﻿and 
  its 
  Significance 
  as 
  to 
  their 
  Origin. 
  

  

  37 
  

  

  which, 
  though 
  small 
  in 
  amount, 
  are 
  thought 
  to 
  possess 
  a 
  

   peculiar 
  significance. 
  

  

  The 
  data 
  in 
  regard 
  to 
  these 
  minor 
  chemical 
  constituents 
  of 
  

   rocks 
  have 
  been 
  summarized 
  by 
  Washington* 
  in 
  an 
  exceedingly 
  

   interesting 
  and 
  suggestive 
  paper. 
  With 
  reference 
  to 
  the 
  rarer 
  

   elements, 
  he 
  concludes 
  that, 
  in 
  the 
  alkaline 
  rocks, 
  there 
  is 
  a 
  

   greater 
  relative 
  abundance 
  of 
  lithium, 
  beryllium, 
  cerium, 
  

   yttrium, 
  and 
  other 
  rare 
  earth 
  minerals, 
  zirconium, 
  uranium, 
  

   thorium, 
  sulphur 
  as 
  S0 
  3 
  , 
  fluorine, 
  chlorine, 
  barium 
  and 
  perhaps 
  

   tin. 
  In 
  the 
  subalkaline 
  rocks, 
  on 
  the 
  other 
  hand, 
  there 
  is 
  a 
  

   concentration 
  of 
  titanium, 
  vanadium, 
  manganese, 
  nickel 
  and 
  

   cobalt, 
  chromium, 
  platinum 
  metals 
  and, 
  possibly, 
  phosphorus. 
  

  

  A 
  tabulation 
  of 
  Washington's 
  somewhat 
  more 
  detailed 
  state- 
  

   ment, 
  giving 
  the 
  elements 
  concentrated 
  in 
  sodic, 
  potassic, 
  

   ferriferous, 
  magnesian 
  and 
  calcic 
  magmas, 
  respectively, 
  is 
  as 
  

   follows 
  : 
  

  

  Alkaline 
  

  

  Subalkaline 
  

  

  Sodium 
  

  

  Potassium 
  

  

  Iron 
  

  

  Magnesium 
  

  

  Calcium 
  

  

  Magmas 
  

  

  Magmas 
  

  

  Magmas 
  

  

  Magmas 
  

  

  Magmas 
  

  

  Li 
  

  

  Ba 
  

  

  ■Ti 
  

  

  Cr 
  

  

  Cr? 
  

  

  Be 
  

  

  

  Va 
  

  

  Pt 
  

  

  P? 
  

  

  Ce 
  

  

  

  Mn 
  

  

  

  

  Yt 
  

  

  

  Ni 
  

  

  

  

  Zr 
  

  

  

  Co 
  

  

  

  

  Ur 
  

  

  

  

  

  

  Th 
  

  

  

  

  

  

  S 
  (as 
  SO 
  s 
  ) 
  

  

  

  

  

  

  F 
  

  

  

  

  

  

  CI 
  

  

  

  

  

  

  !Sn? 
  

  

  

  

  

  

  The 
  contrast 
  between 
  the 
  two 
  main 
  sections 
  of 
  the 
  table 
  is 
  

   striking. 
  The 
  elements 
  of 
  the 
  second 
  section, 
  those 
  concen- 
  

   trated 
  in 
  subalkaline 
  magmas, 
  are 
  such 
  as 
  occur 
  in 
  ultrabasic 
  

   segregations, 
  nearly 
  always 
  in 
  basic 
  igneous 
  rocks. 
  On 
  the 
  

   other 
  hand, 
  the 
  elements 
  of 
  the 
  first 
  section, 
  those 
  concentrated 
  

   in 
  alkaline 
  magmas, 
  fall 
  into 
  two 
  groups 
  : 
  — 
  elements 
  character- 
  

   istic 
  of, 
  and 
  largely 
  confined 
  to, 
  pegmatites, 
  and 
  " 
  mineral- 
  

  

  izers. 
  

  

  The 
  frequent 
  association 
  of 
  these 
  two 
  latter 
  classes 
  of 
  elements 
  

   in 
  pegmatites 
  is 
  generally 
  recognized 
  as 
  having 
  a 
  direct 
  genetic 
  

  

  * 
  Washington, 
  H. 
  S. 
  : 
  The 
  Distribution 
  of 
  the 
  Elements 
  in 
  the 
  Igneous 
  

   Eocks, 
  Trans. 
  Am. 
  Inst. 
  M. 
  E., 
  xxxix, 
  pp. 
  735-764, 
  1909. 
  

  

  