Annual report of the Board of Regents of the Smithsonian Institution . ed 11diameters. Fig. 6. Part of same section, magnified 50 diameters, showing these charactersmore accentuated. Fig. 7. Heavy greenish-gray pumice from high up in the pumice the rock is composed of a dark, almost opaque network of microlithicmatter in which magnetite is abundantly distributed. The microliths arealmost hidden by the opacity of the magnetite and augite grains. Magnified 11diameters. Fig. 8. The thinnest possible section t9 make is sliown in this figure, magnified75 diameters, exhibiting the exten
Annual report of the Board of Regents of the Smithsonian Institution . ed 11diameters. Fig. 6. Part of same section, magnified 50 diameters, showing these charactersmore accentuated. Fig. 7. Heavy greenish-gray pumice from high up in the pumice the rock is composed of a dark, almost opaque network of microlithicmatter in which magnetite is abundantly distributed. The microliths arealmost hidden by the opacity of the magnetite and augite grains. Magnified 11diameters. Fig. 8. The thinnest possible section t9 make is sliown in this figure, magnified75 diameters, exhibiting the extensive indivdualization of the glass into opaquemicroliths. The leucite microliths are represented by spots of imperfectlytransmitted light where the crystal grains reach both sides of the slice, butare partially overlapped by augite and magnetite all around.* ° Had this specimen been chosen from the top of the essential ejecta of PhaseIII the thinnest section capable of being cut would have been opaque. It wastaken, therefore, from a transition stratum (see p. 312).. Smithsonian Report, 1909.—Johnston-Lavis. Plate 2.
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Keywords: ., bookauthorsmithsonianinstitutio, bookcentury1800, bookdecade1840
