In northern Rhode Island, consists of gray to black, fine- to coarse-grained quartz arenite, litharenite, shale, and conglomerate, with minor beds of anthracite and meta-anthracite. In southern Rhode Island, consists of meta-sandstone, meta-conglomerate, schist, carbonaceous schist, and graphite. Plant fossils are common.
Pink to gray, coarse-grained, equigranular rock composed of microcline, perthite, plagioclase, quartz, and accessory biotite, sphene, zircon, and opaque minerals; secondary chlorite and muscovite. Generally massive, but locally foliated and lineated. Includes some rock mapped formerly as Bulgarmarsh Granite and Metacom Granite Gneiss.
Gray, pink, or greenish, generally massive, coarse-grained, porphyritic (microcline phenocrysts) granite. Contains microcline, perthite, plagioclase, quartz, and accessory biotite, hornblende, apatite, sphene, and opaque minerals; secondary chlorite, epidote, and sericite. Includes some rock mapped formerly as Bulgarmarsh Granite and Newport Granite Porphyry.
Gray to green, fine-grained, thinly bedded schist consisting of muscovite, biotite, chlorite, and quartz. Locally contains think beds of quartzite, marble, and amphibolite. Includes rock mapped formerly as mica schist of Bristol, chlorite-biotite schist of Tiverton, and mica-chlorite schist of Sakonnet.
Buff to pale-gray conglomerate. Clasts consist entirely of quartzite; matrix primarily quartz, plus sparse amounts of magnetite. Cobbles and boulders are ubiquitously elongate, due to pressure-solution phenomena associated with deformation.
Buff siltstone at base grading upward into black to gray phyllite; units commonly cyclically repeated. Intimately interstratified with OCAcj, such that the two units are grouped together at the presented map scale.
Fine-grained graded beds of feldspathic siltstone and sandstone, interstratified with carbonate conglomerate, and ash-flow and lapilli tuff; some units may be lahar deposits.
Gray, smoky-quartz granule-conglomerate, sandstone, and pebble to cobble conglomerate, interbedded with black carbonaceous phyllite. Includes some rock mapped formerly as Pondville Conglomerate.
Sequences of gray, green, and maroon graded rocks, ranging from fine-grained feldspathic granule-conglomerate to maroon slate.
Dark gray phyllite, commonly with rhythmically bedded Bouma sequences and brown-weathering carbonate beds that contain concretions 10-30 cm long.
Consists of associations of the above rock types.
Large clasts of dolostone and quartz arenite (olistoliths) enclosed within a matrix of tuff, siltstone, slate, and conglomerate; interpreted as an olistostrome.
Green to black phyllite interstratified with buff to pink siltstone; trilobite-bearing.
Red, orange-brown, and gray-green phyllite and thinly-bedded, nongraded sandstone and siltstone; rare limestone, and sparse volcanic rock including welded-tuff.
Olive-gray to pale-gray, 1- to 4-m-wide dikes, mostly massive and porphyritic, but locally schistose, composed of biotite phenocrysts in a fine-grained groundmass of microcline, plagioclase, and quartz. Contains accessory apatite and pyrite, and secondary chlorite, sericite, calcite, and opaque minerals.
Light-gray, medium-grained, biotite granite, in part mafic-poor. Gneissic in New Bedford area. Includes Bulgarmarsh Granite (Proterozoic Z). Intrudes Zgs. Fall River pluton of the MA State map (Zen and others, 1983) is here referred to as the Fall River Granite. According to the authors, the change in name is meant to indicate the heterogeneous nature of the granite and the fact that it may consist of more than a single pluton. Included in this unit is the Bulgarmarsh Granite of Fall River and a mass of alaskitic gneiss shown on the State map south of Fall River. No type section is designated. Geologic map shows the Fall River present in the New Bedford area of MA and RI and bounded on the west by the Narragansett Bay Group. The Fall River was dated by Zartman and Naylor (1984) at about 600 Ma (U-Th-Pb zircon) (Murray and others, 1990).
Pink to buff-white, thinly laminated marble units (~ 3 m thick) containing diagnostic hyoliths, interlayered with magenta slate. The basal marble varies from pink to red to orange, whereas the overlying 15-m-thick phyllite varies from maroon and red to green, gray and silver. Intimately associated spatially with OCAcj, such that the two units are grouped together at the presented map scale.
Greenish-gray to gray-black, fine-grained, commonly porphyritic, generally massive dike rock composed of plagioclase, augite, opaque minerals, olivine pseudomorphed by serpentine and chlorite minerals, and sparse quartz.