﻿Washmgton 
  — 
  Aiialyses 
  of 
  Italian 
  Volca^iic 
  Racks, 
  289 
  

  

  side, 
  eegirine 
  and 
  magnetite 
  grains, 
  and 
  little 
  or 
  no 
  glass. 
  No 
  

   sodalite 
  could 
  be 
  foand, 
  tbongli 
  it 
  is 
  undoubtedly 
  present. 
  Tbe 
  

   Arso 
  rock 
  is 
  tbe 
  well-known 
  black 
  one 
  witb 
  numerous 
  feldspar 
  

   pbenocrysts. 
  It 
  is 
  notable 
  througb 
  its 
  small 
  thougb 
  constant 
  

   content 
  of 
  olivine. 
  

  

  I 
  II 
  III 
  ll' 
  

  

  SiO^ 
  61-62 
  61-88 
  60-77 
  61-49 
  

  

  TiO, 
  0-87 
  0-69 
  

  

  Al.Og 
  1824 
  18-21 
  19-83 
  20*02 
  

  

  Fe^g 
  2-36 
  2-19 
  4-14 
  3-11 
  

  

  FeO 
  1-28 
  1-38 
  2'43 
  2-72 
  

  

  MnO 
  trace 
  trace 
  trace 
  0-01 
  

  

  MgO 
  0-56 
  0-61 
  0-34 
  0-52 
  

  

  CaO 
  1-44 
  1-15 
  1-63 
  1-88 
  

  

  Na,0 
  5 
  77 
  6-89 
  4-90 
  8-39 
  

  

  K^O 
  7-60 
  6-72 
  6-27 
  7-13 
  

  

  H^O 
  0-78 
  0-37 
  0-24 
  0*46 
  

  

  CI 
  0-15 
  0-30 
  

  

  P^O^ 
  trace 
  0-02 
  

  

  100-67 
  100-39 
  100-55 
  100-75 
  

  

  O 
  = 
  CI 
  -.- 
  0-03 
  0-07 
  

  

  100-64 
  100-32 
  

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

   II. 
  Trachyte, 
  Marecocco. 
  H. 
  S. 
  Washington 
  anal. 
  

  

  III. 
  Monte 
  Rotaro. 
  Fuchs 
  anal. 
  Min. 
  Petr. 
  Mitth., 
  1872, 
  p. 
  232. 
  

  

  IV. 
  Marecocco. 
  Fuchs 
  anal. 
  Min, 
  Petr. 
  Mitth., 
  1872, 
  p. 
  229. 
  

  

  The 
  two 
  analyses 
  (I 
  and 
  II) 
  resemble 
  each 
  other 
  very 
  closely, 
  

   except 
  in 
  the 
  alkalies, 
  though 
  the 
  total 
  amount 
  of 
  these 
  is 
  the 
  

   same. 
  They 
  are 
  typical 
  trachytes 
  rich 
  in 
  soda, 
  and 
  are 
  practically 
  

   identical 
  with 
  those 
  of 
  the 
  Phlegrsean 
  Fields, 
  as 
  was 
  to 
  be 
  

   expected 
  from 
  the 
  microscopical 
  examination. 
  The 
  rather 
  

   high 
  Ti02 
  is 
  to 
  be 
  noted, 
  as 
  well 
  as 
  the 
  CI 
  lower 
  than 
  in 
  the 
  

   preceding. 
  They 
  resemble 
  on 
  the 
  whole 
  the 
  analyses 
  of 
  Fuchs, 
  

   though 
  his 
  alkalies 
  are 
  considerably 
  lower. 
  It 
  is 
  probable 
  that 
  

   his 
  alkalies 
  are 
  too 
  low, 
  since 
  calculation 
  shows 
  that 
  about 
  two 
  

   per 
  cent 
  more 
  are 
  needed 
  to 
  satisfy 
  the 
  SiO^ 
  and 
  Al^Og 
  present. 
  

   Analysis 
  II, 
  of 
  the 
  holocrystalline 
  Marecocco 
  trachyte, 
  calcu- 
  

   lates 
  out 
  as 
  follows. 
  It 
  seems 
  probable 
  that 
  sodalite 
  is 
  rather 
  

   too 
  high, 
  since 
  it 
  was 
  not 
  seen 
  in 
  the 
  sections. 
  

  

  Orthoclase 
  39-5 
  

  

  Albite 
  __. 
  - 
  47-1 
  

  

  Sodalite 
  4-7 
  

  

  Diopside 
  . 
  _ 
  4*6 
  

  

  ^girine 
  1*4 
  

  

  Magnetite 
  2*7 
  

  

  100-0 
  

  

  