﻿484 
  MESSRS. 
  E. 
  I. 
  NEWTON 
  AND 
  J. 
  J. 
  H. 
  TEALL 
  ON 
  [DeC. 
  1 
  89 
  7, 
  

  

  different 
  orientations 
  occur 
  in 
  juxtaposition, 
  so 
  that 
  the 
  ophitic 
  

   structure, 
  though 
  present, 
  is 
  not 
  so 
  marked 
  as 
  it 
  is 
  in 
  many 
  of 
  the 
  

   holocrystallirje 
  dolerites 
  from 
  Iceland, 
  the 
  Eaeroe 
  Islands, 
  and 
  the 
  

   West 
  of 
  Scotland. 
  It 
  resembles 
  in 
  character 
  and 
  mode 
  of 
  occurrence 
  

   the 
  augite 
  of 
  the 
  Tynemouth 
  and 
  related 
  dykes 
  in 
  the 
  North 
  of 
  

   England. 
  1 
  

  

  One 
  rock-specimen, 
  obtained 
  from 
  the 
  underside 
  of 
  an 
  iceberg 
  

   found, 
  tilted 
  up, 
  off 
  Eira 
  Cottage, 
  which 
  otherwise 
  belongs 
  to 
  the 
  

   common 
  type, 
  contains 
  more 
  or 
  less 
  idiomorphic 
  phenocrysts 
  (see 
  

   PI. 
  XXXVII, 
  fig. 
  3) 
  of 
  pale 
  greenish 
  augite, 
  with 
  peripheral 
  inclu- 
  

   sions, 
  in 
  addition 
  to 
  the 
  ordinary 
  augite 
  above 
  described. 
  A 
  few 
  

   grains 
  of 
  this 
  mineral 
  were 
  isolated, 
  and 
  the 
  presence 
  of 
  chromium 
  

   established. 
  It 
  is 
  therefore, 
  as 
  was 
  suspected 
  from 
  its 
  appearance 
  

   under 
  the 
  microscope, 
  a 
  chrome-diopside 
  ; 
  and 
  the 
  fact 
  is 
  of 
  some 
  

   interest 
  from 
  the 
  point 
  of 
  view 
  of 
  correlation, 
  because 
  Scharizer 
  has 
  

   proved 
  the 
  occurrence 
  of 
  this 
  mineral 
  under 
  similar 
  conditions 
  in 
  

   the 
  basalts 
  of 
  Jan 
  May 
  en. 
  2 
  It 
  will 
  be 
  shown 
  subsequently 
  that 
  

   the 
  basalts 
  of 
  Eranz 
  Josef 
  Land 
  have 
  other 
  points 
  of 
  resemblance 
  

   with 
  those 
  of 
  Jan 
  -Mayeu. 
  

  

  The 
  iron-ore 
  occurs 
  as 
  grains, 
  crystalline 
  aggregates, 
  and 
  skeleton- 
  

   crystals. 
  It 
  is 
  strongly 
  magnetic, 
  and 
  is 
  often 
  present 
  in 
  sufficient 
  

   quantity 
  to 
  make 
  the 
  rock 
  magnetic. 
  The 
  felspar 
  and 
  augite 
  are 
  

   as 
  a 
  rule 
  remarkably 
  free 
  from 
  inclusions 
  of 
  this 
  mineral, 
  which 
  

   certainly 
  does 
  not 
  in 
  these 
  rocks 
  belong 
  to 
  the 
  earlier 
  phases 
  of 
  

   consolidation, 
  as 
  it 
  does 
  in 
  so 
  many 
  rocks 
  of 
  intermediate 
  composi- 
  

   tion. 
  In 
  many 
  cases 
  it 
  is 
  found 
  only 
  as 
  skeleton-crystals 
  in 
  the 
  

   interstitial 
  matter 
  (PI. 
  XXXVII, 
  fig. 
  4), 
  and 
  in 
  some 
  the 
  iron- 
  

   oxides 
  have 
  remained 
  wholly 
  undifferentiated 
  in 
  a 
  deep 
  brown 
  glass. 
  

   Olivine 
  is 
  by 
  no 
  means 
  constantly 
  present, 
  and 
  rarely 
  occurs 
  in 
  

   sufficient 
  quantity 
  to 
  give 
  a 
  marked 
  character 
  to 
  the 
  rocks. 
  It 
  

   occurs 
  as 
  grains, 
  and 
  occasionally 
  as 
  more 
  or 
  less 
  idiomorphic 
  

   crystals. 
  When 
  fresh 
  ib 
  is 
  colourless 
  in 
  the 
  thin 
  sections 
  ; 
  but 
  it 
  

   is 
  sometimes 
  represented 
  only 
  by 
  green, 
  or 
  more 
  rarely 
  by 
  brown, 
  

   alteration-products. 
  The 
  occurrence 
  of 
  olivine 
  in 
  sparsely-scattered 
  

   grains 
  or 
  crystals 
  seems 
  to 
  be 
  a 
  special 
  character 
  of 
  this 
  class 
  of 
  

   basalts. 
  Its 
  absence 
  from 
  any 
  particular 
  section 
  does 
  not 
  prove 
  

   that 
  it 
  is 
  entirely 
  absent 
  from 
  the 
  rock, 
  for 
  if 
  several 
  sections 
  be 
  pre- 
  

   pared 
  from 
  one 
  specimen 
  it 
  may 
  be 
  found 
  in 
  some 
  and 
  not 
  in 
  others. 
  

   In 
  addition 
  to 
  the 
  mineralogical 
  constituents 
  above 
  described, 
  

   the 
  rocks 
  invariably 
  contain 
  a 
  certain 
  amount 
  of 
  interstitial 
  matter, 
  

   which 
  assumes 
  different 
  forms 
  in 
  different 
  cases. 
  It 
  may 
  occur 
  as 
  

   a 
  brown 
  glass 
  comparatively 
  free 
  from 
  microlites, 
  as 
  palagonite 
  

   arising 
  from 
  the 
  alteration 
  of 
  this 
  brown 
  glass, 
  or 
  as 
  a 
  fine-grained 
  

   matted 
  aggregate 
  of 
  microlites 
  of 
  augite, 
  magnetite, 
  and 
  felspar, 
  

   with 
  which 
  some 
  colourless 
  base 
  may 
  possibly 
  be 
  associated. 
  

   Transitions 
  from 
  the 
  condition 
  of 
  brown 
  glass 
  to 
  the 
  microlitic 
  type 
  

   may 
  sometimes 
  be 
  observed, 
  and 
  under 
  these 
  circumstances 
  the 
  

   gradual 
  bleaching 
  of 
  the 
  glass 
  by 
  the 
  separation 
  of 
  ferriferous 
  

  

  1 
  ' 
  Petrological 
  Notes 
  on 
  the 
  North-oi-England 
  Dykes.' 
  Quart. 
  Joum. 
  Geol. 
  

   Soc. 
  vol. 
  xl. 
  (1884) 
  p. 
  209- 
  See 
  pi. 
  xii. 
  fig. 
  G. 
  

  

  2 
  ' 
  Ueber 
  Mineralien 
  u. 
  Gesteine 
  vou 
  Jan 
  Mayen,' 
  Jahrb. 
  d. 
  k.-k. 
  gecl. 
  

   Eeichsanst. 
  vol. 
  xxxiv. 
  (1884) 
  p. 
  707. 
  

  

  