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The Geology of Delaware

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Outcrop Bc32-a: The Mt. Cuba Picnic Grove

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Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove

The Mt. Cuba Picnic Grove provides an opportunity to look at the gneisses and amphibolites of the Wissahickon Formation. The large boulders of gneiss lying beside the steps are peppered with dark-red garnets and elongated nodules of dull-white sillimanite. These sillimanite nodules (1/4" to 3/4" long) are abundant in the gneisses at Mt. Cuba and are an interesting feature of these highly metamorphosed sedimentary rocks. Alternating layers of gneisses and amphibolites crop out on the east side of the track. The gneisses show some typical upright folds and fractures. Contacts between the layers trend northeast, parallel to the regional trend of the Appalachians.

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Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove
Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove. The outcrop is covered with moss, but you can still see strong foliation and metamorphic layering.
Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove. Note the large open folds.
Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove. The waxy, white blobs are sillimanite nodules.
Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove. The waxy, white blobs are sillimanite nodules.
Rock Outcrop Bc32-a: The Mt. Cuba Picnic Grove. The waxy, white blobs are sillimanite nodules.