Geologic units in Michigan (state in United States)

Additional scientific data in this geographic area

Coldwater Shale (Mississippian) at surface, covers 17 % of this area

Coldwater Shale

Saginaw Formation (Pennsylvanian) at surface, covers 13 % of this area

Saginaw Formation

Michigan Formation (Mississippian) at surface, covers 8 % of this area

Michigan Formation

Marshall Sandstone (Mississippian) at surface, covers 8 % of this area

Marshall Sandstone

Red beds (Jurassic) at surface, covers 5 % of this area

Red beds

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 4 % of this area

Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Antrim Shale (Late Devonian) at surface, covers 4 % of this area

Antrim Shale

Traverse Group (Middle Devonian) at surface, covers 4 % of this area

Traverse Group

Ellsworth Shale (Late Devonian) at surface, covers 3 % of this area

Ellsworth Shale

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 3 % of this area

Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Trenton Limestone (Late Ordovician) at surface, covers 3 % of this area

Trenton Limestone

Black River Limestone (Late Ordovician) at surface, covers 2 % of this area

Black River Limestone

Prairie du Chien Group (Early Ordovician) at surface, covers 2 % of this area

Prairie du Chien Group

Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 2 % of this area

Varied gneisses of mostly unknown age in cores of gneiss domes and fault-bounded uplifts (Archean gneiss terranes). Except for the Watersmeet dome (Late to Early Archean), all dated rocks are Late Archean. Includes granite of Late Archean age that transgresses gneisses and amphibolite.

Bayport Limestone (Mississippian) at surface, covers 1 % of this area

Bayport Limestone

Detroit River Group (Middle Devonian) at surface, covers 1 % of this area

Detroit River Group

Trempealeau Formation (Late Cambrian) at surface, covers 1 % of this area

Trempealeau Formation

Portage Lake Volcanics (Middle Proterozoic) at surface, covers 1 % of this area

Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Engadine Dolomite (Early Silurian) at surface, covers 1 % of this area

Engadine Dolomite

Munising Formation (Late Cambrian) at surface, covers 1 % of this area

Munising Formation

Gneiss and amphibolite (Late Archean) at surface, covers 1 % of this area

Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).

Burnt Bluff Formation (Early Silurian) at surface, covers 1 % of this area

Burnt Bluff Formation

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers 1 % of this area

Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Manistique Formation (Early Silurian) at surface, covers 0.9 % of this area

Manistique Formation

Utica Shale (Late Ordovician) at surface, covers 0.8 % of this area

Utica Shale

Stonington Formation (Late Ordovician) at surface, covers 0.8 % of this area

Stonington Formation

Dundee Limestone (Middle Devonian) at surface, covers 0.8 % of this area

Dundee Limestone

Bedford Shale (Late Devonian) at surface, covers 0.8 % of this area

Bedford Shale

Baraga Group; Michigamme Formation; Gray to black slate (Early Proterozoic) at surface, covers 0.5 % of this area

Strongly cleaved. Represents lower stratigraphic part of formation

Grand River Formation (Pennsylvanian) at surface, covers 0.5 % of this area

Grand River Formation

Big Hill Dolomite (Late Ordovician) at surface, covers 0.5 % of this area

Big Hill Dolomite

Queenston Shale (Late Ordovician) at surface, covers 0.4 % of this area

Queenston Shale

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers 0.4 % of this area

Red lithic conglomerate and sandstone; mafic to felsic volcanic flows similar to those of the unnamed formation (unit Yu) are interlayered with the sedimentary rocks.

Cataract Formation (Early Silurian) at surface, covers 0.4 % of this area

Cataract Formation

Berea Sandstone (Late Devonian) at surface, covers 0.4 % of this area

Berea Sandstone

Sunbury Shale (Mississippian-Devonian) at surface, covers 0.4 % of this area

Sunbury Shale

Menominee Group; Hemlock Formation (Early Proterozoic) at surface, covers 0.4 % of this area

Predominantly mafic to intermediate volcanic flows and pyroclastic rocks with interlayered slate and tuff beds

Puritan Quartz Monzonite (Late Archean) at surface, covers 0.3 % of this area

Pink to pinkish-gray, medium- to coarse-grained, equigranular to inequigranular granite to granodiorite in Puritan batholith south of Gogebic Range. Age 2710 +/- 140 Ma (Sims and others, 1977)

Porcupine Volcanics (Middle Proterozoic) at surface, covers 0.3 % of this area

Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Bois Blanc Formation (Early Devonian) at surface, covers 0.3 % of this area

Bois Blanc Formation

Metabasalt (Late Archean) at surface, covers 0.2 % of this area

Derived from mafic to intermediate pyroclastic rocks and massive to pillowed lava flows. Unit mapped as Ramsey Formation by Prinz (1981) south of Gogebic Range; mapped as Mona Schist and Kitchi Schist in northern complex of Marquette District.

