Pg. 78, 81, 86, 97. Amasa formation. One of the iron-bearing formations of the Lake Superior region. Separated by conglomerate from overlying Upper Huronian slates; associated with contemporaneous volcanics, called Hemlock greenstone, at its base. Age is Precambrian. Report includes stratigraphic sequence chart.
[Type area]: occurs on western Menominee Range, in Iron Co., Northern Peninsula, northwestern MI.

Source: US geologic names lexicon (USGS Bull. 1200, p. 74).

Pg. 30 (table 1), 36-37. Amasa formation of Baraga group (new) of Animikie series. Recognized in Iron and Dickinson Counties, northwestern Michigan. Overlies Hemlock formation and underlies Michigamme slate. Occupies same stratigraphic position as Fence River formation (new), but direct equivalence not yet proven. Contains wide variety of rocks: pyritic slate, ferruginous slate and quartzite, chert, and cherty hematitic iron-formation. Aggregate thickness about 1,500 feet. Age is middle Precambrian.

Source: US geologic names lexicon (USGS Bull. 1200, p. 74); supplemental information from GNU records (USGS DDS-6; Reston GNULEX).

Pg. 2845 (fig. 2, stratigraphic chart compiled from Leith and others, 1935; James, 1958; Gair and Thaden, 1968). Amasa Formation of Baraga Group of Marquette Range Supergroup (new; replaces †Animikie series of James, 1958, south of Lake Superior, in Michigan and Wisconsin). Present in Iron River-Crystal Falls district, northwestern Michigan. Overlies Hemlock Formation and underlies Michigamme Slate, both of Baraga Group. Age is middle Precambrian.

Source: Publication.

Amasa Formation of Menominee Group of Marquette Range Supergroup. Includes Fence River Formation of older reports. Variably metamorphosed slaty iron-formation, cherty iron-formation and ferruginous slate. Unconformably (or disconformably) underlies Michigamme Formation of Baraga Group. Overlies and locally interlayered with Hemlock Formation. Amasa and Hemlock transferred to Menominee Group; considered equivalents of iron-bearing sequences of Marquette and Gogebic Ranges. Age is Proterozoic X.
Mapped with Hemlock Formation in Iron River-Crystal Falls area and western Marquette Range, northern Michigan.

Source: Publication.

Amasa Formation of Baraga Group of Marquette Range Supergroup. In the Iron River-Crystal Falls district of Michigan, Baraga Group includes (ascending) Goodrich Quartzite, 150 m; Hemlock Formation, 1,830 m; Amasa Formation, 550 m; Michigamme Formation, 1,830 m; and Badwater Greenstone, 4,570 m. [Cannon (1986) transferred Amasa and Hemlock Formations to the underlying Menominee Group.]

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