The Virgilian series is the youngest part of the Pennsylvanian

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

in the

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

n geologic classification series. During Virgilian times, the top of the Conemaugh and the entire ''Monongahela group'' were deposited. As with other

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

series, it comprises

cyclothem In geology, cyclothems are alternating stratigraphy, stratigraphic sequences of Marine (ocean), marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists who worked ...

s, or distinct cycles of

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

formation.

Monongahela cyclothems (youngest at top)

:Note: the names below are of the Conemaugh age, not Monongahela age *Upper Little Pittsburgh *Lower Little Pittsburgh *Little Clarksburgh *Elk Lick *Duquesne *Gaysport *Ames *Harlem *Upper Bakerstown *Anderson *Wilgus *Upper Brush Creek *Lower Brush Creek *Mason *Mahoning

References

Carboniferous geology of Pennsylvania Carboniferous System of North America {{US-geologic-formation-stub