﻿46 
  Smyth, 
  Jr. 
  — 
  Composition 
  of 
  the 
  Alkaline 
  Rocks. 
  

  

  less 
  important. 
  The 
  strong 
  affinity 
  of 
  chlorine 
  for 
  the 
  alkali 
  

   metals, 
  particularly 
  sodium, 
  and 
  related 
  elements, 
  its 
  tendency 
  

   to 
  form 
  with 
  them 
  mobile 
  compounds, 
  its 
  presence 
  in 
  such 
  

   minerals 
  as 
  sodalite 
  and 
  noselite, 
  its 
  emission 
  from 
  volcanoes, 
  

   and 
  its 
  tendency, 
  mentioned 
  above, 
  to 
  be 
  concentrated 
  in 
  the 
  

   aqueous 
  extract 
  of 
  magmas, 
  are 
  all 
  suggestive 
  facts 
  in 
  this 
  con- 
  

   nection. 
  As 
  to 
  its 
  quantitative 
  sufficiency, 
  Clarke* 
  gives 
  a 
  

   percentage 
  of 
  0*20 
  in 
  his 
  average 
  composition 
  of 
  the 
  litho- 
  

   sphere, 
  ocean 
  and 
  atmosphere, 
  as 
  compared 
  with 
  0*19 
  for 
  car- 
  

   bon 
  (including 
  that 
  in 
  carbon 
  dioxide). 
  This 
  chlorine 
  is, 
  of 
  

   course, 
  mostly 
  in 
  solution 
  in 
  sea 
  water, 
  and 
  no 
  adequate 
  source 
  

   has 
  been 
  found 
  for 
  it 
  save 
  in 
  vulcanism.-f- 
  In 
  view 
  of 
  this 
  fact 
  and 
  

   the 
  well 
  known 
  chemical 
  potency 
  of 
  the 
  element, 
  there 
  is 
  reason 
  

   for 
  ascribing 
  to 
  it 
  a 
  considerable 
  part 
  in 
  the 
  segregation 
  of 
  

   alkaline 
  magmas. 
  

  

  The 
  remarkable 
  abundance 
  of 
  fluorite 
  in 
  certain 
  gold 
  telluride 
  

   deposits 
  associated 
  with 
  alkaline 
  rocks 
  suggests 
  fluorine 
  as, 
  in 
  

   some 
  cases, 
  an 
  active 
  agent 
  in 
  the 
  development 
  of 
  the 
  latter. 
  

  

  It 
  need 
  hardly 
  be 
  said 
  that, 
  throughout 
  this 
  paper, 
  the 
  term 
  

   'mineralizer' 
  has 
  been 
  employed 
  in 
  the 
  broad 
  sense 
  which 
  has, 
  

   of 
  late 
  years, 
  become 
  customary. 
  Though 
  not 
  strictly 
  in 
  

   accord 
  with 
  earlier 
  usage 
  and, 
  on 
  this 
  account, 
  somewhat 
  criti- 
  

   cised,;}; 
  such 
  broad 
  interpretation 
  of 
  the 
  term 
  is 
  often, 
  as 
  in 
  

   the 
  present 
  instance, 
  very 
  desirable. 
  

  

  To 
  sum 
  up 
  briefly, 
  in 
  conclusion 
  : 
  The 
  alkaline 
  rocks, 
  consti- 
  

   tuting 
  only 
  a 
  small 
  percentage 
  of 
  the 
  igneous 
  rocks 
  of 
  the 
  earth, 
  

   are 
  regarded 
  as 
  ultimately 
  derived 
  from 
  the 
  practically 
  univer- 
  

   sal 
  subalkaline 
  magma, 
  and, 
  from 
  their 
  relatively 
  high 
  content 
  

   of 
  rare 
  elements 
  and 
  mineralizers, 
  it 
  is 
  maintained 
  that 
  their 
  

   differentiation 
  has 
  been 
  largely 
  effected 
  through 
  the 
  agency 
  of 
  

   the 
  latter. 
  

  

  In 
  the 
  derived 
  alkaline 
  magma 
  there 
  is 
  a 
  concentration 
  of 
  

   the 
  agents 
  effecting 
  their 
  separation 
  and, 
  thus, 
  their 
  differen- 
  

   tiation 
  is 
  cumulative, 
  leading 
  to 
  great 
  diversity 
  of 
  composition, 
  

   with 
  fractions 
  relatively 
  rich 
  in 
  rare 
  elements. 
  

  

  While 
  the 
  localization 
  of 
  the 
  phenomena 
  may 
  be 
  subject 
  to 
  

   mechanical 
  control 
  and 
  have, 
  in 
  consequence, 
  a 
  tectonic 
  expres- 
  

   sion, 
  the 
  nature 
  of 
  any 
  such 
  relation 
  is 
  not, 
  at 
  present, 
  determin- 
  

   able. 
  

  

  The 
  problem 
  under 
  consideration 
  is 
  of 
  a 
  large 
  order 
  of 
  mag- 
  

   nitude 
  and 
  of 
  extreme 
  complexity, 
  but 
  it 
  is 
  hoped 
  that 
  the 
  

   foregoing 
  suggestions 
  may 
  prove 
  to 
  be 
  of 
  some 
  service 
  in 
  the 
  

   effort 
  to 
  accomplish 
  its 
  final 
  solution. 
  

  

  Princeton 
  University, 
  February, 
  1913. 
  

  

  *Op. 
  cit., 
  p. 
  33. 
  

  

  fCf. 
  Becker, 
  G. 
  F. 
  : 
  The 
  Age 
  of 
  the 
  Earth, 
  Smithsonian 
  Misc. 
  Contrib., 
  vol. 
  

   lvi, 
  No. 
  6, 
  p. 
  8, 
  1910. 
  

  

  X 
  Vogt, 
  J. 
  H. 
  L., 
  op. 
  cit. 
  p. 
  216. 
  

  

  