﻿Smyth, 
  Jr. 
  — 
  Composition 
  of 
  the 
  Alkaline 
  Rocks. 
  33 
  

  

  Art. 
  Y. 
  — 
  The 
  Chemical 
  Composition 
  of 
  the 
  Alkaline 
  Rocks 
  

   and 
  its 
  Significance 
  as 
  to 
  their 
  Origin; 
  by 
  C. 
  H. 
  Smyth, 
  Jr. 
  

  

  As 
  the 
  alkaline 
  rocks 
  constitute 
  one 
  of 
  two 
  closely 
  related 
  

   groups 
  which, 
  taken 
  together, 
  comprise 
  all 
  igneous 
  rocks, 
  it 
  is 
  

   evident 
  that 
  any 
  complete 
  discussion 
  of 
  the 
  question 
  of 
  their 
  

   origin 
  must 
  involve 
  a 
  consideration 
  of 
  the 
  origin 
  of 
  igneous 
  

   rocks 
  in 
  general, 
  leading, 
  thus, 
  to 
  the 
  largest 
  problems 
  of 
  

   structural 
  and 
  dynamic 
  geology, 
  even 
  including, 
  in 
  the 
  last 
  

   analysis, 
  the 
  origin 
  and 
  internal 
  constitution 
  of 
  the 
  earth. 
  This 
  

   being 
  the 
  case, 
  it 
  is 
  safe 
  to 
  conclude 
  that 
  a 
  final 
  solution 
  of 
  the 
  

   problem 
  will 
  be 
  attained 
  only 
  by 
  a 
  long 
  series 
  of 
  approxima- 
  

   tions. 
  Recognizing 
  this 
  fact, 
  and 
  making 
  no 
  attempt 
  at 
  

   exhaustive 
  treatment, 
  the 
  present 
  discussion 
  deals 
  only 
  with 
  

   certain 
  phases 
  of 
  the 
  problem, 
  accentuating 
  relations 
  w 
  r 
  hose 
  

   significance 
  appears 
  to 
  be 
  greater 
  than 
  has 
  been 
  recognized 
  in 
  

   earlier 
  contributions. 
  

  

  The 
  title 
  of 
  this 
  paper, 
  and 
  of 
  others 
  dealing 
  with 
  the 
  same 
  

   problem, 
  would 
  seem 
  to 
  imply 
  that, 
  in 
  spite 
  of 
  their 
  broad 
  

   relations, 
  the 
  alkaline 
  rocks 
  have 
  something 
  distinctive 
  in 
  their 
  

   character 
  which 
  justifies 
  their 
  more 
  or 
  less 
  independent 
  con- 
  

   sideration 
  ; 
  and 
  it 
  need 
  hardly 
  be 
  said 
  that 
  this 
  appears 
  in 
  the 
  

   facts 
  that 
  they 
  are 
  marked 
  by 
  comparative 
  rarity 
  and 
  by 
  certain 
  

   peculiarities 
  of 
  chemical 
  and 
  mineralogical 
  composition. 
  

  

  The 
  comparative 
  rarity 
  of 
  the 
  alkaline 
  rocks, 
  as 
  contrasted 
  

   with 
  the 
  subalkaline 
  rocks, 
  has 
  been 
  generally, 
  though 
  often 
  

   tacitly, 
  recognized 
  by 
  penologists. 
  Subalkaline 
  rocks 
  are 
  

   taken 
  as 
  a 
  matter 
  of 
  course, 
  as 
  the 
  normal 
  and 
  expected 
  thing, 
  

   but 
  every 
  newly 
  discovered 
  occurrence 
  of 
  alkaline 
  rocks 
  is 
  

   made 
  the 
  object 
  of 
  special 
  study, 
  as 
  something 
  out 
  of 
  the 
  

   ordinary 
  and 
  of 
  unusual 
  interest. 
  

  

  A 
  more 
  precise 
  statement 
  of 
  this 
  quantitative 
  relation 
  has 
  

   recently 
  been 
  made 
  by 
  Daly,* 
  who, 
  after 
  careful 
  study 
  of 
  the 
  

   question, 
  concludes 
  that 
  the 
  alkaline 
  rocks 
  make 
  up 
  less 
  than 
  

   one 
  per 
  cent 
  of 
  all 
  igneous 
  rocks. 
  

  

  This 
  is 
  a 
  fact 
  of 
  much 
  importance 
  in 
  its 
  bearing 
  upon 
  the 
  

   origin 
  of 
  the 
  alkaline 
  rocks, 
  and, 
  as 
  shown 
  by 
  Daly, 
  points 
  dis- 
  

   tinctly 
  to 
  the 
  conclusion, 
  supported 
  by 
  many 
  other 
  lines 
  of 
  

   evidence, 
  that 
  they 
  are 
  derivative 
  in 
  their 
  nature, 
  products 
  of 
  

   a 
  special 
  variation 
  of 
  the 
  normal 
  subalkaline 
  magma. 
  In 
  

   other 
  words, 
  the 
  earth's 
  crust 
  is 
  composed 
  essentially 
  of 
  rocks 
  

   which 
  are 
  products 
  of 
  the 
  normal 
  differentiation 
  of 
  subalkaline 
  

   magmas, 
  and 
  which 
  constitute 
  99 
  per 
  cent 
  of 
  the 
  95 
  per 
  cent 
  

  

  *B. 
  A. 
  Daly: 
  The 
  Origin 
  of 
  Alkaline 
  Eocks, 
  Bull. 
  Geol. 
  Soc. 
  Am., 
  xxi, 
  

   pp. 
  87-118, 
  1910. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XXXVI, 
  No. 
  211.— 
  July, 
  1913. 
  

   3 
  

  

  