﻿366 
  J. 
  P. 
  Iddings 
  — 
  Densities 
  of 
  Igneous 
  Rocks. 
  

  

  Taiarapu, 
  which 
  have 
  the 
  same 
  chemical 
  composition 
  as 
  

   the 
  dominant 
  lavas 
  of 
  those 
  volcanoes, 
  yielded 
  the 
  follow- 
  

   ing 
  values 
  for 
  their 
  specific 
  gravities 
  determined 
  in 
  bulk 
  : 
  

  

  Mean 
  

   From 
  core 
  at 
  head 
  of 
  Papenoo 
  Theralite 
  3-15 
  

  

  Valley, 
  Tahiti 
  : 
  Olivine-gabbro 
  3-18 
  3-19 
  

  

  Olivine-gabbro 
  (?) 
  3.20 
  

   Peridotite 
  3-21 
  

  

  From 
  core 
  at 
  head 
  of 
  Tautira 
  Theralite 
  3-10 
  

  

  VaUey, 
  Taiarapu: 
  Olivine-gabbro 
  3-12 
  3-20 
  

  

  Peridotite 
  3-39 
  

  

  These 
  results 
  show 
  a 
  reasonably 
  close 
  correspondence 
  

   between 
  the 
  determined 
  and 
  estimated 
  specific 
  gravities 
  

   for 
  the 
  rocks 
  of 
  these 
  islands, 
  and 
  furnish 
  a 
  value 
  con- 
  

   siderably 
  higher 
  than 
  that 
  derived 
  from 
  the 
  15 
  analyses 
  

   previously 
  considered, 
  which 
  gave 
  a 
  normative 
  density 
  of 
  

   only 
  2-96. 
  The 
  normative 
  density 
  found 
  in 
  this 
  way 
  for 
  

   the 
  province 
  of 
  these 
  South 
  Sea 
  Islands 
  is 
  noticeably 
  

   higher 
  than 
  those 
  which 
  have 
  been 
  estimated 
  for 
  Hawaii 
  

   and 
  Eeunion. 
  

  

  