The “Stones River” group of Maryland and adjacent States has been studied in light of recent classifications of the Middle Ordovician. The term St. Paul group (new), proposed as a substitute for the erroneously applied “Stones River” group, contains two formations, a lower, Row Park limestone (new), and the overlying New Market limestone. The Row Park limestone forms a wedge whose thin edge lies in West Virginia, thickening to an observable maximum in southern Pennsylvania. The formation includes dark, granular limestone bordering dove vaughanites on the south, east, and north. The New Market limestone was traced from Virginia, through West Virginia and Maryland, to southern Pennsylvania; it thickens in Maryland and southern Pennsylvania at the same rate and in the same direction as the Row Park limestone. The New Market is primarily dove vaughanite in southern areas, but considerable amounts of darker and magnesian limestones form the lower part of the formation north of the Potomac River.
The Row Park limestone fauna suggests correlation with type Lenoir limestone of northeastern Tennessee, and its equivalents in Virginia, and with the Chazy limestone of New York.
Corals dominate the fauna of the New Market; this fauna suggests correlation with the Pamelia limestone of New York and Ontario and with the Five Oaks limestone of the southern Appalachians.