﻿488 
  MESSRS. 
  E. 
  T. 
  XEWTOH" 
  A>'D 
  J. 
  J. 
  n. 
  TEALL 
  ON 
  [Dee. 
  1 
  897, 
  

  

  same 
  fact 
  has 
  been 
  established 
  by 
  Yogt 
  in 
  his 
  work 
  on 
  slags. 
  The 
  

   last-mentioned 
  author 
  has 
  made 
  a 
  special 
  study 
  of 
  the 
  conditions 
  

   under 
  which 
  magnetite 
  is 
  formed 
  and 
  has 
  established 
  the 
  fact 
  that 
  

   in 
  basic 
  slags 
  in 
  some 
  cases 
  magnetite 
  precedes 
  olivine, 
  in 
  other 
  cases 
  

   it 
  crystallizes 
  simultaneously 
  with 
  olivine, 
  and 
  in 
  yet 
  others 
  it 
  is 
  

   formed 
  after 
  olivine. 
  1 
  

  

  If 
  we 
  rake 
  the 
  analysis 
  quoted 
  above, 
  minus 
  the 
  water 
  and 
  

   alkali, 
  as 
  representing 
  the 
  composition 
  of 
  the 
  mother-liquor 
  formed 
  

   after 
  the 
  separation 
  of 
  labradorite 
  and 
  augite, 
  it 
  is 
  clear 
  that 
  we 
  

   have 
  still 
  the 
  material 
  necessary 
  to 
  form 
  olivine, 
  magnetite, 
  and 
  

   spinel 
  (hercynite). 
  

  

  In 
  view 
  of 
  the 
  evidence 
  thus 
  furnished 
  of 
  the 
  concentration 
  of 
  

   iron, 
  one 
  is 
  tempted 
  to 
  speculate 
  as 
  to 
  the 
  results 
  that 
  might 
  follow 
  

   if 
  the 
  process 
  were 
  carried 
  still 
  further. 
  Magnetite 
  forms 
  the 
  matrix 
  

   of 
  the 
  cumberlandites 
  of 
  Rhode 
  Island 
  and 
  Taberg, 
  in 
  which 
  olivine 
  

   and 
  felspar 
  occur 
  as 
  phenocrysts. 
  2 
  It 
  is 
  found 
  as 
  interstitial 
  matter 
  

   in 
  the 
  ultrabasic 
  fc 
  schlieren 
  ' 
  in 
  the 
  banded 
  gabbros 
  of 
  Druim 
  an 
  

   Eidhne. 
  3 
  Magnetite 
  and 
  a 
  green 
  spinel 
  (hercynite?) 
  are 
  intimately 
  

   associated 
  in 
  the 
  pyroxenites 
  from 
  Scourie. 
  Metallic 
  iron 
  associated 
  

   with 
  graphite 
  occurs 
  as 
  interstitial 
  matter 
  in 
  certain 
  basalts 
  in 
  

   Greenland. 
  4 
  

  

  Can 
  it 
  be 
  that 
  in 
  some, 
  at 
  least, 
  of 
  these 
  cases 
  we 
  see 
  the 
  extreme 
  

   results 
  of 
  the 
  process 
  indicated 
  above 
  ? 
  

  

  We 
  have 
  now 
  described 
  the 
  principal 
  constituents 
  of 
  the 
  common 
  

   type 
  of 
  basalt. 
  The 
  different 
  specimens 
  vary 
  somewhat 
  as 
  to 
  the 
  

   relative 
  proportions 
  of 
  the 
  several 
  constituents, 
  and 
  still 
  more 
  

   striking 
  differences 
  are 
  due 
  to 
  the 
  presence 
  or 
  absence 
  of 
  amygdaloids. 
  

   The 
  massive 
  varieties 
  are 
  of 
  medium 
  grain, 
  and 
  contain 
  comparatively 
  

   little 
  palagonite 
  or 
  other 
  form 
  of 
  interstitial 
  matter 
  ; 
  the 
  amj-gda- 
  

   loidal 
  varieties 
  are 
  usually 
  of 
  somewhat 
  finer 
  grain, 
  and 
  contain 
  a 
  

   considerable 
  amount 
  of 
  palagonite. 
  The 
  mutual 
  relations 
  of 
  the 
  

   constituents 
  are 
  illustrated 
  in 
  PI. 
  XXXVII, 
  figs. 
  1, 
  2, 
  3, 
  & 
  4. 
  The 
  

   labradorite 
  formed 
  first, 
  and 
  the 
  larger 
  individuals 
  sometimes 
  contain 
  

   glass-inclusions 
  in 
  their 
  central 
  portions. 
  The 
  separation 
  of 
  labra- 
  

   dorite 
  probably 
  left 
  the 
  mother-liquor 
  poorer 
  in 
  alumina, 
  lime, 
  and 
  

   soda, 
  and 
  this 
  facilitated 
  the 
  formation 
  of 
  augite. 
  The 
  common 
  

   augite 
  occurs 
  in 
  irregular 
  grains 
  and 
  patches 
  which 
  are 
  often 
  pene- 
  

   trated 
  by 
  the 
  felspars. 
  The 
  chromc-diopside 
  belongs 
  to 
  an 
  earlier 
  

   phase 
  of 
  consolidation. 
  Magnetite 
  has 
  foi 
  med 
  at 
  different 
  stages, 
  but 
  

   it 
  is 
  commonly 
  associated 
  with 
  the 
  interstitial 
  matter, 
  and 
  in 
  many 
  

   specimens 
  the 
  felspar 
  and 
  augite 
  are 
  almost 
  entirely 
  free 
  from 
  

   inclusions 
  of 
  this 
  mineral. 
  The 
  bulk 
  of 
  the 
  magnetite 
  belongs 
  to 
  a 
  

  

  1 
  ' 
  Beitrage 
  zur 
  Kenntniss 
  der 
  Gesetzeder 
  Mineralbildung 
  in 
  Sehmeizmassen,' 
  

   Archiv 
  for 
  Math, 
  og 
  Naturudensk. 
  Kristiania. 
  

  

  2 
  See 
  ' 
  Lithological 
  Studies,' 
  by 
  M. 
  E. 
  Wadsworth, 
  Mem. 
  Mus. 
  Comp. 
  Zool. 
  

   Harvard, 
  vol. 
  xi. 
  

  

  3 
  ' 
  On 
  the 
  Banded 
  Structure 
  of 
  some 
  Tertiary 
  Gabbros 
  in 
  the 
  Isle 
  of 
  Skye,' 
  

   Geikie 
  &■ 
  Teall, 
  Quart. 
  Journ. 
  Geo 
  1 
  .. 
  Soc. 
  vol. 
  1. 
  ('lS04) 
  p. 
  (545. 
  

  

  4 
  ' 
  On 
  the 
  Existence 
  of 
  Nickel-iron. 
  . 
  . 
  in 
  the 
  Basalt 
  of 
  North 
  Greenland,' 
  

   Tv. 
  J. 
  V. 
  Steenstrup, 
  Min. 
  Mag. 
  vol. 
  vi. 
  (1886) 
  p. 
  1. 
  

  

  