A forest humus type, transitional between mull and mor, characterized by an accumulation or organic matter on the soil surface in friable Oe horizons, reflecting the dominant zoogenous decomposers. They are similar to mors in that they generally feature an accumulation of partially to well-humified organic materials resting on the mineral soil. They are similar to mulls in that they are zoologically active. Duff mulls usually have four horizons: Oi (L), Oe (F), Oa (H), and A. Oe Horizons have a USDA texture of mucky peat (hemic soil material are Oi horizons. Sometimes differentiated into the following Groups: Mormoder, Leptomoder, Mullmoder, Lignomoder, Hydromoder, and Saprimoder.