Detailed mapping of exposed Ordovician strata on the shore of Douglas Lake, Tennessee, shows local relief of 140 feet on the post-Lower Ordovician erosion surface. Dolomite and chert conglomerates fill depressions on this surface. Disconformable relations at the base of the Middle Ordovician series are also known in the Appalachians south of Roanoke, Virginia, in central and eastern New York, and in many places throughout the world. This disconformity may be a reflection of a major orogenic episode.

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