The northern Appalachian Piedmont is underlain by metamorphosed sedimentary and igneous rocks. The sedimentary origin of many of these rocks was established during the late 1800's. Other rocks, particularly the massive inclusion-bearing metasediments (diamictites), were considered to be xenolithic granites until the 1940's or later.
Relict sedimentary textures and structures are preserved in some Piedmonst metasediments despite sillimanite-grade metamorphism. Few sedimentary structures, other than bedding, were reported until the early 1960's, when graded bedding and sequences of sedimentary structures resembling the Bouma Cycle, characteristic of turbidity current deposits, were reported front metagraywackes in the Maryland Piedmont. The metagraywackes are now interpreted as submarine fan deposits. Few of the metasediments have been studied from a sedimentologic viewpoint. Most of our knowledge of the sedimentary structures and depositional environments has been contributed by igneous and metamorphic petrologists, primarily George W. Fisher and Clifford A. Hopson. Sedimentologists (Juergen Reinhardt and Gregory S. Gohn) working in the Piedmont have dealt primarily with lower metamorphic grade carbonate rocks in the western and northwestern Piedmont.