Is mapped as lowermost formation (of 3) of the North Range Group (Early Proterozoic) in Crow Wing and western Aitkin Cos, central MN (Lake Superior region). Unconformably overlies Mille Lacs Group (Early Proterozoic). Overlain by Trommald Formation of North Range Group. Three informal members separately mapped. Upper member described as gray to light-gray siltstone, argillite, and fine-grained quartzose sandstone containing irregularly distributed beds and lenses of iron-formation and allied anomalously iron-rich sedimentary rocks; base of unit defined arbitrarily as the top of the lowermost mappable iron-formation layer of the middle, iron-formation member. Middle, iron-formation member--interlayered cherty and slaty iron-formation that is similar lithologically to the smaller iron-formation lenses within the upper and lower members; contains rocks formerly assigned to the Trommald Formation and the Emily Member of the Rabbit Lake Formation (Morey, 1978). Lower member--predominantly siltstone, fine- to medium-grained quartzose graywacke, and argillite; also includes minor quartz arenite and irregularly distributed layers and lenses of anomalously iron-rich sedimentary rocks; top of unit arbitrarily placed at lower contact of lowermost mappable iron-formation layer of middle, iron-formation member. Thickness not given.

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