Mull humus

Morphologically, two extreme humus forms can be distinguished " (a) mor, which is incompletely decomposed plant material, not incorporated into the lower, inorganic part of the soil, and (b) mull, namely, well decomposed material, thoroughly mixed with the inorganic part of the soil. 

Organic soils, or the deposits from which organic soils are derived, have been designated by many names (Waksman, 1942 Dawson, 1956) but are usually called peats or mucks. Each of these terms has been modified by the use of many special terms based on the plant source of the material, location, land elevation, moisture conditions where formed, pH, amount of salt in the water where formed, mode of origin, inorganic matter content, etc. In addition, there are many synonyms in common use, such as turf, humus, moss and mull. 

---