600 WALTER H. BUCHER 
8. Silicates: Some hydrous iron silicates, as, for instance, the 
greenalite of the Lake Superior region, and hydrous iron-aluminum 
silicates, as, for instance, the chamosite of the Jurassic ‘‘ Minette” 
ores of Europe and the similar silicates of our Silurian ores, occur 
extensively in the odlitic form. ‘They show all characteristics of 
original gels. In the case of greenalite the tendency to aggregate 
into numerous spherical grains was evident in the experiment. 
Distinct odlitic structure is also seen in a specimen of fire clay, from 
the base of the Pottsville from an unknown locality in eastern 
Kentucky, which was presented to me by Dr. A. M. Miller. A 
similar occurrence was described by Dr. W. A. Tarr at the last 
meeting of the Geological Society of America. For the’ present 
the question must remain undecided if in these odlitic clays the 
binding substance is silica or a silicate.’ 
g. Iron disulphide: Only one case of an odlite has come to my 
attention in the formation of which pyrite seems to have had an 
independent part; that is, in which it is more than merely a mechan- 
ically enmeshed constituent or of secondary origin. In the upper 
Lias of Northwestern Germany there occur beds which consist 
partly of massive pyrite cementing the shells of belemnites and 
ammonites, and partly of nearly black limestone rich in pyrite, 
the two phases grading one into the other. In the black limestones 
oolites are found of a deep black color, measuring o.5-3.0 mm. 
in diameter, and consisting of sharply defined alternating layers 
(“shells”) of yellow pyrite and black calcium carbonate (soluble 
in cold HCl with effervescence).2 Spherical nodules of pyrite 
with a fibrous radiated structure are not uncommonly found 
in shales,1 and ordinary concretions are common. Recently a 
1C, R. Van Hise and C. K. Leith, ‘“‘The Geology of the Lake Superior Region,” 
U.S. Geol. Surv. Mon., LIT (1911), 522-25. 
2 Cf. Rogers, op. cit., p. 535 (‘imperfect pisolitic structure” in a clay consisting 
largely of the amorphous equivalent of crystalline kaolinite). A fire-clay containing 
‘small rounded bodies which are nearly pure alumina was described by Greaves— 
Walker in Trans. Amer. Ceram. Soc., VIII, 297; quoted from Ries, “Clays” (New 
York, 1914), 52-53- 
3T. Brandes, ‘“‘Die faziellen Verhatnisse des Lias zwischen Harz und Egge 
‘Gebirge,” etc., N. Jahrb. fiir Min., etc., Beil. Bd., XXXIV (1912), 301. 
4 For a good example see, for instance, E. M. Norregaard, Meddelelser fra Dansk 
Geol. Firen, XI (1906), 105. 
