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Figure F7. Thin section photomicrographs illustrating matrix-supported dark multicolor basalt breccia and fine-grained sediment in Subunit IIID and the underlying volcanic sequence. A, B. Dark multicolor basalt breccia (Sample 330-U1373A-6R-2, 39–43 cm; Thin Section 88) ([A] single polarized, [B] crossed polars). Matrix is composed of altered glass, and deposit is interpreted as a possible lahar deposit. C. Volcanic sandstone (Sample 330-U1373A-9R-2, 76–79 cm; Thin Section 100) (single polarized), displaying fine-grained fragments of altered volcanic glass coated by calcite cement. Sediment is interpreted as a possible lahar deposit partly mingled with a lava flow (see also “Igneous petrology and volcanology”).

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