﻿Vol. 
  53.] 
  -ROCKS 
  AND 
  FOSSILS 
  FROM 
  FRANZ 
  JOSEF 
  LAND. 
  489 
  

  

  comparatively 
  late 
  period 
  in 
  the 
  history 
  of 
  consolidation. 
  Its 
  

   distribution 
  in 
  the 
  rock 
  is 
  in 
  accordance 
  with 
  the 
  view 
  that 
  

   progressive 
  crystallization 
  has 
  tended 
  to 
  concentrate 
  the 
  iron-oxides 
  

   in 
  the 
  mother-liqnor. 
  In 
  some 
  specimens 
  there 
  is 
  no 
  recognizable 
  

   magnetite, 
  the 
  whole 
  of 
  the 
  iron-oxide, 
  except 
  that 
  which 
  occurs 
  

   in 
  the 
  augite, 
  remaining 
  undifferentiated 
  in 
  the 
  brown 
  glass. 
  

   Microscopic 
  sections 
  of 
  the 
  amygdaloidal 
  varieties 
  show 
  the 
  connexion 
  

   between 
  the 
  interstitial 
  palagonite 
  and 
  that 
  which 
  partially 
  or 
  wholly 
  

   fills 
  the 
  vesicular 
  cavities. 
  There 
  is 
  perfect 
  continuity 
  between 
  the 
  

   two 
  kinds. 
  In 
  cases 
  of 
  partial 
  infilling 
  the 
  central 
  portion 
  of 
  the 
  

   cavity 
  is 
  occupied 
  by 
  calcite 
  (PI. 
  XXXVII, 
  fig. 
  2). 
  

  

  Many 
  specimens 
  of 
  more 
  or 
  less 
  decomposed 
  basalt 
  from 
  the 
  talus 
  

   fit 
  Cape 
  Flora 
  contain 
  beautiful, 
  radiating, 
  fibrous 
  aggregates 
  of 
  

   natrolite, 
  and 
  the 
  same 
  mineral 
  occurs 
  in 
  a 
  more 
  compact 
  form 
  in 
  

   concentric 
  concretions 
  filling 
  large, 
  irregular 
  cavities. 
  It 
  is 
  found 
  

   also 
  in 
  joints 
  in 
  rotten 
  basalt. 
  Analcime 
  occurs 
  in 
  detached 
  crystals, 
  

   sometimes 
  measuring 
  more 
  than 
  1 
  cm. 
  in 
  dinmeter, 
  and 
  also 
  as 
  

   aggregates 
  of 
  smaller 
  crystals. 
  The 
  analcime 
  of 
  these 
  rocks 
  appears 
  

   to 
  be 
  wholly 
  of 
  secondary 
  origin, 
  and 
  does 
  not 
  occur 
  as 
  in 
  the 
  

   monchiquites 
  and 
  analcime-basalts. 
  1 
  

  

  Agates 
  are 
  also 
  represented 
  in 
  the 
  collection, 
  and 
  one 
  large 
  

   specimen 
  of 
  chalcedony 
  and 
  quartz 
  which 
  was 
  evidently 
  formed 
  in 
  a 
  

   hollow 
  cavity 
  measures 
  about 
  20 
  x 
  12 
  X 
  10 
  cms. 
  

  

  Calcite 
  is 
  abundant 
  in 
  the 
  altered 
  varieties, 
  and 
  frequently 
  forms 
  

   the 
  infilling 
  material 
  of 
  the 
  araygdules, 
  occurring 
  either 
  alone 
  or 
  in 
  

   association 
  with 
  palagonite. 
  

  

  The 
  specimens 
  of 
  basalt 
  on 
  which 
  the 
  above 
  description 
  is 
  based 
  

   were 
  mainly 
  collected 
  near 
  Cape 
  Flora. 
  The 
  collection 
  includes 
  a 
  

   few 
  from 
  Hooker 
  Island 
  which 
  belong 
  to 
  the 
  same 
  type, 
  but 
  which 
  

   are 
  all 
  massive. 
  

  

  Two 
  or 
  three 
  points 
  still 
  remain 
  uncertain 
  with 
  reference 
  to 
  the 
  

   basaltic 
  formations 
  of 
  Franz 
  Josef 
  Land. 
  Judging 
  from 
  analogy 
  

   with 
  other 
  districts 
  of 
  similar 
  character, 
  we 
  should 
  expect 
  to 
  find 
  

   both 
  lava-flows 
  and 
  intrusive 
  sills. 
  Tuffs 
  and 
  agglomerates 
  are 
  

   rare 
  in 
  regions 
  of 
  plateau-basalt, 
  but 
  they 
  occasionally 
  occur 
  as 
  

   necks 
  and 
  as 
  beds 
  interstratifiod 
  between 
  successive 
  lava-flows. 
  

   Then 
  again 
  old 
  river-gravels 
  and 
  lake-deposits 
  are 
  sometimes 
  found 
  

   between 
  the 
  different 
  outpourings 
  of 
  basalt. 
  2 
  Have 
  we 
  evidence 
  

   of 
  similar 
  phenomena 
  in 
  Franz 
  Josef 
  Land 
  ? 
  Unfortunately 
  there 
  

   is 
  no 
  petrographical 
  character 
  by 
  which 
  sills 
  can 
  be 
  in 
  all 
  cases 
  

   distinguished 
  from 
  lavas 
  in 
  the 
  Brito-Arctic 
  province. 
  The 
  sills 
  are 
  

   usually 
  coarser 
  in 
  graiu, 
  columnar, 
  holocrystalline, 
  and 
  ophitic 
  in 
  

   structure, 
  but 
  none 
  of 
  these 
  characters 
  can 
  be 
  relied 
  upon 
  as 
  distinc- 
  

   tive. 
  Lavas 
  are 
  often 
  amygdaloidal, 
  but 
  amygdaloids 
  are 
  not 
  

   uncommon 
  in 
  sills 
  and 
  dykes. 
  

  

  1 
  ' 
  On 
  the 
  Monchiquites 
  or 
  Analcite 
  Group 
  of 
  Igneous 
  Rocks,' 
  L. 
  V. 
  Pirsson, 
  

   Journ. 
  Geol. 
  Chicago, 
  vol. 
  iv. 
  (1800) 
  p. 
  (57VI. 
  

  

  - 
  See 
  Sir 
  A. 
  Geikie'e 
  paper 
  on 
  the 
  ' 
  Tertiary 
  Basalt-plateaux 
  of 
  N. 
  W. 
  Europe,' 
  

   Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  lii. 
  (189)) 
  p. 
  331. 
  Future 
  observers 
  in 
  Franz 
  

   Josef 
  Ltfiid 
  would 
  do 
  well 
  to 
  study 
  this 
  paper. 
  

  

  