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Mr. A. C. DUNHAM drew attention to the similarities between the Skessa tuff and the Yellowstone tuff, recently described by F. R. Boyd (1961), who had determined the welding temperature experimentally (600° C). It was suggested that this temperature might be placed tentatively at the boundary between types 3 and 4 of the author’s classification of welded tuffs. The speaker asked the author to comment on the mode of emplacement of the tuff.
Dr. A. T. J. DOLLAR inquired about the kind and distribution of joints in the Skessa tuff, especially regarding any light they might throw on the manner and rate of loss of heat from the tuff and such broad indications as they might give about its likely viscosity and content of volatiles soon after eruption.
Were there columnar joints, as had been reported elsewhere in similar rocks1, and
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