Tomstown Dolomite
The Tomstown Dolomite or Tomstown Formation is a geologic formation in Maryland, Pennsylvania, Virginia and West Virginia. 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."
In southern Maryland it is divided into four members: