Interval is a northwestern limestone facies that correlates with dolomite strata (Tete des Morts, Blanding, lower Hopkinton formations) to the south and east. Sw forms the highest Silurian unit throughout most of its extent, generally overlain by Dw; locally interfingers with Sh dolomite strata to south. Primary lithology: limestone, dense, fossiliferous. Secondary lithologies: limestone, dense, cherty to very cherty; dolomitic limestone, dense; dolomite (locally at base). Minor: dolomite, silty to sandy (locally at base above Om). Maximum thickness, 80 ft (25 m).