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sandy shale, coal, and carbonaceous shale. Sandstone typically contains at least 40 percent subangular to subrounded quartz grains, 10 to 25 percent feldspar, and some mica and rock fragments, in a matrix of calcite, clay, and silt. Chert fragments constitute as much as 20 percent of some sandstones. Unoxidized rocks are mostly light gray but are light brown or buff where oxidized. The sandstone is weakly cemented, most commonly with calcite, but in places matrix silt and clay act as the binding agent. The sandstone and siltstone commonly are

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