Bass Island Dolomite (Late Silurian) at surface, covers 0.2 % of this area

Bass Island Dolomite

Point Aux Chenes Shale (Late Silurian) at surface, covers 0.2 % of this area

Point Aux Chenes Shale

Collingwood Limestone (Late Ordovician) at surface, covers 0.2 % of this area

Collingwood Limestone

Sylvania Sandstone (Early Devonian) at surface, covers 0.2 % of this area

Sylvania Sandstone

Paint River Group; Upper part (Early Proterozoic) at surface, covers 0.2 % of this area

Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Paint River Group; Lower part (Early Proterozoic) at surface, covers 0.1 % of this area

Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group

Menominee Group; Blair Creek Formation (Early Proterozoic) at surface, covers 0.1 % of this area

Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Chocolay Group, undivided (Early Proterozoic) at surface, covers 0.1 % of this area

In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation

Dickinson Group, undivided (Late Archean) at surface, covers 0.1 % of this area

Metavolcanic and metasedimentary rocks in Dickinson County, Mich. From youngest to oldest, consists of Six-Mile Lake Amphibolite, Solberg Schist, and East Branch Arkose.

Badwater Greenstone (Early Proterozoic) at surface, covers 0.1 % of this area

Dark-greenish-gray, pillowed to massive tholeiitic basalt and pyroclastic rocks. Correlated with the Hemlock Formation on basis of geology and similarity in chemical composition.

Porcupine Volcanics; Rhyolite (Middle Proterozoic) at surface, covers 0.1 % of this area

Porcupine Volcanics; Rhyolite

Menominee Group; unexposed magnetic unit (Early Proterozoic) at surface, covers < 0.1 % of this area

Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member (Early Proterozoic) at surface, covers < 0.1 % of this area

Poorly exposed. Includes Clarksburg Volcanics member which is mostly mafic to intermediate pyroclastic rocks in Marquette trough, between Marquette Bay and Champion

Menominee and Chocolay Groups, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Mapped where units are too thin to show separately on map

Salina Group (Late Silurian) at surface, covers < 0.1 % of this area

Salina Group

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Oronto Group; Nonesuch Shale (Middle Proterozoic) at surface, covers < 0.1 % of this area

Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

Bell Shale (Middle Devonian) at surface, covers < 0.1 % of this area

Bell Shale

Menominee Group, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Includes Negaunee Iron-formation, Siamo Slate, and Ajibik Quartzite in areas where units are too thin to map individually.

Menominee Group; Negaunee Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Highly metamorphosed banded iron-formation. Principal iron-formation in Marquette trough and nearby areas. Includes abundant metadiabase sills.

Metadiabase (Early Proterozoic) at surface, covers < 0.1 % of this area

Variably metamorphosed dikes, sills and subconcordant sheets of diabasic rocks. Probably coeval (in part) with volcanic rocks of Hemlock Formation (unit Xh)

Copper Harbor Conglomerate; Volcanic member (Early Proterozoic) at surface, covers < 0.1 % of this area

Basaltic to andesitic volcanic flows interbedded within the conglomerate and sandstone

Baraga Group; Copps Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Fine- to medium-grained graywacke and less abundant gray to black slate. Thin basal conglomerate west of Lake Gogebic contains clasts of underlying Archean rocks in a quartzitic and argillaceous matrix.

Menominee Group; Composite unit of Siamo Slate and Ajibik Quartzite (Early Proterozoic) at surface, covers < 0.1 % of this area

Siamo Slate is laminated green siltstone and argillite. Ajibik Quartzite is white, buff, and pink orthoquartzite and less abundant sericite quartzite.

Baraga Group; Volcanic-sedimentary unit (Early Proterozoic) at surface, covers < 0.1 % of this area

Interlayered fine- to medium-grained metasedimentary rocks and metavolcanic rocks in poorly exposed areas in southern Baraga County, Mich.

Menominee Group; Ironwood Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Metagraywacke (Late Archean) at surface, covers < 0.1 % of this area

Gray, fine-grained, thin- to thick-bedded, commonly graded graywacke and slate in Marenisco, Mich. area

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.

Mackinac Breccia (Early Devonian) at surface, covers < 0.1 % of this area

Mackinac Breccia

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Biotite schist (Late Archean) at surface, covers < 0.1 % of this area

Quartz-plagioclase-biotite schist of probably intermediate volcanic protolith in area south of Gogebic Range

Baraga Group; Tyler Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Garden Island Formation (Early Devonian) at surface, covers < 0.1 % of this area

Garden Island Formation

Dacite and volcanogenic graywacke (Early Proterozoic) at surface, covers < 0.1 % of this area

Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.

