The paper is the second in a discussion with Leo Ogniben. Three types of gypsum are considered: a type consisting of sharply defined small grains; a coarse selenitic type; and one consisting of poorly defined, complexly interrelated gypsum elements. The author interprets the first named as directly derived from hydration of anhydrite, and the last named as a stage in the development of selenite from the fine grained. Ogniben regards both as the product of crushing selenite. Bearing of remnants of anhydrite in gypsum, of sharp boundaries of fine-grained gypsum crystals, of phantoms of anhydrite in gypsum, and of the possible conditions of metamorphic changes in gypsum, on the origin of these materials, are discussed.

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