Ledger Formation

The Ledger Formation or Ledger Dolomite is a geologic formation in Pennsylvania, United States.

Ledger Formation
Stratigraphic range: Cambrian
Sample of Ledger Formation from West York, Pennsylvania
Type	Formation
Sub-units	Lower dolomite member, Willis Run Member, upper dolomite member
Overlies	Kinzers Formation
Lithology
Primary	dolomite
Location
Region	Pennsylvania
Country	United States
Extent	Pennsylvania, Maryland, Virginia
Type section
Named by	Stose, G.W., and Jonas, A.I.[1]

The Ledger is described as light-gray, locally mottled, massive, pure, coarsely crystalline dolomite. It may be siliceous in the middle part.^[2]

Type section

Named from exposures at Ledger, Pennsylvania, formerly 3 miles northeast of Kinzers, Lancaster County, Pennsylvania.^[1]

Other outcrops

Harpers Formation thrust northwestward over Ledger Formation at left, Pottery Hill, southwest of York, in 1930

At Valley Forge National Historical Park, the visitor center parking lot is built within an old quarry of the Ledger, and the former quarry walls are exposed. The rocks contain stromatolites. In the nearby Port Kennedy Quarry, the Triassic Stockton Formation unconformably overlies the folded Ledger.^[3]

Outcrop at Valley Forge

The Harpers Formation overlies the Ledger Formation due to a thrust fault in small roadside quarry (currently overgrown) on Pottery Hill, southwest of York, as shown in the historical photo at left.^[4]

The Ledger is exposed at a roadcut on the south side of Route 30 at the interchange with Route 23 (East Walnut Street) on the northeast side of Lancaster.

Quarries

The quarry currently operated by Vulcan Materials Company in Edgegrove, Pennsylvania (west of Hanover) primarily mines the Ledger Formation for aggregate.^[5]