Metagabbro (Early Proterozoic) at surface, covers < 0.1 % of this area

Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi

Sainte Ignace Dolomite (Late Silurian) at surface, covers < 0.1 % of this area

Sainte Ignace Dolomite

Peavy Pond complex (Early Proterozoic) at surface, covers < 0.1 % of this area

Chiefly hornblende metagabbro, but includes metanorite, metatonalite, granodiorite, and granite (Bayley, 1959).

Granitic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Gray to pinkish-gray, mottled, medium-grained syenite, granite, and granodiorite. Moderately strong propylitic alteration and weak cataclasis. Forms small bodies south of Crystal Falls, MI (James and others, 1968). A body near Tobin Location has a U-Pb concordia intercept age of 1840 +/-5 Ma (Z.E. Peterman, written communication, 1988). Includes porphyritic red granite that intrudes Lake Archean Dickinson Group - Red mylonitic gneissic granite (about 1970 Ma).

Rhyolite to dacite (Early Proterozoic) at surface, covers < 0.1 % of this area

Massive to flow-banded rocks of greenschist metamorphic grade in northeastern Wisconsin; virtually undeformed.

Menominee Group; Emperor Volcanic Complex (Early Proterozoic) at surface, covers < 0.1 % of this area

Metamorphosed intermediate to mafic pyroclastic and flow rocks in easternmost part of Gogebic Range

Basaltic and andesitic breccia (Early Proterozoic) at surface, covers < 0.1 % of this area

Exposed in northeastern Wisconsin

Athelstane Quartz Monzonite (Early Proterozoic) at surface, covers < 0.1 % of this area

Pink, coarse-grained granite to granodiorite containing nearly equal amounts of microcline microperthite, plagioclase, and quartz and 5-10 percent biotite and (or) hornblende. Mafic minerals are interstitial and give a clotty appearance.

Portage Lake Volcanics; Rhyolite at Bergland (Middle Proterozoic) at surface, covers < 0.1 % of this area

Portage Lake Volcanics; Rhyolite at Bergland

Prairie du Chien Group (Ordovician) at surface, covers < 0.1 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers < 0.1 % of this area

Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.

Cambrian, undivided (Cambrian) at surface, covers < 0.1 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Schroeder-Lutsen basalts (Mesoproterozoic) at surface, covers < 0.1 % of this area

Unconformably overlies units described below (Mns, Mnu, Mnr, and Mnb).

Sinnipee Group (Ordovician) at surface, covers < 0.1 % of this area

Dolomite with some limestone and shale; includes Galena, Decorah, and Platteville Formations

Gabbroic rocks of Keweenawan affinity (Middle Proterozoic) at surface, covers < 0.1 % of this area

Gabbro, anorthosite, granite, peridotite

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Dacite and volcanogenic graywacke (Early Proterozoic) at surface, covers < 0.1 % of this area

Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.

Rhyolite to dacite (Early Proterozoic) at surface, covers < 0.1 % of this area

Massive to flow-banded rocks of greenschist metamorphic grade in northeastern Wisconsin; virtually undeformed.

Mellen Intrusive Complex; Granite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Mellen Intrusive Complex; Granite (about 1000 Ma)

Basaltic and andesitic breccia (Early Proterozoic) at surface, covers < 0.1 % of this area

Exposed in northeastern Wisconsin

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Coldwater Shale (Mississippian) at surface, covers < 0.1 % of this area

Shale; gray; clayey thin bedded; siderite nodules common; as much as 150 feet thick.

Paleozoic undivided (Paleozoic) at surface, covers < 0.1 % of this area

Paleozoic undivided

Athelstane Quartz Monzonite (Early Proterozoic) at surface, covers < 0.1 % of this area

Pink, coarse-grained granite to granodiorite containing nearly equal amounts of microcline microperthite, plagioclase, and quartz and 5-10 percent biotite and (or) hornblende. Mafic minerals are interstitial and give a clotty appearance. (1836 +/- 15 Ma)

Sunbury and Bedford Formations, Undivided (Devonian and/or Mississippian) at surface, covers < 0.1 % of this area

Shale and siltsone; shale, black to brownish-black, carbonaceous in upper one third of interval, gray to bluish-gray, clayey with occasional siltstone lamina and thin beds in lower two-thirds of interval.

