﻿48 
  Washington 
  — 
  Igneous 
  Rocks 
  from 
  Smyrna, 
  etc. 
  

  

  Julia 
  at 
  the 
  north 
  end, 
  it 
  is 
  reddish. 
  It 
  is 
  highly 
  porphyritic, 
  

   resembling 
  the 
  Pagos 
  rock, 
  the 
  dacites 
  and 
  andesites 
  of 
  Aegina 
  

   and 
  Methana, 
  and 
  some 
  of 
  our 
  western 
  porphyries. 
  Pheno- 
  

   crysts 
  of 
  feldspar, 
  dark 
  biotite, 
  and 
  fewer 
  of 
  hornblende 
  (when 
  

   present) 
  are 
  thickly 
  scattered 
  through 
  the 
  tine-grained 
  ground- 
  

   mass, 
  without 
  any 
  evidence 
  of 
  flow 
  structure. 
  The 
  specific 
  

   gravity 
  of 
  the 
  freshest 
  specimen, 
  which 
  was 
  also 
  that 
  chosen 
  

   for 
  analysis, 
  was 
  found 
  to 
  be 
  2'525 
  at 
  17° 
  C. 
  It 
  is 
  thus 
  nota- 
  

   bly 
  lighter 
  than 
  the 
  Smyrna 
  rocks, 
  which 
  is 
  probably 
  to 
  be 
  con- 
  

   nected 
  with 
  its 
  higher 
  silica 
  content 
  and 
  more 
  vitreous 
  struc- 
  

   ture. 
  

  

  When 
  examined 
  in 
  thin 
  section 
  the 
  feldspar 
  phenocrysts 
  are 
  

   found 
  to 
  be 
  chiefly 
  of 
  plagioclase, 
  with 
  a 
  smaller 
  number 
  of 
  

   orthoclase. 
  In 
  the 
  former 
  the 
  extinction 
  angles 
  of 
  the 
  twin- 
  

   ning 
  lamellae 
  indicate 
  a 
  labradorite 
  of 
  the 
  composition 
  AbjAUj. 
  

   The 
  sanidines 
  are 
  distinguished 
  by 
  their 
  lack 
  of 
  multiple 
  twin- 
  

   ning 
  (even 
  Carlsbad 
  twins 
  being 
  rare), 
  their 
  lower 
  refractive 
  

   index 
  and 
  their 
  parallel 
  or 
  nearly 
  parallel 
  extinctions. 
  The 
  

   feldspars 
  are 
  very 
  clear 
  and 
  glassy, 
  and 
  contain 
  only 
  a 
  few 
  

   inclusions 
  of 
  glass 
  and 
  apatite, 
  with 
  very 
  rarely 
  a 
  crystal 
  of 
  

   biotite. 
  The 
  biotites 
  are, 
  when 
  fresh, 
  of 
  a 
  slightly 
  brownish 
  

   olive-green, 
  and 
  show 
  no 
  signs 
  of 
  magmatic 
  alteration. 
  In 
  the 
  

   reddish 
  specimens 
  they 
  are 
  browner 
  in 
  tone 
  and 
  are 
  somewhat 
  

   decomposed. 
  The 
  hornblende 
  phenocrysts 
  are 
  well-formed, 
  

   stout 
  prisms 
  of 
  a 
  dark, 
  olive-green 
  color, 
  pleochroic, 
  and 
  per- 
  

   fectly 
  fresh 
  and 
  unaltered. 
  Augite 
  phenocrysts 
  are 
  wanting 
  

   entirely. 
  

  

  The 
  groundrnass 
  varies 
  considerably 
  in 
  structure. 
  In 
  most 
  

   specimens 
  it 
  is 
  very 
  abundant 
  and 
  highly 
  vitreous. 
  It 
  is 
  more 
  

   or 
  less 
  hyalopilitic, 
  but 
  not 
  very 
  thickly 
  so, 
  through 
  the 
  presence 
  

   of 
  feldspar 
  laths, 
  which 
  are 
  mostly 
  plagioclase, 
  with 
  fewer 
  of 
  

   orthoclase. 
  In 
  one 
  or 
  two 
  slides 
  small 
  square 
  sections 
  of 
  ortho- 
  

   clase 
  are 
  abundant. 
  Along 
  with 
  the 
  feldspar 
  laths 
  are 
  shreds 
  

   of 
  biotite 
  and 
  some 
  magnetite 
  grains 
  and 
  apatite 
  needles, 
  but 
  

   no 
  augite 
  microlites. 
  The 
  glass 
  base 
  is 
  colorless 
  or 
  slightly 
  

   brown, 
  and 
  darker 
  brown 
  spherulites 
  are 
  often 
  present. 
  These 
  

   are 
  usually 
  irregular 
  in 
  outline 
  and 
  possess 
  a 
  radiate 
  structure, 
  

   showing 
  between 
  crossed 
  nicols 
  an 
  ill-defined 
  cross. 
  These 
  

   spherulites 
  are 
  especially 
  abundant 
  in 
  a 
  specimen 
  from 
  near 
  the 
  

   great 
  Zeus 
  Altar. 
  Perlitic 
  cracking 
  is 
  also 
  observable 
  in 
  many 
  

   slides. 
  In 
  a 
  few 
  cases, 
  as 
  near 
  the 
  Temple 
  of 
  Julia 
  and 
  south 
  

   of 
  the 
  Theatre, 
  the 
  base 
  is 
  microfelsitic 
  and 
  brownish 
  in 
  color, 
  

   probably 
  due 
  to 
  devitrification 
  through 
  decomposition. 
  

  

  For 
  the 
  accompanying 
  analysis 
  (No. 
  1) 
  by 
  the 
  writer, 
  the 
  

   freshest 
  specimen 
  was 
  selected 
  from 
  about 
  halfway 
  up 
  the 
  

   southeast 
  slope. 
  It 
  is 
  gray 
  and 
  contains 
  considerable 
  horn- 
  

   blende. 
  Lepsius's 
  analysis 
  is 
  added 
  for 
  comparison 
  (JSTo. 
  2). 
  

  

  