﻿84 
  Thirtieth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  Laurentian 
  system,* 
  on 
  the 
  ground 
  of 
  the 
  identity 
  of 
  these 
  

   anorthosites, 
  with 
  a 
  vast 
  extent 
  of, 
  similar 
  rocks 
  found 
  in 
  Nor- 
  

   way, 
  and 
  to 
  which 
  the 
  name 
  of 
  Norite 
  has 
  long 
  since 
  been 
  

   applied 
  by 
  Esmark. 
  

  

  The 
  great 
  value 
  of 
  this 
  creation 
  of 
  the 
  title 
  "Norian 
  System 
  ' 
  : 
  

   is 
  two 
  -fold 
  : 
  — 
  1st, 
  In 
  distinguishing 
  a 
  widely-spread 
  and 
  

   strongly-characterized 
  subdivision 
  of 
  the 
  eozoic 
  rocks, 
  by 
  a 
  

   name 
  applicable 
  to 
  their 
  most 
  important 
  constituent 
  rock, 
  and 
  

   by 
  a 
  local 
  name 
  moreover, 
  which 
  had 
  been 
  previously 
  applied 
  

   to 
  these 
  rocks, 
  from 
  a 
  locality 
  where 
  they 
  had 
  been 
  carefully 
  

   studied. 
  2nd. 
  In 
  fixing 
  the 
  precise 
  meaning 
  of 
  the 
  term 
  Norite, 
  

   and 
  establishing 
  thereby 
  an 
  exact 
  nomenclature 
  for 
  certain 
  

   rocks, 
  which 
  had 
  been 
  very 
  differently 
  classified 
  by 
  preceding 
  

   authors. 
  

  

  The 
  name 
  of 
  Norite 
  was 
  originally 
  applied 
  by 
  Esmark 
  to 
  

   certain 
  Norwegian 
  rocks, 
  which 
  are 
  composed 
  principally 
  of 
  a 
  

   feldspar 
  and 
  hornblende, 
  and 
  which 
  he 
  regarded 
  as 
  a 
  variety 
  

   of 
  diorite. 
  They 
  resembled 
  diorite, 
  moreover, 
  in 
  containing 
  

   quartz 
  and 
  mica. 
  With 
  these 
  diorite-norites, 
  he 
  also 
  included 
  

   some 
  varieties 
  of 
  gabbro.f 
  In 
  this 
  he 
  was 
  followed 
  by 
  Scheerer, 
  

   who 
  called 
  the 
  gabbro 
  of 
  the 
  islands 
  of 
  Anabeloe 
  and 
  Hitteroe, 
  

   norite. 
  It 
  is 
  a 
  mixture 
  of 
  diallage 
  or 
  hypersthene, 
  labradorite, 
  

   soda-orthoclase, 
  and 
  usually 
  some 
  quartz. 
  Both 
  these 
  latter 
  

   minerals 
  are 
  so 
  infrequent 
  in 
  mixture^ 
  of 
  hypersthene 
  and 
  

   labradorite, 
  that 
  such 
  a 
  gabbre 
  would 
  have 
  to 
  be 
  regarded 
  as 
  

   an 
  unusual 
  mineral 
  combination. 
  According 
  to 
  Kjerulf,^: 
  the 
  

   composition 
  of 
  I, 
  a 
  violet 
  norite, 
  consisting 
  of 
  labradorite 
  and 
  

   green 
  diallage, 
  from 
  Tronfjeld, 
  and 
  II, 
  a 
  yellowish-grey 
  norite, 
  

   composed 
  of 
  labradorite, 
  black 
  augite, 
  some 
  tombac-brown 
  

   mica 
  and 
  menaccanite, 
  from 
  Solvsberg, 
  is 
  as 
  follows 
  : 
  

  

  I 
  II 
  

  

  Silica 
  50.06 
  51.47 
  

  

  Alumina 
  16.44 
  15.62 
  

  

  Ferric 
  Oxide 
  7.71 
  12.17 
  

  

  Lime 
  14.66 
  11.69 
  

  

  Magnesia.. 
  4.88 
  4.10 
  

  

  Potash 
  Tr. 
  0.20 
  

  

  Soda 
  1.38 
  0.55 
  

  

  * 
  Amer. 
  Jour. 
  Sci. 
  , 
  1870 
  ( 
  [2] 
  xlix, 
  p. 
  180.) 
  

  

  fZirkel, 
  Lehr. 
  der 
  Petrograpkie, 
  Vol. 
  ii, 
  p. 
  15. 
  

  

  JKjerulf, 
  K 
  Jabrb. 
  f. 
  Min. 
  1863 
  — 
  quoted 
  by 
  Zirkel, 
  ib. 
  p. 
  131. 
  

  

  