Lower sequence, primarily basalt (Mesoproterozoic) at surface, covers < 0.1 % of this area

Lower sequence, primarily basalt. Includes the Ely's Peak and Grand Portage basalts and Hovland lavas (~1,108 Ma).

Paint River Group; Upper part (Early Proterozoic) at surface, covers < 0.1 % of this area

Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Salina Group (Silurian) at surface, covers < 0.1 % of this area

Dolomite, gray, yellow-gray to olive-gray, laminated to thin bedded; occasional thin bed and laminae of dark gray shale and anhydrite and/or gypsum; brecciated zones in part.

Puritan Quartz Monzonite (Late Archean) at surface, covers < 0.1 % of this area

Pink to pinkish-gray, medium- to coarse-grained, equigranular to inequigranular granite to granodiorite in Puritan batholith south of Gogebic Range. Age 2710 +/- 140 Ma (Sims and others, 1977)

Antrim Shale (Devonian) at surface, covers < 0.1 % of this area

Shale; dark brown to black; carbonaceous, thinly laminated; 0 to 230 feet thick.

Tymochtee and Greenfield Formations, Undivided (Silurian) at surface, covers < 0.1 % of this area

Dolomite, olive-gray to yellowish- brown, thin to massive bedded, upper two-thirds commonly contains brownish-black to gray shale laminae; locally developed brecciated zones in lower one third.

Coldwater Shale (Mississippian) at surface, covers < 0.1 % of this area

Mostly gray shale

Granitic rocks of 1760-Ma age group (Early Proterozoic) at surface, covers < 0.1 % of this area

In northern Wisconsin, granite to granodiorite of varied texture. In southern Wisconsin (not mapped separately), red to pink alkali-feldspar granophyric granite associated with rhyolites of both peraluminous and metaluminous affinities (unit Xr of Marshfield terrane).

Badwater Greenstone (Early Proterozoic) at surface, covers < 0.1 % of this area

Dark-greenish-gray, pillowed to massive tholeiitic basalt and pyroclastic rocks. Correlated with the Hemlock Formation on basis of geology and similarity in chemical composition.

Chocolay Group, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation

Slate and graywacke (Paleoproterozoic) at surface, covers < 0.1 % of this area

Slate and graywacke. Includes the Rove (~1,836 to 1,777 Ma), Virginia (~1,832 Ma near base), and Thompson Formations (youngest zircons in the Thompson Formation ~1,790 Ma).

Metagabbro (Early Proterozoic) at surface, covers < 0.1 % of this area

Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi

Jacobsville Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Portage Lake Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Gabbroic intrusions (Mesoproterozoic) at surface, covers < 0.1 % of this area

Gabbroic intrusions. Including the Sawmill, London, Brule River, Hovland, and Pigeon Point intrusions.

Menominee and Chocolay Groups, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Mapped where units are too thin to show separately on map

Oronto Group; Freda Sandstone; Conglomerate member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Oronto Group; Freda Sandstone; Conglomerate member

Porcupine Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters

Traverse Group (Devonian) at surface, covers < 0.1 % of this area

Dolomite and shale interbedded with limestone; upper part dolomite; gray to light brown; thin to medium bedded; abundant chert; lower part shale interbedded with limestone; olive gray; thin to medium bedded; very fossiliferous; as much as 170 feet thick.

Metabasalt (Late Archean) at surface, covers < 0.1 % of this area

Derived from mafic to intermediate pyroclastic rocks and massive to pillowed lava flows. Unit mapped as Ramsey Formation by Prinz (1981) south of Gogebic Range; mapped as Mona Schist and Kitchi Schist in northern complex of Marquette District.

Puckwunge and Nopeming Sandstones (Mesoproterozoic) at surface, covers < 0.1 % of this area

Puckwunge and Nopeming Sandstones.

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.

Baraga Group; Tyler Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Dundee Limestone (Devonian) at surface, covers < 0.1 % of this area

Limestone; olive gray to brown; upper part thin bedded, lower part medium to thick bedded; fossiliferous in upper part becomes cherty dolomite in lower part; as much as 105 feet thick.

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic) at surface, covers < 0.1 % of this area

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Menominee Group; Ironwood Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Detroit River Group (Devonian) at surface, covers < 0.1 % of this area

Dolomite; brown to gray; medium to thick bedded; laminated; nodules or interbeds of anhydrite and/or gypsum; basal part becomes sandy dolomite or fine-grained sandstone; as much as 170 feet thick.

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers < 0.1 % of this area

Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Paint River Group; Lower part (Early Proterozoic) at surface, covers < 0.1 % of this area

Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group

Menominee Group; unexposed magnetic unit (Early Proterozoic) at surface, covers < 0.1 % of this area

Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).