with the allocation of the soil to a taxonomic unit. In the following, the diagnostic horizons of two soil classification systems are listed. Diagnostic horizons in the World Reference Base for Soil Resources (WRB) Source: Albic horizon Anthraquic horizon Argic horizon Calcic horizon Cambic horizon Chernic horizon Cohesic horizon Cryic horizon Duric horizon Ferralic horizon Ferric horizon Folic horizon Fragic horizon Gypsic horizon Histic horizon Hortic horizon Hydragric horizon Irragric horizon Limonic horizon Mollic horizon Natric horizon Nitic horizon Panpaic horizon Petrocalcic horizon Petroduric horizon Petrogypsic horizon Petroplinthic horizon Pisoplinthic horizon Plaggic horizon Plinthic horizon Pretic horizon Protovertic horizon Salic horizon Sombric horizon Spodic horizon Terric horizon Thionic horizon Tsitelic horizon Umbric horizon Vertic horizon Diagnostic horizons in the USDA soil taxonomy (ST) Source: Diagnostic surface horizons Anthropic epipedon Folistic epipedon Histic epipedon Melanic epipedon Mollic epipedon (see Mollisols) Ochric epipedon Plaggen epipedon Umbric epidpedon Diagnostic subsurface horizons Agric horizon Albic horizon Anhydric horizon Argillic horizon Calcic horizon Cambic horizon Duripan layer Fragipan layer Glossic horizon Gypsic horizon Kandic horizon Natric horizon Nitic horizon Ortstein layer Oxic horizon Petrocalcic Horizon Petrogypsic horizon Petroplinthic horizon Placic horizon Salic horizon Sombric horizon Spodic horizon See also Archaeological horizon References Citations General sources Soil-Net section on soil horizons. Current version: Soil Survey Manual (March 2017) Pedology