Eluviation

Eluviation is the downward washing-out of fine clay particles, organic matter and soluble minerals from an upper soil horizon as water percolates through it, leaving that horizon visibly paler, coarser-textured and depleted relative to the material it started with. The bleached, ash-grey eluvial horizon typical of podzolized soils in cool, humid, coniferous-forest climates is the clearest visible signature of the process, sitting directly above the darker illuvial horizon where the washed-out material is redeposited. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/