Peatlands are a subset of wetlands that have accumulated significant amounts of soil organic matter. Soils of peatlands are colloquially known as peat, with mucks referring to peats that are decomposed to the point that the original plant remains are altered beyond recognition (Chapter 6, SSSA 1997). Generally, soils with a surface organic layer > 40 cm thick have been classified as Histosols in the U.S. soil classification system (Soil Survey Staff 1998a). Permafrost-affected soils have recently been classified in the new order, Gelisols, and this includes many soils previously classified as Histosols (Soil Survey Staff 1998a).