. Bulletin of the Geological Society of America. Geology; Geology -- United States. Sl';:S AND 269 tridymite, can not be determined from the data available. The presence of tridymite is not decisive evidence of a temperature of formation al)ove 870°, for Fenner^^ has shown that it may crystallize as a metastable phase at relative low temperatures, especially in the presence of fluxes. In sonae of the outer cavities a later ferruginous staining has been in- troduced, ])ut this does not extend into the rock for anv distance, as is. FiGtjisE G.—Remarkable Lithophysw in
. Bulletin of the Geological Society of America. Geology; Geology -- United States. Sl';:S AND 269 tridymite, can not be determined from the data available. The presence of tridymite is not decisive evidence of a temperature of formation al)ove 870°, for Fenner^^ has shown that it may crystallize as a metastable phase at relative low temperatures, especially in the presence of fluxes. In sonae of the outer cavities a later ferruginous staining has been in- troduced, ])ut this does not extend into the rock for anv distance, as is. FiGtjisE G.—Remarkable Lithophysw in Oisidian Cube-shape oavity. Specimen 88431. Two-thirds natural size evident from tbc fact tbat the cavities on a iVesldy I'ractiii-ed surrafc do not show the slightest trace of such staining. To recapitulate: Specimen proves detinitcly tliat crystallization of radial spherulites took place as a result of the action of gases at high temperatures, at wliidi tiie obsidian was still soft and capable of flowing into fa\iti<'s whicb bail been sheared or had collapsed to a slight extent. 'J'br L-\ idencr of tbc presence of volatile components at high temperatures I'.\in. .lour. lii. vol. :;i;. :;, pp. .•{; Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Geological Society of America. [New York, etc. ] The Society
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