The Oella Formation is a Late Proterozoic or early Cambrian schist in Howard and Baltimore Counties, Maryland.

It is described as "Medium-grained biotite-plagioclase-muscovite-quartz schist, locally garnetiferous, interlayered on a centimeter to decimeter scale with fine-grained biotite-plagioclase-quartz gneiss, commonly bearing muscovite but less commonly garnet.

"[2] The type locality is along the Patapsco River at Oella, southwest Baltimore County.

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