Named as uppermost formation of Dickinson group (new) for exposures near Six-Mile Lake in sec 22, T42N, R29W, Dickinson Co, northwest MI in Lake Superior region. Rocks are well exposed in low knobs and ridges immediately south of the lake and for several mi to east and west. Unit is a massive, dark, fine- to medium-grained aggregate of hornblende and plagioclase with strong preferred planar and linear orientation of minerals. Amphibolite is basaltic in composition and represents a metamorphosed sequence of flows and possible tuffs. Grades to south into a 1-mi-wide zone of banded gray gneiss that is the product of reaction between amphibolite and post-Dickinson gneissic granite. Overlies Solberg schist. Thickness is about 3,000 ft, but a greater original amount is inferred from widespread occurrence of amphibolite as relict bodies in the gneissic granite that adjoins to south. Stratigraphic sequence chart. Is pre-Animikie in age; assigned to the early Precambrian.

Source: GNU records (USGS DDS-6; Reston GNULEX).