| Text Description: |
A 10-cm thick, coarse-grained, light gray-pink tephra layer in a 40-50 cm coal bed from near (northwest of) the mouth of Oam Gulch. The boundaries with the coal are slightly gradual. This sample contains about 40% delicate pumice fragments that could not have been reworked. Some fragments are slightly altered at the edges or interiors of the grains. Seven to 10% plagioclase. Hornblende is less abundant than plagioclase. It has strong blue-green pleochroism, and may also be slightly altered. Trace k-spar with sericite alteration, zircon, clear quartz, and biotite. |