurs 
  

   crystalline 
  magnetite 
  in 
  rounded 
  masses, 
  sometimes 
  half 
  an 
  inch 
  

   in 
  diameter, 
  that 
  were 
  at 
  first 
  taken 
  for 
  ilmenite. 
  Similar 
  associ- 
  

   ations 
  have 
  been 
  observed 
  in 
  other 
  veins, 
  and 
  it 
  is 
  not 
  improbable 
  

   that 
  the 
  mixture 
  of 
  magnetite 
  with 
  a 
  large 
  proportion 
  of 
  zircon, 
  

   described 
  under 
  the 
  head 
  of 
  this 
  species, 
  may 
  be 
  from 
  a 
  veinstone. 
  

   Another 
  and 
  an 
  instructive 
  instance 
  is 
  that 
  described 
  by 
  Sir 
  Wil- 
  

   liam 
  Logan 
  as 
  occurring 
  in 
  the 
  township 
  of 
  Ross, 
  opposite 
  Portage 
  

   du 
  Fort. 
  Here 
  a 
  vein, 
  or 
  rather 
  a 
  group 
  of 
  reticulating 
  veins 
  and 
  

   cracks, 
  is 
  seen 
  in 
  a 
  white 
  granular 
  Laurentian 
  limestone, 
  cutting 
  

   across 
  the 
  stratification, 
  and 
  sending 
  off 
  branches 
  on 
  either 
  side 
  in 
  

   the 
  plane 
  of 
  the 
  limestone 
  beds. 
  These 
  veins 
  vary 
  from 
  a 
  six- 
  

   teenth 
  of 
  an 
  inch 
  to 
  two 
  or 
  three 
  inches 
  in 
  thickness, 
  and 
  are 
  

   filled 
  with 
  highly 
  crystalline 
  magnetite, 
  which 
  in 
  contact 
  with 
  the 
  

  

  