Gleysols are soils that have undergone prolonged periods of intermittent or continuous saturation with water causing reducing conditions during their genesis. This results in characteristic colours and mottling. Water saturation leads to depletion of oxygen in the soil and cause the transformation of metals such as iron. When oxygen is present, iron is oxidized and has a reddish colour, while when oxygen becomes depleted (due to water saturation) the iron is reduced and takes on a blue-grey hue and this dominates the colour of the horizon. The diagnostic criteria for Gleysolic soils in the presence of well-developed gley features within 50 cm of the soil surface. Horizons with these features are labelled with the subscript g (e.g., Bg, Aeg, Cg).