Question: The Mississippian Borden Formation is a mapped bedrock unit in a state that was originally part of what other state?

Context paragraphs:
Mahantango Formation: The Devonian Mahantango Formation is a mapped bedrock unit in Pennsylvania, New Jersey, New York and Maryland.  It is named for the North branch of the Mahantango Creek in Perry and Juniata counties in Pennsylvania.  It is a member of the Hamilton Group, along with the underlying the Marcellus Formation Shale.  South of Tuscarora Mountain in south central Pennsylvania, the lower members of this unit were also mapped as the Montebello Formation.

Huntley Mountain Formation: The Huntley Mountain Formation is a late Devonian and early Mississippian mapped bedrock unit in Pennsylvania, in the United States.

Mauch Chunk Formation: The Mississippian Mauch Chunk Formation (Mmc) is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia.  It is named for the township of Mauch Chunk, now known as borough of Jim Thorpe, Pennsylvania and for nearby Mauch Chunk Ridge where the formation outcrops.

Juniata Formation: The Ordovician Juniata Formation is a mapped bedrock unit in Pennsylvania and Maryland.  It is a relative slope-former occurring between the two prominent ridge-forming sandstone units: the Tuscarora Formation and the Bald Eagle Formation in the Appalachian Mountains.

Kentucky: Kentucky ( , ), officially the Commonwealth of Kentucky, is a state located in the east south-central region of the United States.  Although styled as the "State of Kentucky" in the law creating it, Kentucky is one of four U.S. states constituted as a commonwealth (the others being Virginia, Pennsylvania, and Massachusetts).  Originally a part of Virginia, in 1792 Kentucky became the 15th state to join the Union.  Kentucky is the 37th most extensive and the 26th most populous of the 50 United States.

Old Port Formation: The Devonian Old Port Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia, USA.  Members of the unit are also mapped in New Jersey and Virginia as parts of other formations or groups.  Current usage by U.S. Geological Survey (USGS), however, restricts the name Old Port Formation to Pennsylvania.

Rockwell Formation: The Rockwell Formation is a late Devonian and early Mississippian mapped bedrock unit in West Virginia, Maryland, and Pennsylvania, in the United States.

Borden Formation: The Mississippian Borden Formation is a mapped bedrock unit in Kentucky, Indiana, Illinois, Ohio, West Virginia, and Tennessee.  It has many members, which has led some geologists to consider it a group (for example in Indiana) rather than a formation (for example in Kentucky).

Pocono Formation: The Mississippian Pocono Formation (Mp) is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia, in the United States.  It is also known as the Pocono Group in Maryland and West Virginia,

Pottsville Formation: The Pennsylvanian Pottsville Formation is a mapped bedrock unit in Pennsylvania, western Maryland, West Virginia, and Ohio.  The formation is also recognized in Alabama.  It is a major ridge-former in the Ridge-and-Valley Appalachians of the eastern United States.  The Pottsville Formation is conspicuous at many sites along the Allegheny Front, the eastern escarpment of the Allegheny or Appalachian Plateau.

Supporting paragraphs: Borden Formation Kentucky
Answer: Virginia