﻿Washington 
  — 
  Igneous 
  Rocks 
  from 
  Smyrna, 
  etc. 
  43 
  

  

  are 
  not 
  as 
  common 
  as 
  diopside. 
  They 
  are 
  deep 
  brown, 
  strongly 
  

   pleoehroic, 
  and 
  basal 
  sections 
  show 
  a 
  slight 
  dispersion 
  of 
  the 
  

   axes 
  parallel 
  to 
  £(010). 
  They 
  are 
  quite 
  fresh 
  and 
  only 
  slightly 
  

   altered 
  on 
  the 
  edges 
  to 
  a 
  narrow 
  opacitic 
  border, 
  with 
  rounded 
  

   angles. 
  

  

  The 
  groundmass 
  in 
  general 
  is 
  typically 
  hyalopilitic, 
  the 
  

   microlites 
  being 
  mostly 
  of 
  labradorite, 
  with 
  fewer 
  of 
  what 
  

   seems 
  to 
  be 
  orthoclase, 
  some 
  small 
  colorless 
  diopside 
  prisms, 
  

   many 
  magnetite 
  grains, 
  and 
  a 
  few 
  small 
  crystals 
  of 
  apatite 
  and 
  

   zircon. 
  These 
  generally 
  show 
  flow-structure. 
  The 
  glass 
  base 
  

   is 
  usually 
  colorless, 
  though 
  sometimes 
  light 
  brown. 
  

  

  The 
  preceding 
  description 
  applies 
  especially 
  to 
  the 
  fresh 
  

   gray 
  specimens. 
  The 
  red 
  ones 
  show 
  much 
  the 
  same 
  features, 
  

   the 
  differences 
  being 
  due 
  to 
  decomposition. 
  Thus 
  in 
  these 
  the 
  

   augites 
  are 
  colored 
  red 
  or 
  black 
  on 
  the 
  edges, 
  the 
  biotites 
  are 
  a 
  

   dark 
  red 
  brown, 
  and 
  the 
  groundmass 
  is 
  much 
  decomposed 
  with 
  

   limonitic 
  products 
  very 
  abundant. 
  

  

  An 
  analysis 
  by 
  the 
  writer 
  of 
  a 
  typical, 
  fresh, 
  dark 
  gray 
  

   specimen 
  from 
  near 
  the 
  top 
  of 
  Mt. 
  Pagos 
  is 
  inserted 
  here. 
  Its 
  

   sp. 
  gr. 
  is 
  2-640 
  at 
  17° 
  C. 
  

  

  Si0 
  2 
  60-68 
  

  

  Al 
  2 
  3 
  16-19 
  

  

  Fe 
  2 
  3 
  5-37 
  

  

  FeO 
  1-58 
  

  

  MgO 
  _ 
  2-96 
  

  

  CaO 
  5-88 
  

  

  Na 
  2 
  8-11 
  

  

  K 
  a 
  O 
  3-95 
  

  

  H 
  2 
  0-98 
  

  

  - 
  300-70 
  

  

  It 
  it 
  high 
  in 
  silica 
  and 
  alkalies 
  for 
  an 
  andesite 
  and 
  with 
  

   rather 
  low 
  alumina. 
  The 
  potash 
  is 
  considerably 
  higher 
  than 
  

   soda, 
  which 
  would 
  account 
  for 
  the 
  presence 
  of 
  some 
  orthoclase 
  

   in 
  the 
  groundmass, 
  since 
  biotite 
  is 
  not 
  very 
  abundant, 
  though 
  

   part 
  of 
  it 
  may 
  belong 
  to 
  the 
  glass 
  base. 
  On 
  account 
  of 
  the 
  

   vitreous 
  character 
  of 
  the 
  rock 
  it 
  is 
  scarcely 
  practicable 
  to 
  calcu- 
  

   late 
  from 
  the 
  analysis 
  a 
  possible 
  mineralogical 
  composition. 
  

   There 
  is, 
  however, 
  more 
  Si0 
  2 
  than 
  enough 
  to 
  satisfy 
  all 
  the 
  

   other 
  constituents, 
  even 
  assuming 
  that 
  all 
  the 
  K 
  2 
  is 
  in 
  ortho- 
  

   clase, 
  which, 
  of 
  course, 
  is 
  not 
  the 
  case 
  ; 
  so 
  that 
  quartz 
  would 
  

   have 
  separated 
  out 
  if 
  the 
  rock 
  had 
  been 
  formed 
  under 
  condi- 
  

   tions 
  allowing 
  of 
  a 
  noncrystalline 
  development. 
  On 
  this 
  

   account 
  the 
  rock 
  might 
  be 
  properly 
  called 
  a 
  dacite. 
  

  

  The 
  rocks 
  of 
  Kara 
  Tash 
  (Black 
  Kock) 
  2 
  km 
  west 
  of 
  Smyrna, 
  

   three 
  specimens 
  of 
  which 
  were 
  sent 
  me 
  by 
  Mr. 
  Diller, 
  differ 
  

  

  