Mineral soils conditioned by topography belong to the Reference Soil Groups set #4 of the WRB reference system. This set includes mineral soils whose formation was markedly influenced by their topographic/physiographic setting. In the Lecture Notes on the Major Soils of the World (World Soil Resources Report 94, 2001) 4 Reference Soil Groups are listed. Of those the online version focuses on Fluvisols. For each soil special explanatory notes are compiled in sub-chapters named Excursus, and include characteristic chemical, physical or environmental (landscape, climate…) features of the respective soil:

1. young alluvial FLUVISOLS, which show stratification or other evidence of recent sedimentation
   
   • Excursus: topographic and physiographic characteristics of river systems, deltas and estuaries
     
2. THIONIC FLUVISOLS (or acid sulfate soils)