﻿Washington 
  — 
  A 
  nalyses 
  of 
  Italian 
  Volcanic 
  Rocks. 
  287 
  

  

  parallel 
  to 
  <i, 
  are 
  abundant, 
  their 
  borders 
  tending 
  to. 
  shade 
  off 
  

   into 
  the 
  groundmass. 
  Smaller, 
  longish 
  crystals 
  of 
  a 
  pale 
  green, 
  

   very 
  slightly 
  pleochroic 
  segirine-augite 
  are 
  very 
  abundant. 
  

   Few, 
  if 
  any, 
  of 
  the 
  separate 
  individuals 
  of 
  segirine 
  mentioned 
  

   by 
  Rosenbusch* 
  could 
  be 
  seen. 
  The 
  groundmass 
  proper 
  is 
  

   composed 
  of 
  small 
  rude 
  laths 
  and 
  anhedra 
  of 
  alkali-feldspar, 
  

   with 
  grains 
  of 
  magnetite 
  and 
  segirine-augite. 
  Interspersed 
  

   with 
  these 
  are 
  small, 
  colorless, 
  isotropic 
  anhedra, 
  which 
  gelati- 
  

   nize 
  with 
  HCl 
  and 
  stain 
  readily. 
  These 
  must 
  be 
  referred 
  to 
  

   sodalite, 
  which 
  the 
  analysis 
  shows 
  is 
  present 
  to 
  the 
  extent 
  of 
  

   about 
  ten 
  per 
  cent. 
  No 
  glass 
  base 
  could 
  be 
  found 
  and 
  the 
  

   specimen 
  analyzed 
  is 
  quite 
  holocrystalline. 
  A 
  dense, 
  black, 
  

   glassy 
  obsidian, 
  carrying 
  many 
  feldspar 
  phenocrysts, 
  is 
  also 
  

   found 
  at 
  the 
  locality 
  in 
  small 
  amount. 
  

  

  Yom 
  Rath 
  speaks 
  of 
  sodalite 
  in 
  the 
  groundmass 
  as 
  "unvoll- 
  

   kommen 
  ausgeschieden," 
  and 
  describes 
  the 
  sodalite 
  which 
  

   occurs 
  in 
  the 
  crevices 
  of 
  the 
  rock. 
  He 
  also 
  mentions 
  a 
  scapo- 
  

   lite-like 
  tetragonal 
  mineral 
  as 
  very 
  abundant 
  in 
  the 
  ground- 
  

   mass, 
  and, 
  from 
  his 
  analysis, 
  comes 
  to 
  the 
  conclusion 
  that 
  it 
  

   has 
  the 
  composition 
  of 
  oligoclase.f 
  My 
  microscopical 
  exami- 
  

  

  I 
  II 
  III 
  IV 
  V 
  

  

  SiO, 
  60-33 
  SQ-YQ 
  Gl-'Zl 
  b^'AI 
  61-23 
  

  

  TiO^ 
  trace 
  trace 
  

  

  A],0 
  18-74 
  lO-Yl 
  16-85 
  17-24 
  18-42 
  

  

  Fe.Og 
  2-84 
  2*95 
  427 
  4-33 
  .... 
  

  

  FeO 
  1-29 
  1-08 
  4-55 
  

  

  MnO 
  trace 
  trace 
  trace 
  

  

  MgO 
  0-38 
  0-36 
  0-99 
  0*99 
  0-34 
  

  

  CaO 
  1-15 
  1-19 
  1-51 
  3-10 
  1-81 
  

  

  Na,0 
  7-15 
  6-79 
  7-50 
  6-17 
  10-82 
  

  

  K,0 
  7-30 
  7-10 
  4-36 
  S'Ol 
  2-62 
  

  

  H^'O 
  0-56 
  0-24 
  1-05 
  1-07 
  0-16 
  

  

  Ci 
  0-43 
  0-53 
  0-65 
  1-03 
  0-78 
  

  

  100-17 
  99-74 
  98-89 
  101-41 
  100-73 
  

  

  = 
  C1--. 
  0-11 
  0-13 
  016 
  0-24 
  0-18 
  

  

  100-06 
  99-61 
  98-73 
  10ri7 
  100-57 
  

  

  I. 
  Trachyte, 
  Monte 
  Nuovo. 
  H. 
  S. 
  Washington 
  anal. 
  

   II. 
  Trachyte, 
  Monte 
  Cuma. 
  H. 
  S. 
  Washington 
  anal. 
  

  

  III. 
  Monte 
  Nuovo. 
  Abich 
  anal. 
  Abicb. 
  Vulk. 
  Erscb., 
  1841 
  

   p. 
  39. 
  Recalculated 
  in 
  Roth. 
  Gest. 
  Analysen, 
  1861, 
  p. 
  18, 
  

   No. 
  9. 
  

  

  IV. 
  Monte 
  Nuovo. 
  Rammelsberg 
  anal. 
  Roth. 
  Gesteins- 
  Analysen, 
  

   1861, 
  p. 
  18, 
  No. 
  10. 
  

  

  V. 
  Monte 
  Cuma. 
  Vom 
  Rath 
  anal., 
  op. 
  cit., 
  p. 
  610. 
  

  

  *Roseiibusch, 
  Mikr. 
  Phys., 
  ii, 
  1896, 
  p. 
  750. 
  

   f 
  Vom 
  Bath, 
  op. 
  cit., 
  pp. 
  608, 
  612. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  VIII, 
  No. 
  46.— 
  October, 
  1899. 
  

   20 
  

  

  