| Tomstown Dolomite | |
|---|---|
| Stratigraphic range: Cambrian | |
 USGS photo 1 mile east of Bakerton, West Virginia | |
| Type | Sedimentary |
| Underlies | Rome Group and Waynesboro Formation |
| Overlies | Antietam Formation and Chilhowee Group |
| Thickness | 200 - 1000 feet |
| Lithology | |
| Primary | dolomite |
| Other | Chert, limestone, shale |
| Location | |
| Region | Appalachia, Mid-Atlantic United States, and Southeastern United States |
| Country | United States |
| Extent | Maryland, Pennsylvania, Virginia, [1] West Virginia |
The Tomstown Dolomite or Tomstown Formation is a geologic formation in Maryland, Pennsylvania, Virginia and West Virginia. [2] [3] [4] It preserves fossils dating to the Cambrian Period.
In Maryland it is described as "Interbedded light gray to yellowish-gray, thin- to thick-bedded dolomite and limestone; some shale layers; gradational contact with Antietam; thickness 200 to 1,000 feet." [2]
In southern Maryland it is divided into four members: [5]
- Dargan Member Interbedded and cyclical dolomite and limestone.
- Benevola Member Light gray to white, massive to poorly bedded, highly fractured sugary dolomite.
- Fort Duncan Member Medium- to dark-gray, thick bedded, mottled dolomite with white, void-filling sparry dolomite.
- Bolivar Heights Member Three lithologies from the basal layer of a tan, vuggy dolomite, to a light gray dolomitic marble called the Keedysville bed, to thin- to medium bedded layers of lime mudstone containing burrows.
