﻿Adams, 
  Barlow 
  and 
  Ells 
  — 
  Canadian 
  Laurentian. 
  175 
  

  

  There 
  can 
  be 
  but 
  little 
  doubt 
  that 
  the 
  various 
  gneissic 
  rocks, 
  

   constituting 
  the 
  more 
  acid 
  part 
  of 
  the 
  series, 
  are 
  of 
  truly 
  

   igneous 
  origin 
  ; 
  and 
  there 
  is 
  no 
  evidence 
  whatever 
  of 
  their 
  

   having 
  ever 
  formed 
  part 
  of 
  a 
  sedimentary 
  series. 
  

  

  The 
  true 
  character 
  of 
  the 
  more 
  basic 
  members 
  is 
  more 
  uncer- 
  

   tain, 
  but 
  they 
  are 
  probably 
  closely 
  related 
  to 
  the 
  pyroxene 
  

   granulites 
  of 
  Saxony, 
  and 
  doubtless 
  represent 
  either 
  differentia- 
  

   tion-products 
  of 
  the 
  original 
  magma, 
  or 
  basic 
  intrusions 
  whose 
  

   structural 
  relations 
  and 
  characters 
  have 
  been 
  largely 
  masked 
  

   by 
  the 
  great 
  movements 
  which 
  have 
  taken 
  place 
  in 
  the 
  whole 
  

   series 
  at 
  a 
  later 
  date. 
  

  

  The 
  Grenville 
  Series 
  differs 
  from 
  the 
  Fundamental 
  Gneiss 
  in 
  

   that 
  it 
  contains 
  certain 
  rocks 
  whose 
  composition 
  marks 
  them 
  as 
  

   highly 
  altered 
  sediments. 
  These 
  rocks 
  are 
  chiefly 
  limestoues, 
  

   with 
  which 
  are 
  associated 
  certain 
  peculiar 
  gneisses, 
  rich 
  in 
  silli- 
  

   manite 
  and 
  garnet, 
  having 
  a 
  composition 
  approaching 
  ordinary 
  

   shale 
  or 
  slate, 
  or 
  else 
  very 
  rich 
  in 
  quartz 
  and 
  passing 
  into 
  

   quartzite, 
  having 
  thus 
  the 
  composition 
  of 
  sandstone. 
  These 
  

   rocks, 
  as 
  has 
  been 
  shown 
  in 
  one 
  of 
  the 
  papers 
  before 
  referred 
  

   to, 
  usually 
  occur 
  in 
  close 
  association 
  with 
  one 
  another, 
  and 
  are 
  

   quite 
  different 
  in 
  composition 
  from 
  any 
  igneous 
  rocks 
  hitherto 
  

   described. 
  They 
  are 
  considered 
  as 
  constituting 
  the 
  essential 
  

   part 
  of 
  the 
  Grenville 
  series. 
  They 
  usually, 
  however, 
  form 
  but 
  

   a 
  very 
  small 
  proportion 
  of 
  the 
  rocky 
  complex 
  in 
  the 
  areas 
  in 
  

   which 
  they 
  occur, 
  and 
  which, 
  owing 
  to 
  their 
  presence, 
  is 
  refer- 
  

   red 
  to 
  the 
  Grenville 
  series. 
  They 
  are 
  associated 
  with 
  and 
  

   often 
  enclosed 
  by 
  much 
  greater 
  volumes 
  of 
  gneissic 
  rocks, 
  

   identical 
  in 
  character 
  with 
  the 
  Fundamental 
  gneiss. 
  The 
  lime- 
  

   stones 
  are 
  also 
  almost 
  invariably 
  penetrated 
  by 
  masses 
  of 
  coarse 
  

   pegmatite, 
  and 
  occasionally 
  large 
  masses 
  of 
  the 
  limestone 
  are 
  

   found 
  embedded 
  in 
  what 
  would 
  otherwise 
  be 
  supposed 
  to 
  be 
  

   the 
  Fundamental 
  gneiss. 
  The 
  whole 
  thus 
  presents 
  a 
  series 
  of 
  sedi- 
  

   mentary 
  rocks, 
  chiefly 
  limestones, 
  invaded 
  by 
  great 
  masses 
  of 
  

   the 
  so-called 
  Fundamental 
  Gneiss, 
  and 
  in 
  which, 
  possibly, 
  some 
  

   varieties 
  of 
  the 
  gneissic 
  rocks 
  present 
  may 
  owe 
  their 
  origin 
  to 
  

   the 
  partial 
  commingling 
  of 
  the 
  sedimentary 
  material 
  with 
  the 
  

   igneous 
  rocks 
  by 
  actual 
  fusion. 
  There 
  is, 
  however, 
  no 
  reason 
  

   to 
  believe, 
  from 
  the 
  evidence 
  at 
  present 
  available, 
  that 
  any 
  

   considerable 
  proportion 
  of 
  the 
  series 
  has 
  originated 
  in 
  the 
  last 
  

   mentioned 
  manner. 
  

  

  It 
  will 
  be 
  readily 
  seen 
  that 
  an 
  exact 
  delimitation 
  of 
  areas 
  of 
  

   the 
  Grenville 
  series 
  is 
  thus 
  sometimes 
  a 
  matter 
  of 
  great 
  diffi- 
  

   culty, 
  as 
  they 
  often 
  appear 
  to 
  shade 
  away 
  into 
  the 
  Fundamental 
  

   gneiss, 
  aud 
  it 
  has 
  hitherto 
  been 
  difficult 
  in 
  the 
  case 
  of 
  the 
  

   Grenville 
  series 
  to 
  account 
  for 
  the 
  existence 
  of 
  such 
  a 
  compar- 
  

   atively 
  small 
  proportion 
  of 
  sedimentary 
  strata, 
  intimately 
  asso- 
  

   ciated 
  with 
  such 
  great 
  volumes 
  of 
  igneous 
  gneisses. 
  

  

  The 
  relations 
  of 
  the 
  two 
  series, 
  as 
  determined 
  by 
  the 
  investi- 
  

   gations 
  of 
  the 
  last 
  two 
  seasons, 
  throws 
  new 
  light 
  upon 
  the 
  sub- 
  

   ject, 
  and 
  indicates 
  the 
  probable 
  explanation 
  of 
  the 
  difficulty. 
  

  

  