Ledger Formation
| 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 Formation or Ledger Dolomite is a geologic formation in Pennsylvania, United States.
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
[edit]Named from exposures at Ledger, Pennsylvania, formerly 3 miles northeast of Kinzers, Lancaster County, Pennsylvania.[1]
Other outcrops
[edit]
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]
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
[edit]The quarry currently operated by Vulcan Materials Company in Edgegrove, Pennsylvania (west of Hanover) primarily mines the Ledger Formation for aggregate.[5]
References
[edit]- ^ a b Stose, G.W., and Jonas, A.I., 1922. The lower Paleozoic section in southeastern Pennsylvania, Washington Academy of Sciences, Journal v. 12, no. 5, p. 358-366 [1]
- ^ Berg, T. M., Edmunds, W. E., Geyer, A. R., and others, compilers, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 1, 2nd ed., 3 sheets, scale 1:250,000.
- ^ Valley Forge National Historical Park, Montgomery and Chester Counties, The Geologic History, 2nd Ed, 1993. Pennsylvania Trail of Geology, Park Guide 8, Prepared by Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey [2]
- ^ A. J. Stose and G. W. Stose, 1944. Geology of the Hanover-York district, U. S. Geological Survey Professional paper 204.
- ^ Summary groundwater resources of Adams County, Pennsylvania by Taylor, L.E., and Royer, D.W., Pennsylvania Geological Survey. Water Resource Report 52. Map Scale: 1:50,000. 1981. link
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