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The basal Wamsutta Formation of the Narragansett Basin, Massachusetts–Rhode Island, contains Ma rhyolite that is unexpectedly 60 m.yr. older than sedimentary strata containing late Pennsylvanian floras higher in the basin fill. The transitional alkalic geochemistry of the rhyolite and associated basalt signifies Late Devonian rifting pre‐dating major basin subsidence. Surface rifting was accompanied by voluminous alkalic intrusions of the 380–370 Ma Scituate Igneous Suite into Neoproterozoic basement west of the basin and by ductile extension along shear zones confined to the pluton and neighboring units. The Maritimes Basin and adjoining areas in Atlantic Canada experienced a similar mid‐Paleozoic history.