﻿34 
  Smyth, 
  Jr. 
  — 
  Composition 
  of 
  the 
  Alkaline 
  Rocks 
  

  

  of 
  igneous 
  rocks 
  of 
  which 
  Clarke* 
  estimates 
  the 
  lithosphere 
  to 
  

   consist. 
  The 
  remaining 
  igneous 
  rocks, 
  amounting 
  to 
  only 
  one 
  

   per 
  cent, 
  are 
  derived 
  from 
  the 
  same 
  magmas, 
  but 
  are 
  products 
  

   of 
  some 
  exceptional 
  conditions 
  of 
  differentiation, 
  which 
  find 
  

   their 
  expression 
  in 
  the 
  peculiar 
  chemical 
  and 
  mineralogical 
  

   composition 
  of 
  the 
  resultant 
  alkaline 
  rocks. 
  

  

  These 
  relations 
  may, 
  perhaps, 
  be 
  made 
  clearer, 
  so 
  far 
  as 
  

   the 
  major 
  constituents 
  of 
  rocks 
  are 
  concerned, 
  by 
  a 
  com- 
  

   parison 
  of 
  the 
  composition 
  of 
  igneous 
  rocks 
  in 
  general 
  with 
  

   that 
  of 
  alkaline 
  rocks. 
  The 
  mean 
  composition 
  of 
  igneous 
  

   rocks 
  has 
  been 
  estimated 
  by 
  averaging 
  the 
  results 
  of 
  large 
  

   numbers 
  of 
  analyses, 
  and, 
  on 
  the 
  basis 
  of 
  somewhat 
  different 
  

   data, 
  Clarke, 
  Harker 
  and 
  Washington 
  have 
  arrived 
  at 
  the 
  

   results 
  given 
  below, 
  in 
  I, 
  II 
  and 
  III, 
  the 
  figures 
  in 
  each 
  case 
  

   being 
  recalculated, 
  by 
  Clarke, 
  to 
  one 
  hundred 
  per 
  cent, 
  on 
  a 
  

   water 
  free 
  basis. 
  

  

  

  i 
  

  

  II 
  

  

  III 
  

  

  IV 
  

  

  V 
  

  

  Si0 
  2 
  

  

  ... 
  61*82 
  

  

  60-76 
  

  

  58*96 
  

  

  59-19 
  

  

  62-46 
  

  

  Ti0 
  2 
  

  

  •75 
  

  

  •53 
  

  

  1-05 
  

  

  . 
  -81 
  

  

  •56 
  

  

  A1 
  2 
  3 
  

  

  ... 
  15-51 
  

  

  15-87 
  

  

  15-99 
  

  

  16-51 
  

  

  18-07 
  

  

  Fe,0, 
  

  

  2-67 
  

  

  4-92 
  

  

  3'37 
  

  

  3-02 
  

  

  2-24 
  

  

  FeO 
  

  

  3-45 
  

  

  2-78 
  

  

  3-93 
  

  

  4-17 
  

  

  2-31 
  

  

  MnO 
  

  

  

  

  

  

  .... 
  

  

  •13 
  

  

  •08 
  

  

  MgO 
  

  

  4-02 
  

  

  3-82 
  

  

  3-87 
  

  

  3-93 
  

  

  •97 
  

  

  CaO 
  

  

  4-96 
  

  

  4-97 
  

  

  5-28 
  

  

  6*47 
  

  

  2-57 
  

  

  Na 
  2 
  

  

  3-51 
  

  

  3-28 
  

  

  3-96 
  

  

  3-39 
  

  

  5-58 
  

  

  KO 
  

  

  3-04 
  

  

  2-85 
  

   •22 
  

  

  3-20 
  

   •3'7 
  

  

  2-12 
  

   •26 
  

  

  5*02 
  

  

  2 
  

  

  •27 
  

  

  •14 
  

  

  100-00 
  

  

  100-00 
  

  

  100-00 
  

  

  100-00 
  

  

  100-00 
  

  

  II 
  

  

  Average 
  Igneous 
  Rock, 
  Clarke, 
  F. 
  W., 
  Data 
  of 
  Geochemis- 
  

   try, 
  Bull. 
  491, 
  U. 
  S. 
  Geo!. 
  Survey, 
  p. 
  25, 
  1911. 
  

  

  Average 
  Igneous 
  Rock, 
  Harker, 
  A., 
  Tertiary 
  Igneous 
  Rocks 
  

   of 
  the 
  Isle 
  of 
  Skye, 
  Mem. 
  Geol. 
  Survey 
  United 
  Kingdom, 
  

  

  p. 
  416, 
  

   III 
  Average 
  

  

  1904. 
  

   Igneous 
  

  

  Rock, 
  Washington, 
  H. 
  S., 
  Chemical 
  

  

  Analyses 
  of 
  Igneous 
  Rocks, 
  Prof. 
  Paper, 
  U. 
  S. 
  Geol. 
  Sur- 
  

   vey, 
  No. 
  14, 
  p. 
  106, 
  1903. 
  

   IV 
  Average 
  Composition 
  of 
  89 
  Diorites, 
  Daly, 
  R. 
  A., 
  Average 
  

   Chemical 
  Composition 
  of 
  Igneous 
  Rock 
  Types, 
  Proc. 
  Am. 
  

  

  Acad. 
  Arts 
  and 
  Sci., 
  xiv, 
  p. 
  238, 
  1910. 
  

  

  Average 
  Composition 
  of 
  23 
  Alkaline 
  Syenites, 
  Daly, 
  R. 
  A.. 
  

   Op. 
  cit., 
  p. 
  220. 
  

  

  The 
  agreement 
  of 
  these 
  estimates 
  is 
  sufficiently 
  close 
  to 
  war- 
  

   rant 
  the 
  conclusion 
  that 
  they 
  must 
  afford 
  a 
  fair 
  approximation 
  

  

  * 
  Clarke, 
  F. 
  W.: 
  The 
  Data 
  of 
  Geochemistry, 
  Bull. 
  491, 
  U. 
  S. 
  Geol. 
  Survey, 
  

   p. 
  81, 
  1911. 
  

  

  