Schade's work.-The most important contribution toward a satisfactory interpretation of the origin of odlites and related structures was made by a member of the medical faculty of the University of Kiel, H. Schade, in 1909 and 1910, in his papers on the origin of urinary calculi and on the formation of concrements.2 In these he demonstrated' experimentally that concretionary bodies form when a substance passes from the state of an emulsion colloid (or "emulsoid") to that of a solid, and that if

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... he change leads to the crystalline state the resulting structure is radial if the substance is pure; if, however, other substances, colloid or crystalloid, are precipitated along with it a concentric structure is developed. Corresponding with this law, natural holesterin gallstones, when 80o to 90 per cent pure, show a radial crystalline structure, while gallstones containing 25 per cent or less holesterin exhibit perfect concentric lamination. Observations on iron chloride.-A substance which lends itself well to a demonstration of the process involved, because it requires no special preparation, is the commercial hydrated iron chloride. A SA rock is called "o6litic," or an "oolite," if it contains or consists of small grains or units of dominantly concentric structure. A rock is called "spherulitic" (but not a spherulite) if it contains or consists of small grains or units of dominantly radial crystalline structure. An individual grain of a spherulitic rock is called a "spherulite." For an individual grain of an o6lite the term "ovulite" might be used, which appears to be preferable to Kalkowsky's "oioid" not only for symmetry's sake. In this paper the term "spherite " will be used for all grains of the same origin irrespective of their structure.