(Table 6, page 216) Electron microprobe analyses of ferromanganese nodules from Tomahawk Lake, Wisconsin

Oxide coatings on sediments, especially iron, are ubiquitous in the oxygenated environments of most lakes. Deposits of ferromanganese oxides are especially abundant in many lakes in the glaciated regions of North America and Europe. Iron and manganese is readily derived from weathering of mechanically ground, largely crystalline rock debris which is permeable and readily weathered under the humid coldtemperate climate and abundant vegetation. Crusts around pebbles and cobbles constitute much of the most concentrated lacustrine ferromanganese deposits yet reported: Oneida Lake, New York, and Lake Tomahawk, Wisconsin. Freshwater phases tend to be less crystalline than their marine counterparts, possibly a result of faster accretion rates and thus having less time for recrystallization. Electron probe analyses of iron and manganese phases from two nodules from Lake Tomahawk are presented.