Casco Bay Group represents two distinct lithotectonic packages lying one to the east and one to the west of Flying Point fault. These are named respectively the Saco-Harpswell and Falmouth-Brunswick sequences. Cushing Formation is present in both sequences and is divided into 9 informal members. Those members lying west of the fault are distinctly different from those to the east. The Falmouth-Brunswick sequence (ascending) consists entirely of the Richmond Corner, Torrey Hill, Mount Ararat, and Nehumkeag Pond members of the Cushing Formation. In the Saco-Harpswell sequence of the Casco Bay Group, the Cushing consists of the (ascending) Peaks Island, Yarmouth Island, Merepoint, Bethel Point, and Wilson Cove members. In this eastern sequence, the Cushing underlies the informal Sebascodegan formation (rank raised), the Cape Elizabeth, Spring Point, Diamond Island, Scarboro, Spurwink, Jewell, and Macworth [Mackworth] Formations, all of Casco Bay Group. Age of the Cushing is considered to be Late Proterozoic to Ordovician. [Members of the Cushing were introduced in Hussey, 1985 (Maine Open File no. 85-87), and in the present report are still considered informal by the author.]

Source: GNU records (USGS DDS-6; Reston GNULEX).

An Rb-Sr whole-rock resetting age of 495+/-23 Ma (Olszewski and Gaudette, 1988) for the Cushing Formation suggests that the protoliths are at least as old as Cambrian.

Source: GNU records (USGS DDS-6; Reston GNULEX).