What should be marked as 'glossic' when classifying soil layers?

In soil classification, the term 'glossic' specifically refers to certain characteristics of soil horizons located within the argillic horizon. The argillic horizon is a layer within the soil profile that has been modified by the illuviation of clay, which often results in a higher clay content compared to overlying layers. A glossic horizon typically denotes a specific set of features, including shiny or glossy coatings on soil aggregates and a clay content that has been significantly influenced by this illuviation process.

When analyzing the options provided, it is evident that identifying a horizon as glossic is directly associated with its relationship to the argillic horizon. Thus, a layer classified as glossic must either be part of or closely associated with the argillic horizon, which leads to a distinctive soil morphology.

The other options relate to characteristics that do not fulfill the criteria for being considered glossic. Therefore, understanding the definition and classification standards for soil layers is key in identifying and marking appropriate horizons in soil profiles.