﻿Vol. 
  53.] 
  ROCKS 
  AXD 
  FOSSILS 
  FROM 
  FRANZ 
  JOSEF 
  LAND. 
  487 
  

  

  of 
  about 
  2'9. 
  The 
  palagonito 
  has 
  arisen 
  from 
  the 
  hydration 
  of 
  

   the 
  glass 
  formed 
  by 
  the 
  consolidation 
  of 
  the 
  mother-liquor 
  out 
  

   oi* 
  which 
  the 
  other 
  constituents, 
  mainly 
  labradorite 
  and 
  augite, 
  

   have 
  crystallized. 
  If 
  we 
  assume 
  that 
  the 
  only 
  chemical 
  change 
  

   which 
  has 
  taken 
  place 
  is 
  that 
  of 
  hydration, 
  then 
  the 
  percentage 
  

   composition 
  of 
  the 
  mother-liquor 
  would 
  be 
  as 
  follows 
  : 
  — 
  

  

  SiO., 
  42-88 
  

  

  A1 
  3 
  0, 
  1003 
  

  

  Fe 
  9 
  3 
  14-86 
  

  

  FeO 
  17-65 
  

  

  CaO 
  1-2G 
  

  

  MgO 
  8-58 
  

  

  Na^O 
  474 
  

  

  100-00 
  

  

  In 
  view 
  of 
  the 
  researches 
  of 
  Lemberg 
  * 
  and 
  the 
  observations 
  

   of 
  Murray 
  & 
  lienard 
  the 
  above 
  assumption 
  is 
  not 
  warranted. 
  

   Alkalies 
  may 
  have 
  been 
  added, 
  and 
  lime 
  and 
  magnesia 
  removed. 
  

   There 
  is, 
  however, 
  no 
  reason 
  to 
  believe 
  that 
  the 
  relative 
  amounts 
  of 
  

   alumina 
  and 
  iron 
  have 
  been 
  appreciably 
  changed, 
  and 
  we 
  are 
  

   therefore 
  able 
  to 
  draw 
  the 
  important 
  conclusion 
  that 
  in 
  a 
  magma 
  of 
  

   the 
  type 
  to 
  which 
  these 
  basalts 
  belong 
  — 
  that 
  is, 
  a 
  basic 
  magma 
  poor 
  

   iu 
  alkalies 
  — 
  progressive 
  crystallization 
  leads 
  to 
  the 
  formation 
  of 
  

   a 
  mother-liquor 
  poor 
  in 
  silica 
  and 
  alumina 
  and 
  rich 
  in 
  iron. 
  It 
  

   is 
  possible 
  that 
  the 
  relative 
  amounts 
  of 
  lime 
  and 
  magnesia 
  have 
  not 
  

   been 
  seriously 
  modified 
  by 
  the 
  hydration, 
  and 
  if 
  to 
  we 
  see 
  that 
  

   crystallization 
  niay, 
  at 
  any 
  rate 
  in 
  its 
  earlier 
  stages, 
  tend 
  to 
  increase 
  

   the 
  relative 
  amount 
  of 
  magnesia. 
  The 
  partial 
  separation 
  of 
  the 
  

   lime, 
  alumina, 
  and 
  silica 
  from 
  the 
  iron 
  and 
  magnesia 
  is 
  of 
  course 
  

   effected 
  by 
  the 
  crystallization 
  of 
  basic 
  felspars, 
  which 
  in 
  this 
  class 
  of 
  

   rocks 
  precede 
  the 
  augites 
  and 
  sometimes 
  even 
  the 
  olivine.'' 
  

  

  This 
  concentration 
  of 
  the 
  iron, 
  and 
  to 
  a 
  certain 
  extent 
  magnesia, 
  

   in 
  the 
  mother-liquor 
  of 
  basic 
  magmas 
  does 
  not 
  appear 
  to 
  have 
  

   attracted 
  the 
  attention 
  which 
  it 
  deserves. 
  It 
  shows 
  that 
  progressive 
  

   crystallization 
  in 
  these 
  magmas 
  sometimes 
  leads 
  to 
  a 
  result, 
  the 
  

   opposite 
  of 
  that 
  observed 
  in 
  the 
  case 
  of 
  intermediate 
  magmas 
  in 
  

   which 
  ferriferous 
  compounds 
  separate 
  out 
  during 
  the 
  early 
  phases 
  of 
  

   consolidation. 
  3 
  The 
  synthetic 
  experiments 
  of 
  Messrs. 
  Fouque 
  & 
  

   Levy 
  4 
  indicate 
  that 
  the 
  formation 
  of 
  magnetite 
  is 
  not 
  limited 
  to 
  one 
  

   period 
  in 
  the 
  history 
  of 
  the 
  consolidation 
  of 
  silicate-solutions, 
  and 
  the 
  

  

  1 
  Lemberg 
  examined 
  the 
  effect 
  of 
  water 
  and 
  solutions 
  of 
  alkaline 
  carbonates 
  

   on 
  volcanic 
  glasses. 
  He 
  says: 
  — 
  'Fassen 
  wir 
  alles 
  zusaminen, 
  so 
  werden 
  

   basische 
  Glaser 
  (Palagonitglas, 
  Tachjlyt) 
  schon 
  durch 
  reines 
  Wasser 
  bydra- 
  

   tisirt; 
  durch 
  Alkalicarbonate 
  werden 
  auch 
  sauere 
  Glaser 
  sehr 
  rasch 
  umge- 
  

   wandelt 
  ; 
  dabei 
  wird 
  Wasser 
  aufgenommen, 
  Alkali 
  gpgen 
  andere 
  starke 
  Basen 
  

   ausgetauscht, 
  Kieselsaure 
  zum 
  Tkeilausgeschieden 
  ' 
  ('Zur 
  Keimtnissder 
  Bildung 
  

   und 
  Uuiwandlung 
  von 
  Silicaten,' 
  Zeitschr. 
  Deutsch. 
  gsol. 
  Gesellseh. 
  voL 
  xxxv. 
  

   1883, 
  p. 
  -557). 
  

  

  2 
  See 
  W. 
  VV. 
  Watts, 
  ' 
  Guide 
  to 
  the 
  Collections 
  of 
  Rocks 
  and 
  Fossils 
  in 
  the 
  

   Museum 
  of 
  Science 
  and 
  Art, 
  Dublin,' 
  1895, 
  p. 
  78. 
  

  

  3 
  ' 
  On 
  some 
  Quartz-f'elsites 
  and 
  Augite-granites 
  from 
  the 
  Cheviot 
  District,' 
  

   Geol. 
  Mag. 
  1885, 
  p. 
  106. 
  

  

  4 
  ' 
  Synthese 
  des 
  Mineraux 
  et 
  des 
  Ro. 
  hes,' 
  Paris, 
  1882. 
  

  

  