gley

A waterlogged soil in which prolonged saturation has driven out oxygen, creating chemically reducing conditions that turn the iron in the soil from rust-red or brown to blue-gray or greenish-gray. A gley soil is soil that has drowned — the color is the evidence. Cut into a gley horizon and the smell is distinctive: a faintly sulfurous, metallic tang of anaerobic chemistry. Patches of orange or rust within the gray indicate intermittent drainage — places where oxygen occasionally reaches the iron and re-oxidizes it.