The weathering of rocks, up to hundreds of metres in depth, by air and water, forming saprolite—see Smith et al. (2002) Catena 49, 1–2 on the premisses of deep weathering. Migon and Lidmar-Bergstrom (2001) Earth-Sci. Revs 56, 1 hold that deep weathering has played a major part in the geomorphological evolution of Europe.