﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NORTH 
  AMERICA. 
  51 
  

  

  It 
  has 
  been 
  pointed 
  out 
  in 
  the 
  Geology 
  of 
  Canada 
  (pages 
  28 
  

   and 
  643), 
  that, 
  in 
  the 
  case 
  of 
  the 
  Laurentian 
  limestones, 
  there 
  is 
  

   abundant 
  evidence 
  that 
  they 
  were 
  at 
  one 
  time 
  in 
  such 
  a 
  plastic 
  con- 
  

   dition 
  that 
  external 
  forces 
  were 
  able, 
  not 
  only 
  to 
  contort 
  great 
  

   masses 
  of 
  limestone, 
  and 
  to 
  break 
  and 
  fold 
  in 
  a 
  remarkable 
  manner 
  

   certain 
  interstratified 
  quartzose 
  layers, 
  but 
  to 
  force 
  the 
  softened 
  

   limestone 
  into 
  fissures 
  in 
  the 
  adjacent 
  silicious 
  strata. 
  Examples 
  

   of 
  the 
  latter 
  phenomenon 
  are, 
  however, 
  comparatively 
  rare, 
  and 
  

   the 
  limestone 
  veins 
  upon 
  which 
  Mr. 
  Emmons, 
  and 
  probably 
  other 
  

   observers, 
  have 
  founded 
  their 
  view 
  of 
  the 
  igneous 
  origin 
  of 
  crys- 
  

   talline 
  limestone, 
  remain 
  to 
  be 
  described, 
  after 
  a 
  brief 
  account 
  of 
  

   the 
  limestones 
  and 
  their 
  immediately 
  associated 
  strata. 
  It 
  should 
  

   here 
  be 
  mentioned 
  that 
  Bischof 
  considers 
  the 
  great 
  dykes 
  of 
  gran- 
  

   ular 
  limestone, 
  which, 
  near 
  Auerbach 
  in 
  the 
  Bergstrasse, 
  are 
  met 
  

   with 
  traversing 
  gneiss, 
  to 
  be 
  deposits 
  from 
  water, 
  filling 
  up 
  fis- 
  

   sures 
  ; 
  in 
  fact, 
  veritable 
  veinstones. 
  (Chem. 
  GeoL, 
  English 
  Ed., 
  iii, 
  

   pp. 
  148-150.) 
  See 
  also 
  the 
  note 
  on 
  page 
  47 
  for 
  a 
  description 
  of 
  

   a 
  similar 
  calcareous 
  vein. 
  

  

  The 
  Laurentian 
  limestones 
  of 
  North 
  America, 
  and 
  other 
  crys- 
  

   talline 
  limestones 
  in 
  different 
  regions, 
  some 
  of 
  which 
  belong 
  to 
  

   other 
  geological 
  periods, 
  often 
  abound, 
  as 
  is 
  well 
  known, 
  in 
  foreign 
  

   minerals. 
  These 
  occur 
  disseminated 
  through 
  the 
  mass 
  of 
  the 
  rock, 
  

   of 
  which 
  they 
  serve, 
  in 
  many 
  cases, 
  to 
  mark 
  the 
  lines 
  of 
  stratifica- 
  

   tion. 
  While 
  some 
  beds 
  consist 
  of 
  nearly 
  pure 
  carbonate 
  of 
  lime, 
  

   others 
  will 
  be 
  found 
  to 
  be 
  characterized 
  by 
  an 
  admixture 
  of 
  grains 
  

   or 
  crystals 
  of 
  chondrocyte, 
  pyroxene, 
  serpentine, 
  mica, 
  feldspar, 
  

   quartz, 
  graphite, 
  or 
  other 
  minerals, 
  either 
  alone 
  or 
  variously 
  asso- 
  

   ciated, 
  and 
  sometimes 
  in 
  such 
  quantities 
  as 
  to 
  make 
  up 
  a 
  large 
  

   proportion 
  of 
  the 
  rock. 
  

  

  Eecent 
  investigations 
  have 
  shown 
  that 
  in 
  some 
  cases 
  the 
  dis- 
  

   semination 
  of 
  certain 
  of 
  these 
  minerals 
  through 
  the 
  crystalline 
  

   limestones 
  is 
  connected 
  with 
  organic 
  forms. 
  The 
  observations 
  of 
  

   Dr. 
  Dawson 
  and 
  myself 
  on 
  the 
  Eozoon 
  Oanadense 
  showed 
  that 
  

   certain 
  silicates, 
  namely, 
  serpentine, 
  pyroxene 
  and 
  loganite, 
  had 
  

   been 
  deposited 
  in 
  the 
  cells 
  and 
  chambers 
  left 
  vacant 
  by 
  the 
  dis- 
  

   appearance 
  of 
  the 
  animal 
  matter 
  from 
  the 
  calcareous 
  skeleton 
  of 
  

   that 
  foraminiferous 
  organism, 
  so 
  that 
  when 
  this 
  calcareous 
  portion 
  

   is 
  removed 
  by 
  an 
  acid 
  there 
  remains 
  a 
  coherent 
  mass, 
  which 
  is 
  a 
  

   cast 
  of 
  the 
  soft 
  parts 
  of 
  the 
  animal, 
  in 
  which 
  not 
  only 
  the 
  cham- 
  

   bers 
  and 
  connecting 
  canals, 
  but 
  the 
  minute 
  tubuli 
  and 
  pores 
  are 
  

   represented 
  by 
  solid 
  mineral 
  silicates. 
  It 
  was 
  shown 
  that 
  this 
  

  

  