﻿LAURENTIAN 
  LIMESTONES 
  OF 
  NOETH 
  AMERICA. 
  49 
  

  

  not 
  less 
  than 
  18,000 
  feet, 
  where 
  it 
  lies 
  between 
  the 
  Laurentian 
  and 
  

   Silurian 
  systems, 
  conformable 
  with 
  neither. 
  It 
  is 
  believed 
  to 
  be 
  

   newer 
  than 
  the 
  Labrador 
  series, 
  though 
  the 
  two 
  have 
  never 
  yet 
  

   been 
  seen 
  in 
  contact. 
  The 
  recent 
  observations 
  of 
  Prof. 
  Hall, 
  have 
  

   shown 
  that 
  the 
  Huronian 
  system 
  is 
  found 
  interposed 
  between 
  the 
  

   Silurian 
  and 
  the 
  Laurentian 
  to 
  the 
  west 
  of 
  the 
  Mississippi, 
  while 
  

   it 
  appears 
  to 
  have 
  been 
  very 
  recently 
  identified 
  both 
  in 
  New- 
  

   foundland 
  and 
  in 
  New 
  Brunswick. 
  Of 
  these 
  three 
  great 
  series, 
  

   Sir 
  William 
  Logan 
  remarks 
  that 
  their 
  united 
  thickness 
  "may 
  pos- 
  

   sibly 
  far 
  surpass 
  that 
  of 
  all 
  the 
  succeeding 
  rocks 
  from 
  the 
  base 
  of 
  

   the 
  Potsdam 
  series 
  to 
  the 
  present 
  time. 
  We 
  are 
  thus 
  carried 
  back 
  

   to 
  a 
  period 
  so 
  far 
  remote, 
  that 
  the 
  appearance 
  of 
  the 
  so-called 
  pri- 
  

   mordial 
  fauna 
  may 
  by 
  some 
  be 
  considered 
  a 
  comparatively 
  modern 
  

   event. 
  We 
  find, 
  however, 
  that 
  even 
  during 
  the 
  Laurentian 
  period, 
  

   the 
  same 
  chemical 
  and 
  mechanical 
  processes 
  which 
  have 
  ever 
  since 
  

   been 
  at 
  work 
  disintegrating 
  and 
  reconstructing 
  the 
  earth's 
  crust, 
  

   were 
  in 
  operation, 
  as 
  now. 
  In 
  the 
  conglomerates 
  of 
  the 
  Huronian 
  

   series, 
  there 
  are 
  enclosed 
  boulders 
  derived 
  from 
  the 
  Laurentian, 
  

   that 
  seem 
  to 
  show 
  that 
  the 
  parent 
  rock 
  was 
  altered 
  to 
  its 
  present 
  

   crystalline 
  condition 
  before 
  the 
  deposit 
  of 
  the 
  newer 
  .formation, 
  

   while 
  interstratiiied 
  with 
  the 
  Laurentian 
  limestones, 
  there 
  are 
  

   beds 
  of 
  conglomerate, 
  the 
  pebbles 
  of 
  which 
  are 
  themselves 
  rolled 
  

   fragments 
  of 
  a 
  still 
  older 
  laminated 
  sand-rock 
  ; 
  and 
  the 
  forma- 
  

   tion 
  of 
  these 
  beds 
  leads 
  us 
  still 
  further 
  into 
  the 
  past." 
  [Quar. 
  Jow\ 
  

   Geol 
  Soc, 
  February, 
  1865.) 
  

  

  The 
  area 
  occupied 
  by 
  the 
  Laurentian 
  rocks 
  in 
  Canada, 
  is 
  about 
  

   200,000 
  square 
  miles, 
  of 
  which 
  about 
  1,500 
  square 
  miles 
  have 
  

   been 
  accurately 
  studied 
  and 
  mapped 
  in 
  the 
  valley 
  of 
  the 
  Ottawa, 
  

   in 
  the 
  province 
  of 
  Quebec, 
  and 
  a 
  still 
  smaller 
  area 
  in 
  the 
  county 
  

   of 
  Hastings, 
  Ontario. 
  The 
  Laurentian 
  area 
  of 
  the 
  Adirondacks, 
  

   in 
  northern 
  New 
  York, 
  comprises 
  about 
  10,000 
  square 
  miles, 
  but 
  

   has 
  never 
  yet 
  been 
  stratigraphically 
  studied, 
  although 
  much 
  atten- 
  

   tion 
  has 
  been 
  paid 
  to 
  the 
  mineralogy 
  of 
  the 
  limestones 
  of 
  the 
  series, 
  

   which 
  present 
  many 
  characters 
  both 
  of 
  scientific 
  and 
  of 
  economic 
  

   interest. 
  The 
  following 
  pages 
  are 
  extracted 
  from 
  the 
  Eeport 
  of 
  

   the 
  Geological 
  Survey 
  of 
  Canada 
  for 
  1863-66 
  (pages 
  182-223), 
  

   published 
  at 
  Ottawa, 
  and 
  here 
  reprinted 
  with 
  some 
  few 
  additions, 
  

   which 
  are 
  distinguished 
  by 
  being 
  enclosed 
  in 
  brackets 
  : 
  

  

  The 
  evidence 
  afforded 
  by 
  the 
  careful 
  stratigraphical 
  study 
  of 
  

   these 
  Laurentian 
  limestones, 
  and 
  their 
  associated 
  rocks 
  in 
  the 
  vaL 
  

  

  