The defining feature is the gley horizon below the humus-blue-grey clay whowe color is due to ferrous iron compounds that have been reduced by microorganisms, flecked with localized areas of rust-colored oxidized ferric compounds.

• 潜育土的一个重要特点是位于土壤腐殖质层之下，其土层呈灰蓝色是由于含有被微生物还原的亚铁离子，而且常有部分铁被氧化生成红棕色的锈斑。