Which horizon can be classified as mollic?

A mollic horizon is characterized by its dark color, high organic matter content, and good nutrient-holding capacity, typically found in the topsoil of fertile grasslands. It also tends to be thick and has a soft, granular structure. The umbric horizon, which pertains to the correct answer, shares many of these features; it is also dark and organic-rich, but it differs primarily in its base saturation, which is lower than that of a mollic horizon.

In this context, the umbric horizon can be classified as mollic due to its similarities in structure and organic content. The significant attributes that warrant its classification are its rich organic composition and favorable physical properties that improve soil fertility and structure.

Other horizons mentioned, such as the E horizon, are typically characterized by leaching and lower organic matter content, while the albic horizon is a leached layer primarily of sand and silt with little nutrients, and the argillic horizon is characterized by clay accumulation and is usually found below the surface horizons. Therefore, none of these horizons exhibit the defining characteristics of a mollic horizon to the extent that the umbric horizon does.