The Frederick Valley is a narrow limestone valley, less than 25 miles long, lying east of the Catoctin Mountain-Blue Ridge uplift, which separates the Frederick Valley from the Hagerstown Valley to the west. The crystalline rocks of the Piedmont Plateau border the valley on the east, and Triassic sedimentary rocks cut it off on the north and south and border it on the west.
The valley sides contain blue slaty Frederick limestone; massive, purer Grove limestone occupies its center. The Frederick limestone rests on the Lower Cambrian Antietam quartzite on the east side of the valley.
Philip T. Tyson1 first suggested that the Frederick limestone is of Chazyan and Black River age. Keyes,2 in 1890, reported that brachiopods collected in the valley were of Chazyan or Trenton age. In his 1919 report on the Cambrian and Ordovician of Maryland, Bassler3 concluded that the Frederick limestone was probably of Chazyan . . .