Contains alkali feldspar phenocrysts (0.5-2 cm), subordinate plagioclase and quartz, and rare clusters of biotite with or without hornblende
Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations
Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)
Succession of poorly exposed interlayered metavolcanic and metasedimentary rocks. Lithic units described in Sims (1990)
Ash-flow tuffs and interbedded volcaniclastic sedimentary rocks and cogenetic granite (unit Xga) exposed as inliers in southern Wisconsin. In central Wisconsin pink, flow-banded rhyolite and chert-cemented breccia inferred to be 1760 Ma.
Gray, weakly foliated to massive granite in poorly exposed areas.
Red, coarse-grained rapakivi granite consisting of large (1-3 cm) ovoid alkali feldspar sporadically mantled by plagioclase, interstitial plagioclase, quartz, biotite, hornblende, and ilmenite
Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations
Mylonitic rocks of uncertain lithology in Eau Pleine shear zone
Gray, coarse-grained (1-20 cm) plagioclase-rich (An45-53) rock containing interstitial orthopyroxene, clinopyroxene, Fe-Ti oxides, and apatite.
Rapakivi granite (wiborgite) containing 70-80 percent coarse (1.5 -5 cm) ovoid alkali feldspars mantled by plagioclase, coarse anhedral quartz, and interstitial hornblende and biotite
Gray, medium-grained intrusive rocks, including intrusion breccias. Exposed in central Wisconsin. Zircon ages range from 1837 to 1847 Ma