﻿

  upon 
  the 
  surface 
  of 
  the 
  Earth. 
  495 
  

  

  This 
  wide 
  distribution 
  of 
  titanic 
  oxide 
  naturally 
  suggests 
  

   the 
  examination 
  of 
  the 
  rocks 
  themselves. 
  I 
  have 
  so 
  far 
  been 
  

   able 
  to 
  examine 
  only 
  the 
  following 
  typical 
  rocks, 
  the 
  localities 
  

   of 
  which 
  have 
  furnished 
  also 
  the 
  samples 
  for 
  analyses 
  already 
  

   published: 
  (73), 
  Trachyte, 
  Kiihlsbrunnen. 
  (74), 
  Trachyte. 
  

   (75), 
  Trachyte, 
  Drachenfels. 
  (76), 
  Hornblende 
  andesite, 
  Wol- 
  

   kenburg. 
  These 
  four 
  were 
  from 
  the 
  Siebengebirge. 
  (77), 
  

   Gabbro, 
  Radauthal, 
  Harzburg.* 
  (78), 
  Melaphyr, 
  Ilmenau, 
  

   Schneidemuller-berg. 
  (79), 
  Melaphyr, 
  Plauenschen 
  Grunde, 
  

   near 
  Dresden. 
  (80), 
  Nosean 
  phonolite, 
  Castle 
  Olbriick, 
  Laacher 
  

   See. 
  These 
  afford 
  the 
  following 
  : 
  

  

  Ti0 
  2 
  mentioned 
  in 
  published 
  analysis. 
  

   Zirkel, 
  II, 
  

  

  (73) 
  

  

  none 
  

  

  (74) 
  

  

  none 
  

  

  (75) 
  

  

  0-38 
  

  

  (76) 
  

  

  none 
  

  

  (77) 
  

  

  none 
  

  

  (78) 
  

  

  0-89 
  

  

  (79) 
  

  

  trace 
  

  

  (80) 
  

  

  none 
  

  

  analysis. 
  

  

  Ti0 
  2 
  found 
  

  

  p. 
  181 
  

  

  0-22 
  

  

  p. 
  182 
  

  

  0-86 
  

  

  p. 
  181 
  

  

  0'64 
  

  

  p. 
  212 
  

  

  1-14 
  

  

  p. 
  116 
  

  

  0-10 
  

  

  p. 
  55 
  

  

  1-01 
  

  

  p. 
  584 
  

  

  0-36 
  

  

  

  0-18 
  

  

  

  0-56 
  

  

  Zirkel 
  I, 
  

   Average 
  

  

  While 
  the 
  frequent 
  association 
  of 
  titanium 
  with 
  iron 
  (as 
  

   indicated 
  by 
  the 
  color 
  after 
  ignition), 
  in 
  these 
  soils 
  points 
  to 
  

   menaccanite 
  as 
  a 
  source 
  of 
  the 
  titanic 
  oxide 
  ; 
  yet 
  the 
  con- 
  

   siderable 
  amount 
  of 
  this 
  substance 
  in 
  some 
  of 
  the 
  clays 
  and 
  

   rocks 
  containing 
  little 
  iron 
  suggests 
  that 
  it 
  may 
  also 
  result 
  

   from 
  titanite 
  which 
  has 
  been 
  observedf 
  to 
  be 
  widely 
  dis- 
  

   tributed 
  in 
  igneous 
  rocks. 
  

  

  In 
  conclusion 
  I 
  desire 
  to 
  thank 
  those 
  who 
  have 
  assisted 
  me 
  

   in 
  this 
  work 
  by 
  supplying 
  the 
  desired 
  specimens. 
  

  

  Sept., 
  1891. 
  

  

  Art. 
  LI 
  V. 
  — 
  Notes 
  on 
  a 
  Missouri 
  Barite 
  ; 
  by 
  C. 
  Lcjedeking 
  

   and 
  H. 
  A. 
  Wheeler. 
  

  

  A 
  variety 
  of 
  barite 
  is 
  found 
  in 
  Pettis 
  County, 
  Mo., 
  that 
  

   presents 
  peculiar 
  chemical 
  and 
  crystallographic 
  characteristics. 
  

   It 
  occurs 
  in 
  clusters 
  of 
  simple 
  and 
  compound 
  crystals 
  that 
  

   individually 
  are 
  quite 
  perfect 
  and 
  which 
  vary 
  in 
  size 
  from 
  10 
  

   to 
  200 
  mm 
  in 
  length 
  by 
  1 
  to 
  30 
  mm 
  in 
  thickness 
  and 
  are 
  of 
  tabular 
  

   habit. 
  The 
  peculiarity 
  of 
  the 
  crystals 
  is 
  the 
  occurrence 
  of 
  

  

  *I 
  find 
  in 
  Bischoff 
  III, 
  page 
  467 
  : 
  Gabbro 
  from 
  Rodanthal 
  bei 
  Steinbruch, 
  con- 
  

   tains 
  Ti0 
  2 
  — 
  I 
  '75 
  per 
  cent. 
  

  

  f 
  Dana's 
  System 
  of 
  Mineralogy, 
  p. 
  389. 
  

  

  