Middle Cambrian trilobites of Acado-Baltic affinities have been found in southern Narragansett Bay, Rhode Island, in phyllites previously mapped as part of the Pennsylvanian stratigraphy of the Narragansett Basin. The trilobite-bearing phyllites form the basal unit of an approximately 1-km-thick sequence that has undergone four episodes of folding and cleavage formation.

Three different trilobites are represented. Badulesia tenera (Hartt), which gives a diagnostic medial Middle Cambrian age, is also known from New Brunswick, eastern Newfoundland, southern Germany, northern Spain, and eastern Turkey. This species in northern Spain characterizes a subzone within the Middle Cambrian Badulesia zone correlating approximately with the lower part of the Paradoxides paradoxissimus zone of northern Europe.

Nearby in Newport, Rhode Island, a sequence of maroon and green clastic sediments rests unconformably on Precambrian igneous rocks and sediments. If these should be proven to be Lower Cambrian, this succession in southern Narragansett Bay would be the most complete Cambrian succession yet recognized in southern New England and possibly a nearly complete record of sedimentation for this area for the entire Cambrian Period.

These well-exposed rocks are part of a distinctive succession of upper Precambrian and lower Paleozoic rocks and are interpreted as a fragment of the Avalonian platform or microcontinent, closely related to rocks of the eastern margin of the northern Appalachians and the western margin of western Europe.

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