602 WALTER H. BUCHER 
precipitate or of a gel at the time when the sand grains were dropped 
into it. The pyrite, which forms part of the layers, must therefore 
represent the final crystalline product of a series of transformations 
starting, according to Doss’s interpretation, with the gel of hydrated 
iron monosulphide (FeSH.OH). This assumption is based on the 
experiments of Feld, who demonstrated that the iron monosulphide, 
which results from the action of hydrogen sulphide on iron salts, 
is changed within a few days into amorphous iron disulphide, 
when hydrogen sulphide is allowed to pass through it in the presence 
of free sulphur and a reducing agent! (conditions realized in the 
natural sapropels). 
In these experiments the precipitate of the monosulphide was of 
black color and voluminous. In changing into the disulphide it 
turned brown and settled into a compact mass on the bottom of the 
vessel, sharply separated from the liquid above and undisturbed 
by the bubbles of hydrogen sulphide passing through it; it also 
formed a ‘‘mirror’’ of metallic brown color on the vertical walls of 
the vessel.” 
This sudden change in the physical properties of the precipitate 
of the monoxide, the sol of which is a typical suspensoid, certainly 
justifies the suspicion that the iron disulphide formed a gel, passing 
through an emulsoid state. 
It should be emphasized that any one of the substances referred 
to above may be present in an odlitic grain as the binding colloid 
or as an accidentally enmeshed crystalloid. The latter case is 
illustrated by many of the numerous organic odlitic structures, 
like animal and vegetal pearls, gallstones, urinary calculi, and 
many other similar bodies occasionally found in the tissues of the 
animal body, in which the percentage of organic substance, in 
those cases the binding colloid, is often very small. 
SIGNIFICANCE OF THIS INTERPRETATION 
This brief survey justifies the assumption that most, if not all, 
odlitic and spherulitic grains were formed by at least one constit- 
uent substance changing from the emulsoid state to that of a 
1W. Feld, Zeitschr. fiir angew. Chemie, XXIV (1911), 97-103. 
2 Feld, op. cit., p. Ior. 
