﻿82 
  Thirtieth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  towards 
  it 
  are 
  embodied 
  in 
  the 
  Canadian 
  Geological 
  Keports. 
  

   Prior 
  to 
  their 
  researches, 
  the 
  rocks 
  underlying 
  the 
  fossiliferons 
  

   strata 
  had 
  not 
  been 
  subdivided 
  into 
  well-characterized 
  groups 
  

   with 
  distinctive 
  local 
  names. 
  The 
  first 
  broadly 
  defined 
  group 
  of 
  

   rocks 
  which 
  were 
  so 
  divided 
  off, 
  were 
  those 
  which 
  are 
  largely 
  

   developed 
  in 
  the 
  rock-masses 
  of 
  the 
  Laurentian 
  Mts., 
  and 
  which 
  

   were 
  accordingly 
  named 
  by 
  the 
  Canadian 
  Survey 
  in 
  1846, 
  the 
  

   Laurentian 
  System. 
  Then, 
  and 
  in 
  subsequent 
  publications 
  of 
  

   the 
  Survey, 
  this 
  name 
  was 
  applied 
  to 
  a 
  vast 
  thickness 
  of 
  highly 
  

   altered 
  metamorphic 
  strata, 
  consisting 
  of 
  feldspathic 
  rocks 
  

   inters 
  tratified 
  with 
  limestones 
  and 
  quartzites. 
  The 
  feldspath- 
  

   ides 
  included 
  both 
  the 
  gneisses, 
  which 
  contained 
  orthoclase 
  and 
  

   other 
  rocks, 
  more 
  or 
  less 
  gneissoid 
  in 
  structure, 
  but 
  composed 
  

   mainly 
  of 
  some 
  variety 
  of 
  triclinic 
  feldspar. 
  The 
  latter 
  were 
  

   further 
  distinguished 
  by 
  a 
  comparative 
  absence 
  of 
  quartz, 
  and 
  

   the 
  association 
  with 
  hypersthene, 
  pyroxene 
  or 
  similar 
  con- 
  

   stituent. 
  At 
  that 
  time 
  they 
  were 
  not 
  put 
  in 
  a 
  separate 
  group, 
  

   but 
  were 
  merely 
  classed 
  together 
  under 
  the 
  general 
  term, 
  

   anorthosites. 
  

  

  The 
  orthoclase 
  gneisses 
  of 
  the 
  Laurentian 
  system 
  are 
  charac- 
  

   terized 
  by 
  their 
  color, 
  which, 
  owing 
  to 
  the 
  potash-feldspar, 
  is 
  

   generally 
  reddish, 
  though 
  sometimes 
  white 
  to 
  bluish 
  -grey, 
  by 
  

   the 
  presence 
  of 
  quartz, 
  and 
  by 
  the 
  frequent 
  occurrence 
  of 
  horn- 
  

   blende 
  and 
  mica. 
  They 
  are 
  both 
  fine- 
  and 
  coarse-grained, 
  in 
  

   the 
  latter 
  case 
  sometimes 
  to 
  such 
  an 
  extent 
  as 
  to 
  present 
  the 
  

   appearance 
  of 
  a 
  granitoid 
  gneiss. 
  The 
  accompanying 
  minerals 
  

   are 
  so 
  disposed 
  about 
  the 
  large 
  cleavable 
  masses 
  of 
  feldspar 
  as 
  

   to 
  give 
  a 
  more 
  or 
  less 
  reticulated 
  appearance 
  to 
  the 
  rock. 
  But, 
  

   in 
  both 
  coarse 
  and 
  fine, 
  the 
  metamorphic 
  character 
  of 
  these 
  

   gneisses, 
  is 
  manifested 
  in 
  the 
  never-failing 
  parallelism 
  of 
  the 
  

   layers, 
  in 
  which 
  the 
  constituent 
  minerals 
  are 
  arranged. 
  These 
  

   two 
  varieties 
  of 
  orthoclase-gneiss, 
  of 
  which 
  the 
  granitoid 
  con- 
  

   stitutes 
  the 
  main 
  peaks 
  and 
  ridges 
  of 
  the 
  orthoclase 
  region 
  and 
  

   is 
  sometimes 
  several 
  thousand 
  feet 
  in 
  thickness, 
  are 
  interstrati- 
  

   fied 
  with 
  bands 
  of 
  limestone 
  and 
  associated 
  with 
  quartzite 
  and 
  

   beds 
  of 
  hornblende 
  and 
  micaceous 
  schist. 
  Masses 
  of 
  pyrox- 
  

   enite 
  are 
  met 
  with 
  near 
  the 
  limestones, 
  and 
  the 
  schists 
  are 
  

   frequently 
  highly 
  garnetiferous. 
  The 
  garnets 
  are 
  sometimes 
  

   disseminated 
  through 
  a 
  pure 
  white 
  orthjoclase, 
  or, 
  associated 
  

   with 
  quartz, 
  characterize 
  many 
  varieties 
  of 
  garnetiferous 
  

  

  