﻿and 
  its 
  Significance 
  as 
  to 
  their 
  Origin. 
  39 
  

  

  ments 
  occurring 
  in 
  pegmatites 
  associated 
  with 
  alkaline 
  rocks 
  in 
  

   whose 
  parent 
  magmas 
  the 
  elements 
  in 
  question 
  must 
  have 
  

   occurred 
  in 
  a 
  state 
  of 
  relative 
  concentration 
  as 
  compared 
  with 
  

   their 
  amounts 
  in 
  subalkaline 
  magmas. 
  

  

  Referring 
  to 
  cerium, 
  yttrium, 
  and 
  other 
  rare 
  earth 
  metals, 
  

   together 
  with 
  thorium 
  and 
  uranium, 
  Washington* 
  says 
  : 
  " 
  Min- 
  

   erals 
  containing 
  them 
  are 
  commonly 
  associated 
  with 
  acid 
  peg- 
  

   matites, 
  which, 
  judging 
  from 
  occurrences 
  in 
  Norway, 
  Green- 
  

   land 
  and 
  elsewhere, 
  are 
  most 
  apt 
  to 
  be 
  sodic, 
  though 
  the 
  few 
  

   determinations 
  available 
  of 
  the 
  rare 
  earths 
  are 
  in 
  highly 
  

   potassic 
  igneous 
  rocks." 
  Thus, 
  while 
  here, 
  as 
  elsewhere 
  in 
  the 
  

   paper, 
  Washington 
  distinguishes 
  between 
  sodic 
  and 
  potassic 
  

   magmas, 
  he 
  refers 
  the 
  elements 
  in 
  question 
  to 
  one 
  of 
  the 
  two., 
  

   or 
  in 
  other 
  words, 
  to 
  alkaline 
  magmas. 
  

  

  He 
  states 
  that 
  lithium 
  favors 
  the 
  sodic 
  rather 
  than 
  the 
  potas- 
  

   sic 
  magma, 
  while 
  beryllium 
  has 
  similar 
  associations. 
  " 
  Few 
  

   analyses 
  exist 
  of 
  such 
  beryl-bearing 
  rocks 
  and 
  beryllia 
  has 
  

   seldom 
  been 
  estimated 
  separately 
  from 
  alumina 
  in 
  rock-anal- 
  

   ysis, 
  but 
  such 
  data 
  as 
  are 
  available 
  and 
  the 
  common 
  mineralog- 
  

   ical 
  association 
  of 
  beryllium 
  and 
  sodium 
  point 
  to 
  the 
  conclusion 
  

   that 
  the 
  element 
  is 
  most 
  at 
  home 
  in 
  sodic 
  magmas." 
  

  

  Zirconium, 
  he 
  says, 
  "may 
  be 
  considered 
  to 
  be 
  a 
  characteristic 
  

   minor 
  chemical 
  constituent 
  of 
  the 
  sodic 
  rocks, 
  whether 
  the 
  

   silica 
  be 
  so 
  high 
  that 
  quartz 
  is 
  present, 
  or 
  whether 
  it 
  be 
  so 
  low 
  

   that 
  nephelite 
  is 
  abundant, 
  as 
  in 
  the 
  nephelite-syenites 
  and 
  

   phonolite." 
  

  

  In 
  the 
  case 
  of 
  fluorine 
  " 
  there 
  seems 
  to 
  be 
  a 
  marked 
  ten- 
  

   dency 
  on 
  its 
  part 
  to 
  favor 
  especially 
  rocks 
  which 
  are 
  high 
  in 
  

   soda. 
  This 
  is 
  seen 
  in 
  the 
  fact 
  that 
  fluorite 
  is 
  frequently 
  present 
  

   as 
  an 
  original 
  constituent 
  of 
  such 
  highly 
  sodic 
  rocks 
  as 
  nephe- 
  

   lite-syenite, 
  phonolite 
  and 
  tinguaite 
  ; 
  the 
  association 
  of 
  fluorine 
  

   and 
  sodium 
  in 
  certain 
  rare 
  minerals, 
  as 
  leucophanite, 
  meliphan- 
  

   ite, 
  johnstrupite, 
  rinkite, 
  etc., 
  which 
  are 
  almost 
  always 
  found 
  in 
  

   sodic 
  rocks 
  ; 
  and 
  by 
  the 
  recent 
  discovery 
  by 
  Lacroix 
  of 
  sodium 
  

   fluoride 
  in 
  nephelite-syenite 
  of 
  West 
  Africa." 
  

  

  " 
  Chlorine 
  resembles 
  fluorine 
  in 
  being 
  a 
  pneumatolytic 
  consti- 
  

   tuent, 
  and 
  is 
  present 
  in 
  igneous 
  rocks, 
  chiefly 
  in 
  the 
  minerals 
  

   sodalite 
  and 
  noselite, 
  which 
  are 
  almost 
  wholly 
  confined 
  to 
  sodic 
  

   rocks 
  and 
  especially 
  those 
  which 
  are 
  low 
  in 
  silica, 
  in 
  this 
  

   resembling 
  the 
  occurrence 
  of 
  S0 
  3 
  ." 
  

  

  These 
  extracts 
  from 
  Washington's 
  paper 
  serve 
  to 
  make 
  clear 
  

   the 
  general 
  abundance 
  of 
  rare 
  earths 
  and 
  related 
  elements, 
  and 
  

   of 
  the 
  mineralizers, 
  in 
  the 
  alkaline 
  rocks, 
  as 
  compared 
  with 
  the 
  

   subalkaline 
  rocks. 
  These 
  elements 
  may 
  be 
  perceptibly 
  abun- 
  

   dant 
  throughout 
  large 
  masses 
  of 
  alkaline 
  rocks, 
  or 
  they 
  may 
  

   appear 
  only 
  in 
  the 
  associated 
  pegmatites 
  as 
  a 
  result 
  of 
  concen- 
  

  

  * 
  Loc. 
  cit. 
  

  

  