﻿U. 
  S. 
  NATIONAL 
  MUSEUM 
  

  

  PROCEEDINGS, 
  VOL. 
  67, 
  ART. 
  7 
  PL. 
  2 
  

  

  

  

  I 
  

  

  7 
  

  

  Photomicrographs 
  of 
  Iddingsite-bearing 
  Rocks 
  

  

  For 
  explanation 
  of 
  plate 
  see 
  page 
  19 
  

  

  